Future Value Calculator

Solve future value, the contribution, the rate or the term, with the deposit frequency independent of the compounding frequency, deposits at the start or end of each period, and the answer in today's dollars.

Solve for Future value Required contribution Required rate Time needed

Starting amount

USD

Contribution

USD

per

End of period Start of period

Annual rate

Compounding

Term — years

Term — months

Inflation

Future value

$264,122

after 20 yr

Total you put in

$130,000

starting amount + 240 deposits

Interest earned

$134,122

Buying power in today's dollars

$146,238

at 3% inflation

Where the ending balance comes from

45% 51%

Starting amount — $10,000
Deposits — $120,000
Interest — $134,122

How the balance grows

Balance
Money you put in

One point per year, at the end of each year.

6.0000% compounded monthly is 6.16778% APY — the effective annual rate.

Deposits: 240 × $500 over 20 yr.

Money is rounded to the dollar, the rate to four decimal places and the term to whole months — once, on the figures above, never inside the calculation.

Year by year

Year	Deposits this year	Interest this year	Balance	In today's dollars
1	$6,000	$785	$16,785	$16,296
2	$6,000	$1,203	$23,988	$22,611
3	$6,000	$1,647	$31,635	$28,950
4	$6,000	$2,119	$39,754	$35,321
5	$6,000	$2,620	$48,374	$41,727
6	$6,000	$3,151	$57,525	$48,176
7	$6,000	$3,716	$67,241	$54,673
8	$6,000	$4,315	$77,556	$61,223
9	$6,000	$4,951	$88,507	$67,833
10	$6,000	$5,627	$100,134	$74,509
11	$6,000	$6,344	$112,477	$81,256
12	$6,000	$7,105	$125,583	$88,081
13	$6,000	$7,913	$139,496	$94,990
14	$6,000	$8,772	$154,268	$101,989
15	$6,000	$9,683	$169,950	$109,085
16	$6,000	$10,650	$186,600	$116,283
17	$6,000	$11,677	$204,277	$123,591
18	$6,000	$12,767	$223,044	$131,015
19	$6,000	$13,925	$242,969	$138,562
20	$6,000	$15,154	$264,122	$146,238

Each row is the balance at the end of that year. Deposits land at the end of each contribution period and interest compounds monthly.

What each compounding frequency is worth

Compounding	APY	Ending balance
Annually	6.00000%	$258,791
Semiannually	6.09000%	$261,635
Quarterly	6.13636%	$263,114
Monthly	6.16778%	$264,122
Biweekly	6.17632%	$264,397
Weekly	6.17998%	$264,515
Daily	6.18313%	$264,616
Continuously	6.18365%	$264,633

Same starting amount, contribution, rate and term as above. APY is the effective annual rate, (1 + r/m)^m − 1, as 12 CFR 1030 Appendix A defines it.

How long it takes to double at this rate

Rule of 72: 72 / 6 = 12.00 years

Exact: ln 2 / ln(1 + 0.06) = 11.90 years

The rule of 72 is 0.10 years too slow at this rate. It is exact near 7.85 %.

With deposits the balance doubles sooner than either figure: the rule covers a lump sum only.

Both figures are for a lump sum compounding once a year: no deposits, and not the compounding frequency picked above.

The same answer in a spreadsheet

Excel or Google Sheets: =FV(0.005, 240, -500, -10000, 0)

Rate per contribution period: i = (1 + 0.06/12)^(12/12) − 1 = 0.005

Money you pay in is negative, which is why the starting amount and the contribution carry a minus sign.

The last argument is 0 for deposits at the end of a period and 1 for the start.

Spreadsheet functions take the rate per period, which is the conversion above — the step most people get wrong.

Prefer the retail framing — initial balance, monthly deposit, final balance? Open the compound interest calculator.

This calculator is for informational purposes only. It does not constitute financial advice.

Updated: August 20, 2026

Future value calculator. Ending balance, or the deposit, rate or time needed to hit a target.

A future value calculator projects what a balance grows to: $10,000 plus $500 a month at 6% compounded monthly reaches $264,122 in 20 years. It also runs the other way — the deposit, rate or number of years needed to reach a target — and converts the result into today's dollars at the inflation rate you choose.

What Is Future Value?

Future value is what a sum of money is worth at a later date once interest has been added to it. Put $10,000 into an account paying 6% a year compounded monthly, add $500 at the end of every month, and after 20 years the balance is $264,122. Of that, $130,000 is money you handed over — the starting amount plus 240 deposits — and $134,122 is interest. The page splits the ending balance into those three shares: interest 51%, deposits 45%, and the starting amount the sliver under 4% that is left.

The relation behind that number ties five quantities together — the starting amount, the deposit, the rate, the term and the ending balance — and knowing any four fixes the fifth. This page solves in all four useful directions from one selector. Required contribution turns a $500,000 target into $1,011 a month over the same 20 years at 6%. Required rate, on the same target with $500 a month, returns 10.6969% nominal compounded monthly. Time needed, aimed at $1,000,000 at 7%, returns 34 yr 10 mo and prints the balance at that month, $1,002,852, beside it. Banks tend to split those questions across separate URLs — M&T Bank publishes the required-rate one on a page of its own, Bankrate the required-deposit one on another — and here they are one form, so changing the question costs a click rather than a fresh search.

Two frequencies live inside the arithmetic, and a form that offers only one of them has decided the other on your behalf without telling you. How often you deposit and how often the account credits interest are separate facts about an account, and this page keeps them apart. Deposit monthly into something that compounds once a year and the same 6% over the same 20 years lands at $258,791 instead of $264,122 — a bit over $5,300 of difference — because a deposit made in March waits until December before any of it starts compounding. The SEC's own compound interest calculator on investor.gov shows how ordinary the mismatch is: it fixes the contribution at monthly while offering compounding from annually through to daily, so the case arises there with no control over it.

When the two differ, the page says so under the results: deposits are 12×/year, interest compounds 1×/year, and each deposit earns the rate for the part of a compounding period it is actually in the account. Pick continuous compounding and the wording changes to match, because then each deposit earns the rate for the exact time it is in the account.

Whether deposits land at the start or at the end of a period is the other assumption that usually goes unstated. A deposit made at the start of each period collects one extra period of interest, so the whole balance comes out higher by one period's worth: the beginning-of-period balance is the end-of-period balance multiplied by one plus the periodic rate. CalculatorSoup prints that switch inside its published formula as a (1 + iT) factor. Excel calls it the TYPE argument, and Microsoft's documentation states that if type is omitted it is assumed to be 0 — the end of the period. This page defaults to the end for the same reason, and puts the control on the form rather than in a footnote.

The fourth card turns a disclaimer into a number. At 3% inflation the $264,122 balance buys what $146,238 buys today, about 55 cents on the dollar, and it sits next to the nominal figure instead of under it as a caveat. GIGAcalculator states the problem without solving it, warning on its own page that the future value it computes is nominal and does not take inflation into account. The 3% in the field is a round starting assumption and nothing more: no historical average is claimed for it, and the number that belongs there is your own.

If your deposits and your compounding are both monthly and the forward answer is all you want, the compound interest calculator asks the same question in a saver's vocabulary — starting balance, monthly deposit, final balance. This page is the one to open when the two frequencies differ, when the timing matters, when you know the target and not the input, or when you want the answer in today's money.

How to Use the Future Value Calculator

Ten controls sit on the form at any one time and all of them are visible at once. Two of them set how often you deposit and how often interest compounds, and keeping those two apart is the reason this page exists.

1. Solve for. Four modes: Future value, Required contribution, Required rate and Time needed. Whichever quantity becomes the answer leaves the form, so you are never asked for the number you came to find, and a Target balance field appears in the three reverse modes.

2. Starting amount. What is in the account on day one. Set it to 0 if you are starting from nothing — the deposits alone still work, and the split bar drops its first slice.

3. Contribution, per, and Contributions at. Three fields on one row because they are one decision: how much, how often — month, two weeks, week, quarter, half-year, year, or none — and whether each deposit lands at the start or the end of its period. The page loads with $500 a month at the end.

4. Annual rate and Compounding. The rate is nominal, which is the rate a formula wants, and the effective annual rate appears with the results: at the default it reads 6.0000% compounded monthly is 6.16778% APY. Compounding runs from annually through daily to continuously and moves independently of the row above it.

5. Term and Inflation. Years and months are separate fields, so 10 yr 6 mo needs no decimal. Inflation feeds the today's-dollars card only; it never touches the nominal balance.

Five cards read out the answer and they keep their places between modes. The lead card is Future value, or Contribution needed, Rate needed, Time needed. Total you put in adds the starting amount to the deposits and names the count — on the default state, starting amount plus 240 deposits, $130,000. Interest earned is the balance minus that, $134,122, and it turns red when a negative rate makes it negative. Buying power in today's dollars, $146,238 at 3%, is the fourth. The fifth is the split bar showing where the ending balance came from.

Below the cards, four blocks answer the questions the cards raise. The growth curve plots the balance against the money you put in. The year-by-year ledger gives deposits, interest, balance and balance in today's dollars for every year, with year 1 reading $6,000 of deposits, $785 of interest and a $16,785 balance, and year 20 reading $6,000, $15,154 and $264,122. A frequency table prices all eight compounding options at once, a doubling block sets the rule of 72 against the exact figure, and a spreadsheet block prints the call that reproduces whatever is on screen, so the answer is checkable in Excel or Sheets in one paste.

Anything you change is written into the address bar, which makes the URL the whole scenario: bookmark it, or send it to whoever asked you the question.

The Formula, and the Rate That Goes Into It

FV = PV\left(1 + \frac{r}{m}\right)^{mt} + PMT \cdot A

$FV$ = Ending balance — what the account holds when the term is up
$PV$ = Starting amount, the balance on day one
$PMT$ = Contribution paid in once per contribution period
$r$ = Nominal annual rate as a decimal: 6% is 0.06. This is the advertised rate, not the APY
$m$ = Compounding periods per year: 1 annually, 12 monthly, 365 daily, unbounded for continuous
$p$ = Contribution periods per year: 12 for monthly deposits, 26 for every two weeks. Independent of m, and that independence is the point
$t$ = Term in years — whole years plus months divided by 12
$T$ = Timing switch: 0 when deposits land at the end of a period, 1 when they land at the start
$A$ = Annuity factor — what a single unit of contribution accumulates to over the whole term

The formula for future value is the starting amount grown for the whole term, plus everything the deposits accumulate to:

FV = PV\left(1 + \frac{r}{m}\right)^{mt} + PMT \cdot A

The first term is the plain compound-interest formula. The second is where the two frequencies meet, and it needs a rate per contribution period rather than a rate per compounding period:

i = \left(1 + \frac{r}{m}\right)^{m/p} - 1

That conversion is what the spreadsheet block below the calculator calls the step most people get wrong. When deposits and compounding are both monthly, the exponent is 1 and i collapses to the annual rate over twelve — 0.005 at 6% — which is why the shortcut works often enough to look like a rule. When the two differ it does not collapse: monthly deposits into an account that compounds once a year make the exponent one twelfth, and i becomes the twelfth root of 1.06 minus one. That figure is smaller than 0.005, which is why the shortcut runs high rather than low. Under continuous compounding the same conversion is i = e^(r/p) − 1 and the lump-sum factor becomes e^(rt).

With N contribution periods, where N is p times t, and N a whole number, the accumulation is the textbook annuity form:

FV = PV\left(1 + \frac{r}{m}\right)^{mt} + PMT \cdot \frac{(1 + i)^{N} - 1}{i} \cdot (1 + iT)

The factor on the end is the timing switch: T is 0 for deposits at the end of a period and 1 for the start, worth exactly one extra period of interest on every deposit. CalculatorSoup prints the same factor in its published formula, which is one of the reasons its worked example reproduces here to the cent. When i is zero that middle fraction is undefined and the accumulation reduces to the deposit count, which is why a 0% projection returns your deposits and no error message.

The effective annual rate under the rate field is the other half of the same idea:

APY = \left(1 + \frac{r}{m}\right)^{m} - 1

That is the formula Regulation DD sets — 12 CFR Part 1030, Appendix A — for what a US bank must advertise, and the regulation works its own example: an institution paying $61.68 of interest for a 365-day year on $1,000 has an annual percentage yield of 6.17%. 6% compounded monthly pays exactly that, and the page prints it to five places as 6.16778%. The regulation's wording is worth keeping in mind, because it explains why the number moves at all: the annual percentage yield measures the total amount of interest paid on an account based on the interest rate and the frequency of compounding.

Both facts turn up in the spreadsheet block, which prints the call for the state on screen. For the default that is =FV(0.005, 240, -500, -10000, 0), and the 0.005 is the conversion above rather than a number typed by hand. Microsoft gives the syntax as FV(rate, nper, pmt, [pv], [type]), notes that cash you pay out, such as deposits to savings, is represented by negative numbers, and states that if type is omitted it is assumed to be 0. Microsoft's own worked example tells you to use 12%/12 as the rate for monthly payments — correct when the rate is nominal compounded monthly, and the habit to drop the moment your account credits interest once a year.

Worked Future Value Examples

The state the page opens on: $10,000 and $500 a month at 6%

Leave every field as it loads. Starting amount $10,000, contribution $500 per month at the end of each period, 6% nominal compounded monthly, a 20-year term, 3% inflation. Future value is $264,122 after 20 yr. Total you put in is $130,000 — the starting amount plus 240 deposits — and interest earned is $134,122, so by the end the interest has overtaken everything you paid in. Buying power in today's dollars is $146,238 at 3% inflation.

The ledger shows the shape of it. Year 1 adds $6,000 of deposits and $785 of interest for a $16,785 balance. Year 20 adds the same $6,000 of deposits and $15,154 of interest, more than nineteen times the first year's interest on an identical deposit. The deposit never changes; what changes is the balance it is landing on.

Monthly deposits into an account that compounds once a year

Change one control: set Compounding to Annually and leave everything else alone. Future value drops from $264,122 to $258,791. The APY line goes from 6.16778% to 6.00000%, because with annual compounding the nominal rate and the effective rate are the same number. The deposits have not moved — still 240 of them, still $130,000 in — and interest earned falls from $134,122 to $128,791.

A line then appears that names which frequency is doing what: deposits are 12×/year, interest compounds 1×/year, and each deposit earns the rate for the part of a compounding period it is actually in the account. That single sentence is the difference in words. A March deposit sits in the account until the December credit before it compounds at all, and that lag, repeated across every deposit for twenty years, is worth a bit over five thousand dollars.

How much a month reaches $500,000 in 20 years

Set Solve for to Required contribution and the Target balance field appears. Leave it at $500,000. With $10,000 already in the account, 6% compounded monthly and a 20-year term, the answer is $1,011 per month. Total you put in becomes $252,523 — the same 240 deposits, each of them larger — and interest earned is $247,477, so almost exactly half the target is interest rather than savings.

The fourth card is the one to act on. That $500,000 is $276,838 at 3% inflation, so a half-million twenty years out does the work of a bit over a quarter-million today. If the target was chosen because half a million sounds like enough, this is where you find out whether it still is.

What return the same target would demand

Keep the $500,000 target and the $500 a month, and switch to Required rate. The answer is 10.6969%, nominal, compounded monthly, printed to four decimal places because a reader round-trips it. Total you put in stays $130,000 and interest earned is $370,000 — the target is asking the market for nearly three dollars of growth for every dollar you deposit.

The rate is what the target demands; whether anything pays it is a separate question. A required rate near 10.7% is a demanding assumption to carry for two decades, so the useful response is usually to lengthen the term or raise the deposit until the figure lands somewhere you would be willing to defend. The page returns negative rates too, when the target sits below what the deposits alone come to.

How long $500 a month takes to reach $1,000,000

Switch to Time needed, set the target to $1,000,000, the rate to 7%, and keep $10,000 and $500 a month. The answer is 34 yr 10 mo, with the balance at that point, $1,002,852, printed under it. Total you put in over those years is $219,000 across 418 deposits, and interest earned is $783,852 — more than three and a half times what you paid in.

The term answer is deliberately a whole month rather than a decimal year. Under start-of-period timing the balance jumps by a full deposit at every deposit, so a fractional-year root can name an instant the balance never actually holds. What the page reports is the first whole month at which the target is met, which is a date you can put in a calendar.

A negative rate, and what the cards do with it

Type -3 into the annual rate and the page computes it instead of refusing: future value $95,804 after 20 yr, total you put in $130,000, and interest earned -$34,196 in the red tone the card switches to when growth turns negative. Buying power in today's dollars is $53,044, a negative return and 3% inflation working against each other on the same balance.

The APY line reads -3.0000% compounded monthly is -2.95909% APY. The split bar closes the interest slice to nothing and shows deposits at 92% of what is left. The doubling block disappears, since nothing doubles at a negative rate. This is also the clearest read of the buying-power card: a negative return and inflation are the same kind of arithmetic pointed the same way, and here you can watch them stack.

What Each Compounding Frequency Is Worth

Compounding	APY	Ending balance
Annually	6.00000%	$258,791
Semiannually	6.09000%	$261,635
Quarterly	6.13636%	$263,114
Monthly	6.16778%	$264,122
Biweekly	6.17632%	$264,397
Weekly	6.17998%	$264,515
Daily	6.18313%	$264,616
Continuously	6.18365%	$264,633

Where Future Value Calculations Go Wrong

Dividing the annual rate by 12 when the account does not compound monthly. The rate a deposit formula wants is the rate per deposit period, and that equals the annual rate over twelve only when interest also compounds monthly. With monthly deposits into an account that credits interest once a year, the correct conversion gives a smaller periodic rate than the division does, so the shortcut runs the balance high. The page prints the conversion it used beside the spreadsheet call, so you can see which one you are getting.
Entering the APY where the nominal rate goes. 6% compounded monthly is 6.16778% APY, and the two figures describe the same account. Put the APY in the rate field with compounding still on monthly and the page compounds an already-compounded number, so the projection drifts upward for no reason an account would recognize. The nominal rate is the input; the APY is printed with the results as the output.
Leaving the deposit timing to a guess. A deposit at the start of each period earns one extra period of interest, on every deposit, so the two settings only agree when the rate is zero. Omnicalculator's future-value page surfaces no timing control, which means the assumption is made for you and never stated. Decide which one matches the account in front of you: a payroll deferral comes out of a period's pay, so it lands at that period's end, while a standing order on the 1st lands at the start.
Reading a nominal balance as spending power. $264,122 in twenty years is not a figure you can hold up against today's prices. At 3% it buys what $146,238 buys now. Any projection longer than a few years needs that second number before a decision can rest on it, and the inflation rate that produces it is a guess you own rather than a fact the page supplies.
Changing the deposit frequency without changing the deposit. Switch per from month to two weeks and $500 a deposit stops meaning $6,000 a year and starts meaning $13,000, because 26 deposits replace 12. Over a 20-year term that is 520 deposits rather than 240, so the balance rises mostly because you paid more in. The deposits line under the cards prints the count and the amount for exactly this reason.
Expecting the rounded ledger to add up. Money is rounded to the dollar, the rate to four decimal places and the term to whole months, and the rounding happens once, on the figures shown, never inside the calculation. A column of rounded yearly interest therefore need not total the rounded interest figure on the card. The page states the policy on screen rather than leaving you to find it in a spreadsheet.
Treating a required rate or a required deposit as a plan. 10.6969% is what a $500,000 target demands from $500 a month over 20 years; whether anything pays it is a separate question. The same applies in the other direction: if the required deposit comes out at $1,011 a month and your budget is $600, the lever is the term or the target. The reverse modes exist so you find that out before committing to anything.
Forgetting the sign convention in a spreadsheet. Excel and Sheets treat money you pay in as negative, which is why the printed call carries minus signs on both the starting amount and the deposit: =FV(0.005, 240, -500, -10000, 0). Enter them as positives and the answer comes back negative, which reads like a bug and is the convention doing its job.

What This Page Does Not Model

One deliberate boundary runs through the calculation. Contributions and the starting amount are floored at zero, so the page models accumulation and not decumulation. That is a mathematical constraint rather than a missing feature: the required-rate answer is found by bisection, which needs the balance to rise as the rate rises, and a negative contribution introduces a second root that would let the search return either one. A withdrawal plan is a different calculation with a different failure mode and it belongs on its own page.

Taxes, fees and expense ratios are absent, and so are variable rates, an uneven series of cash flows, and a contribution that grows with your salary. Each of those is a genuine feature of a genuine account, and each one adds an assumption the answer then rests on. If your question is a stream of irregular cash flows rather than a level deposit, net present value and internal rate of return are the tools for it.

The rate is a single fixed number for the whole term. Markets do not deliver a long-run average as a sequence of average years, so 6% here is a statement about an average and not a forecast of any particular year. Run the calculation twice, once pessimistic and once optimistic, and treat the pair as the answer rather than either figure on its own.

The inflation default is 3% and it is an assumption, not a measurement. No historical average is claimed for it and none is cited, because the field is there for your own number.

One internal detail is worth stating plainly. When the term is not a whole number of contribution periods — quarterly deposits over 10 years and 1 month, for instance — the last part-period earns interest and takes no deposit, and a line under the cards says so. That model is continuous in the term, matches the textbook closed form whenever the number of deposit periods is a whole number, and never silently truncates a partial period. What it has no external benchmark against is any competitor, because none of them documents what it does there.

Future Value Calculator — Frequently Asked Questions

How do I calculate future value?

Grow the starting amount for the whole term, then add what the deposits accumulate to. $10,000 at 6% compounded monthly plus $500 a month for 20 years reaches $264,122 — $130,000 paid in and $134,122 of interest.

What is $500 a month worth after 20 years?

With $10,000 already in the account and 6% a year compounded monthly, $500 at the end of every month reaches $264,122 after 20 years. The deposits are $120,000 of that and interest is $134,122. Starting from zero instead changes the balance, and the calculator shows it the moment you clear the field.

How do I calculate future value when deposits are monthly but interest compounds annually?

Convert the rate to a rate per deposit period first: one plus the nominal rate over the compounding count, raised to the compounding count divided by the deposit count, minus one. With monthly deposits and annual compounding at 6% that is the twelfth root of 1.06 minus one, rather than 6% split twelve ways. Set Compounding to Annually and per to month and the page does the conversion for you: $10,000 plus $500 a month at 6% over 20 years comes to $258,791 with annual compounding against $264,122 with monthly.

How much do I need to save each month to reach $500,000?

Set Solve for to Required contribution and enter the target. From $10,000 at 6% compounded monthly over 20 years the answer is $1,011 a month, which puts $252,523 in and earns $247,477. Shorten the term and the required deposit climbs steeply, because interest has less time to carry any of the load.

What rate of return do I need to hit my target?

Switch to Required rate. A $500,000 target from $10,000 plus $500 a month over 20 years needs 10.6969% nominal, compounded monthly. Four decimal places are shown because a reader tends to put the number straight back in to check it, and negative rates are returned rather than blocked when the target falls below what the deposits alone come to.

How long will it take to reach $1 million?

At 7% compounded monthly, $10,000 plus $500 a month reaches $1,000,000 in 34 yr 10 mo — 418 deposits, $219,000 paid in and $783,852 of interest. The page reports the first whole month the target is met, with the balance at that month.

Does compounding frequency actually matter?

Less than the rate and the term. On the same $10,000, $500 a month, 6% and 20 years, annual compounding gives $258,791 and continuous gives $264,633, with every option in between inside that band. The APY column is the cleaner comparison: 6.00000% against 6.18365%.

Should contributions be at the beginning or the end of the period?

Match your account. A deposit at the start of each period earns one extra period of interest, so the beginning-of-period balance is the end-of-period balance times one plus the periodic rate. Excel defaults to the end and so does this page; a deduction from a period's pay lands at that period's end.

Is APY the same as the interest rate I should enter?

No. Enter the nominal rate, which is the advertised annual rate before compounding, and read the APY the page prints back: 6% compounded monthly shows 6.16778%. Regulation DD, at 12 CFR Part 1030 Appendix A, defines the annual percentage yield as the total interest an account pays given the rate and the frequency of compounding, and works the example itself — $61.68 of interest over a 365-day year on $1,000 is a 6.17% APY.

How do I reproduce this in Excel or Google Sheets?

The page prints the call. For the state it loads with, that is =FV(0.005, 240, -500, -10000, 0): the rate per deposit period, the number of deposits, the deposit, the starting amount, and 0 for deposits at the end of a period. Two things usually go wrong — the rate, which is per deposit period and not per year, and the signs, since money you pay in is negative. Both are written out under the calculator, and RATE, NPER and PMT get the same treatment in the other three modes.

Is future value the same thing as compound interest?

They are two views of one calculation. Compound interest is the mechanism, where interest credited to the balance makes the next credit larger, and future value is the result that mechanism produces by a given date. A future-value page adds the deposit schedule, the timing and the reverse directions on top of it. If your deposits and your compounding are both monthly and the forward answer is all you need, the compound interest calculator is the shorter route to the same number.

How accurate is the Rule of 72?

Close enough for mental arithmetic across the range people use it in. At 6% the rule gives 72 divided by 6, or 12.00 years, while the exact figure — ln 2 over ln 1.06 — is 11.90, so the rule runs 0.10 years slow. It is exact near 7.85% and drifts either side of that. Both numbers describe a lump sum compounding once a year: with deposits the balance doubles sooner than either, because the rule takes no account of new money arriving.

Can it model withdrawals, or a contribution that grows each year?

Neither. The deposit and the starting amount are floored at zero, which keeps the balance rising with the rate and lets the required-rate search return a single answer; a negative deposit would give it two. A growing contribution is out for a different reason — it adds an assumption for a case that a second run at a higher deposit approximates well enough. Taxes, fees and an uneven series of cash flows are outside the form as well.

Why is the today's-dollars figure so much lower than the future value?

Because inflation compounds too. Over 20 years, 3% a year takes $264,122 down to $146,238 of present spending power, about 55 cents on the dollar. Lower the inflation field and the gap narrows; set it to 0 and the two cards agree. It is one division, and it is the one that decides whether a target is actually enough.

Can I use this for a 401(k), an IRA or a taxable brokerage account?

For the growth arithmetic, yes — the mechanics are the same whatever the wrapper, and the deposit frequency control is useful here because payroll contributions arrive every two weeks rather than monthly. What the page does not carry is tax treatment, which is where those accounts differ most: a traditional 401(k) or IRA defers tax until money comes out, a Roth taxes the contribution instead, and a taxable account can owe something along the way. Model the deposits and the rate here, then apply your own account's tax rules to the ending balance.

Is this future value calculator free, and where do my numbers go?

It is free, nothing is stored and nothing leaves the page — the whole calculation runs in the browser you are reading this in. All four solve directions, the year-by-year ledger, the frequency table and the spreadsheet block sit on this one page, and anything you change is written into the address bar, so a link reopens the same scenario exactly as you left it.

I have the number — what should I do with it?

Read the interest share before the headline figure. On the state the page loads with, interest is 51% of the balance against 45% from deposits: when that share is small, the term is short or the rate is optimistic, and over a long horizon the term is usually where the biggest change comes from. Then read the today's-dollars card, because that is the number your future self spends. Then run the reverse direction — put your real target in and see what deposit or what term it demands, which is a more useful answer than any single forward projection.

Sources & References

Content verified by the Smart Calculators Team