Vores metode
Hvor vores formler kommer fra, hvordan vi verificerer resultaterne, og hvordan vi holder siderne opdaterede.
How We Calculate
Every result on Smart Calculators comes out of a formula someone can check. This page explains where those formulas come from, how we test them before and after publishing, and what the "Updated" date at the top of each calculator actually means.
We publish more than 80 calculators in over 40 languages. That scale only works honestly if the verification is systematic rather than ad hoc — so we made it systematic, and we document it here.
Where the formulas come from
We never invent a formula. Each calculator starts from the most authoritative source available for its domain, and that source is cited at the bottom of the calculator's page under "Sources".
For financial tools that means official bodies: consumer-protection regulators, tax agencies, and public documentation from institutions such as the CFPB or Freddie Mac for loan and mortgage amortization. For health tools we use peer-reviewed equations — the BMR calculator implements Mifflin-St Jeor, not a simplification of it. Converters follow published standards: ring sizes trace to ISO 8653, units to their SI definitions. Calendar tools state which variant they implement (for example, the tabular Islamic calendar) because "the" conversion often has more than one legitimate convention. Gaming calculators are grounded in the games' own published data and mechanics, cross-checked against community-verified wikis.
When a domain has competing conventions, we pick one, say which, and explain it on the page rather than averaging them silently. A concrete example: for people born on February 29, our age calculator observes the birthday on March 1 in non-leap years — a documented choice, stated on the page, not a hidden quirk.
How results are verified
Each calculator is a deterministic calculation engine, separate from the interface, and every engine is covered by an automated test suite — more than 25,000 checks run against the site before any change ships. The tests pin worked examples from the cited sources, boundary cases (leap years, zero and negative inputs, rounding at currency precision), and cross-reference results against independent implementations of the same math.
On top of the automated suite, every published example you read in the explanatory text below a calculator is recomputed against the engine itself before publication. If the text says a scenario yields a specific number, that number came out of the same code you are using on the page — not from a copywriter's estimate.
What the "Updated" date means
The date shown at the top of a calculator's explanation is the real date of its last editorial review — not a decorative timestamp. We update it when the content or the calculation it describes actually changed, and we leave it alone otherwise.
Calculators tied to regulation or tax years (salary, VAT, severance) are re-checked when the underlying rules change. Timeless math (percentages, unit conversions) changes rarely, and its dates reflect that honestly.
What our calculators are not
These tools produce educational estimates. They are not financial, medical, or legal advice, and results should not replace a professional who can see your full situation. Tax and salary calculators simplify edge cases that a professional adviser would catch; health indicators like BMI have documented limitations that we list on their own pages.
We would rather tell you a calculator's limits on the page than let a clean-looking number imply more precision than it has.
Found an error?
If a result looks wrong, we want to know. Reach us through the contact page and include the inputs you used. Confirmed errors get fixed in the engine, covered with a new automated test so they cannot silently return, and the page's review date is updated — the same process our own internal audits follow when they catch something.
Frequently Asked Questions
As accurate as the cited formula allows. Engines are tested against worked examples from the official sources listed on each calculator's page, with more than 25,000 automated checks across the site. Where a formula has known error margins — like body-fat estimation methods — we state them instead of hiding them.
A small independent team. Every calculator page carries a verification byline and a real review date, each cites its sources, and corrections are handled through the contact page. We don't publish anonymous, unsourced tools.
When the thing they model changes. Regulation-dependent calculators are re-checked when rules change; standards-based converters change only if the standard does. The "Updated" date on each page reflects its own last review, not a site-wide refresh.
Use it to understand and to sanity-check, not as a substitute for the official figure. For anything binding — taxes, severance, medical decisions — confirm with the official calculator or a professional. Our pages link to the authoritative sources so you can do exactly that.