How we build calculators
Every calculator on this site is built by a human, reviewed by a human, and corrected by a human when we find a mistake. Here is exactly how that works, so you can judge for yourself whether to trust the numbers.
Keyword research
Every calculator starts with a real search. We use Ahrefs and Google Search Console data to identify the questions people actually type — "what is 15% of 280", "BMI for 5'7 160 lbs", "mortgage on $420k at 6.5%". The calculator has to answer the question someone is already asking. If the search volume is low, we deprioritise the calculator. If it's high and competing sites answer it poorly, we move it up the queue.
Formula verification
Before a calculator is written, we document the formula in plain text and check it against at least two authoritative sources — government sites (.gov), university publications (.edu), or the original peer-reviewed paper where one exists. For health calculators, the source has to be a body like the NIH or WHO, not a content farm. For finance calculators, the formula has to match what a reputable textbook or regulator publishes.
The formula lives in the calculator's source code as a typed function with unit tests. Every edge case we can think of — zero input, negative input, very large numbers, division by zero — has a test that runs on every deploy. If a test fails, the deploy is blocked.
Content review
Every calculator page has a short human explanation — what the formula does, a worked example with real numbers, and 5–8 answers to common follow-up questions. A human reads the whole page out loud before it ships. If a sentence sounds like marketing or filler, it's cut. We'd rather publish 800 useful words than 1,500 padded ones.
Who writes
All pages are attributed to the OakCalculator editorial team. That team is currently one person — Amir Shehzad, a software engineer based in Ontario — with outside review from a qualified professional when the subject demands it (finance, medical, legal topics). When we use outside review, the page names the reviewer. When we don't, the page doesn't pretend otherwise.
Accuracy policy
Calculators are accurate to the precision of the formula — we round results to six decimals by default, fewer where that's more natural (currency to two, temperature to one). Where a formula has regional variants (US vs metric BMI, for example), the page makes the choice explicit and offers both where it matters.
Calculators are not professional advice. A BMI calculator is not a doctor. A mortgage calculator is not a lender. We say so on the relevant pages. For anything that affects your money, your health, or your legal position, use this as a fast reference and talk to a qualified professional.
Correction process
If you find a mistake, email /contact. We triage within two business days. If the error is real, we fix it, update the page's last-modified date, and add an entry to the changelog describing what changed and why. Meaningful corrections also get a visible note on the calculator page for 30 days.
See it in practice
Our reference calculator page is in progress. When it lands, you'll see every step above applied in one place — research notes, formula, tests, author byline, and changelog. Until then, head back to the homepage to browse the current catalog.