This is a calculator site built on one rule: every number it gives you has a source you can go and read.
What we do
We build calculators for the things people actually need to work out — a loan repayment, a body mass index, a unit conversion, a percentage change. Each one shows its formula, cites where that formula comes from, and explains the places where the obvious arithmetic gives the wrong answer.
That last part is most of the work. A 25% rise followed by a 20% fall lands exactly back where it started. A 50% return over five years is 8.45% a year, not 10%. A month is not four weeks. None of these are hard, and all of them are wrong on calculators that were built to rank rather than to be right.
What we will not do
- Ship a formula we could not read. Several calculators on our list are unbuilt because the authority that publishes the equation does not serve its document to us. We would rather leave a gap than write a constant from memory, because a health or finance formula that is subtly wrong reads exactly like one that is right.
- Present an estimate as a measurement. Where a result has real error in it — a body fat estimate, a calorie burn, an activity multiplier — the page says so and says how much.
- Invent credentials. Author and reviewer names are real people or they are labelled as placeholders. There is no third option.
- Answer a question you did not ask. If a calculation cannot be made from what you entered, we say so rather than quietly assuming a value and returning a plausible number.
How it is paid for
Advertising. Ads never sit inside a result, never move the page while you are reading it, and never load before you have agreed to the cookies that come with them. No calculator’s answer changes because of an advertiser, and no calculator exists because an advertiser asked for it.
Corrections
If a result looks wrong, tell us and include the numbers you entered — that is the fastest route to reproducing it. We would much rather fix a calculator than defend it. Contact us.
More on how pages are written and checked: our editorial policy.