Editorial Policy

How a calculator is built

Each tool implements a named, published formula rather than an approximation invented for the site. The BMI calculator uses the WHO classification; the calorie calculator uses Mifflin-St Jeor; the eGFR calculator uses the 2021 race-free CKD-EPI equation; loan calculations use the standard amortising formula. The formula is named on the page so you can check the working yourself or take it elsewhere.

Where more than one accepted formula exists, the page shows several side by side rather than picking one silently. Ideal body weight, maximum heart rate and body surface area all work this way, because the spread between the accepted methods is itself useful information.

Sourcing

37 calculators carry links to primary sources — the WHO, CDC, NICE, NHLBI, NIDDK, NIAAA, the NHS, ACOG, the American Heart Association, the CFPB, the SEC and peer-reviewed papers indexed on PubMed. Where a calculator states a threshold or a coefficient, the source for that number is linked from the page.

Every source link was fetched before publication to confirm it resolves and points at the document claimed. Candidates that returned a 404, or that redirected to an unrelated page, were dropped rather than published unchecked. Government health and finance sites reorganise their URLs often, so links are re-checked when a page is revised.

Fee and rate data

Marketplace fees change without notice. Every rate used by the selling calculators lives in a single file with a visible “verified as of” date, and every rate is an editable field rather than a number baked into the formula. If a platform changes a fee before we update the page, you can correct it yourself and still get the right answer.

Accuracy and verification

Calculators are checked against known values before release. The margin tools are verified against worked examples — a cost of 10 sold at 15 is a 33.3% margin and a 50% markup; £120 including 20% VAT is £100 net. Health formulas are checked against the worked examples published in their source papers.

This does not make them infallible. It makes errors findable, which is the next best thing.

What these calculators are not

• Not medical advice. Health calculators produce population estimates. They cannot see your medical history, your medication or your individual physiology. Several — eGFR, QTc, anion gap, corrected calcium — implement equations intended to inform a clinician's judgement, not to replace it.
• Not financial or tax advice. Finance and selling calculators model the arithmetic. They do not model your jurisdiction, your tax position, or the specific terms of a product you are being offered.
• Not a substitute for the platform's own figures. Fee calculators estimate. The number on your actual payout statement is the authoritative one.

Corrections

If a calculator returns a wrong result, please tell us. Include the calculator, the exact values you entered, the result you got, the result you expected, and the source for the expected figure if you have one.

Confirmed errors are fixed and deployed as quickly as we can manage, and the calculator's “last checked” date is updated so you can see the page has been revisited. We would rather be told than be wrong quietly.

Independence and advertising

The site is free to use and is funded by display advertising. Advertising has no influence on which calculators exist, what formulas they use, or what the results say. No advertiser reviews content before publication, and there are no paid placements, sponsored calculators or affiliate links inside the tools.

Ads are kept out of the calculator itself and away from its controls, so an advertisement can never be mistaken for part of the tool or clicked by accident. See our privacy policy for how advertising cookies are handled.

Who is responsible

Every calculator is written and maintained by Mohit Patel, named on each page and on the about page. Error reports reach that person directly rather than a support queue.

We do not claim clinical or professional review, and the bylines say “written and maintained by” rather than “reviewed by” for that reason. The health calculators implement equations published in the medical literature and cite them, but no clinician has signed off on the output, and no financial adviser has signed off on the finance tools. Where a page says a formula comes from ACOG, the WHO or a paper indexed on PubMed, that citation is the authority — not us.

If that changes and a qualified reviewer takes on a category, the byline on those pages will say so explicitly and name their credential. Until then we would rather state the limit than imply an expertise the site does not have.

Scope

There are currently 148 calculators across finance, health, selling online, and everyday maths. New tools are added when there is a genuine calculation to perform, not to fill a page. Where two requests resolve to the same formula, they are served by one calculator rather than two near-identical pages.