How We Ensure Accuracy

Formulas Come From Named, Checkable Sources

Before a single line of a calculator is written, we track down where its formula actually comes from — a peer-reviewed paper, an official standard, or a well-documented industry convention — and write it down in plain terms. For example, our FFMI calculator uses the normalized formula from Kouri et al.'s 1995 bodybuilding research, and our Cooper test calculator uses the exact distance-to-VO2max formula Kenneth Cooper published in 1968. Where a topic has real health, financial, or safety consequences and we couldn't find a source we were confident in, we don't publish a calculator at all rather than guess.

Every Formula Is Checked by Hand First

Before any calculator goes live, we run its formula manually against at least one known or plausible example — often a worked example from the original source itself — and confirm the numbers line up. Only once that hand-checked result matches do we build the actual page around it.

Every Calculator Is Tested, Not Just Written

Once a calculator is built, we test it directly in a browser: valid inputs have to produce the same result we calculated by hand, invalid or missing inputs have to trigger a clear error message instead of a broken or misleading result, and the page has to run with zero script errors from start to finish. We also check the finished page visually to make sure nothing overlaps, truncates, or looks out of place on different screen sizes.

What These Calculators Are — and Aren't

These tools are built to be accurate given the inputs you provide, but they're estimates based on general formulas, not personalized advice. A calorie, macro, or FFMI estimate doesn't know your medical history; a debt payoff or FIRE projection doesn't know what the market will actually do; a due date estimate doesn't replace an ultrasound from your own doctor. Use these calculators to build intuition and compare scenarios quickly, and check anything with real financial, medical, or legal stakes against a qualified professional before acting on it.

Something Looks Wrong?

If you spot a result that doesn't match the source formula, or a calculator that behaves unexpectedly, we want to know. Mistakes are possible despite the process above, and we'd rather fix them than leave them live.