How these calculators are built
I'm Taylor. I built the 77 calculators on this site. This page explains how they work, so you can decide how much weight to put on a number one of them hands you. It is short on purpose, and there is nothing being sold on it.
Every result here is an estimate
None of these tools measure you. They take the few numbers you type and run them through an equation that was fitted to a group of people, then hand back what that equation predicts for someone with your inputs. You are not the average of that group, so the answer carries error. Depending on the formula, that error can be a rounding difference or it can be several percent.
That is not a disclaimer I am adding to be safe. It is the actual accuracy of the method, and it is why I would rather you treat a result as a starting point you check against reality over a few weeks than as a fact about your body.
Where the formulas come from
Almost all of these are published equations with names: Mifflin St Jeor, Katch McArdle, Epley, Brzycki, the Navy circumference method, and so on. I did not invent them and I do not improve them. Open “Learn the details” on any tool page and you will find the equation written out in words, plus the arithmetic the page just did with your own numbers, so you can check the result by hand if you want to.
75 of the calculators state their method that way. 58 of them also link a published source you can go read yourself, so you are not taking my word for where a threshold came from. Those numbers are checked by a test that reads the real tool code, so this page cannot quietly overclaim as tools change.
The rest have no citation, and I would rather say that plainly than dress one up. A plate loading calculator is arithmetic. A readiness score built from how you rate your own sleep is a structured way of asking you how you feel, not a measurement. When a tool has nothing honest to cite, it cites nothing.
What I do to keep them honest
Input fields have a floor and a ceiling wherever a real range exists, so a slipped decimal point comes back as an error instead of quietly becoming an answer. Where a formula stops being reliable, the tool says so in the same place it shows its method, rather than in fine print nobody opens. And I keep an internal report that reads the source of every calculator and tells me which ones are missing a citation, a stated limitation, or a proper input range. When that report shows a gap, the gap is real and I have not padded the count to make it look better.
What these numbers cannot tell you
They cannot diagnose anything. They cannot tell you whether you are healthy, whether a result is a problem, or what to do about a number you did not like. A body composition estimate from a tape measure is not a body scan. A ratio built from your height and weight cannot tell muscle from fat. A daily calorie target is a prediction of your average, not a rule your body agreed to follow.
If a number here worries you, or you are managing a medical condition, taking medication, pregnant, or under a doctor's care for anything at all, that is a conversation for your doctor and not for a calculator. I am a coach, not a clinician, and nothing on this site is medical advice.
If I have something wrong
Tell me. If a formula is misapplied, a source does not say what I claim it says, or a result is plainly wrong, send it to me through the contact form and I will fix it. I would rather be corrected than be trusted for the wrong reason. There is more about who I am and how this stays free on the about page.