Every calculator here names the equation behind it, shows a worked example you can check by hand, and states plainly who the formula describes badly. That last part is the one most calculator sites leave out, and it is usually the most important thing on the page.
Which calculator do you actually need?
Most people arrive looking for one number and need a different one.
If you want to know how much to eat, start with the TDEE calculator — it gives your maintenance calories, which is the figure every other nutrition target is derived from. From there, the calorie deficit calculator turns a goal into a daily target, and the macro calculator splits it into protein, carbohydrate and fat.
If you want to know where you currently stand, the BMI calculator is the fastest screening number but the least informative. A body-fat estimate and a waist-to-hip ratio together tell you considerably more, because they distinguish muscle from fat and capture where that fat is stored.
If you are training, the one-rep max and target heart rate calculators help you set loads and intensities. If you are tracking a cycle, start with the period calculator and use the ovulation calculator for fertile-window estimates.
What every calculator on this site has in common
They all apply a published population-level formula to numbers you type in. That is genuinely all they do. None of them knows your medical history, medications, training background, or body composition, and none is a substitute for a professional who can assess you.
These equations were built to describe averages across large groups, and individuals sit some distance from the average without anything being wrong. Predictive energy equations are typically accurate to within about ten per cent; tape-measure body-fat methods to within a few percentage points. Both are useful for tracking your own trend over months and much less useful as a single verdict.
Treat any number here as a starting estimate to be tested against what actually happens over the following weeks. The scale, the tape measure, and how you feel are the real measurements. The calculator just gets you close enough to start.
Nothing is stored and nothing is sent anywhere — every calculation runs in your browser, and there is no sign-up.