The tracking period decides how much to trust the result

This calculator does not predict your metabolism, it measures it, working backward from what you actually ate and what actually happened to your weight. The days slider is a confidence gauge as much as an input: under a week gets blocked outright, since water and gut contents alone can swing a kilogram day to day and swamp the real signal. Someone who tracks 21 days at 2,000 calories and drops from 80 kg to 78.5 kg lands on a measured TDEE of 2,550 calories, about 5% below what a standard formula would have guessed for the same stats.

Calories and weigh-ins are the two numbers everything rests on

Enter your honest tracked average, not a rounded guess, plus weight at the start and end of the period. The checkbox about weigh-in timing matters more than it looks: a morning weigh-in against an evening one can differ by a kilogram of water and food alone, and answering “no” there quietly lowers how much the result should be trusted, independent of tracking length.

The formula comparison stays optional on purpose

Height, age, sex and activity level never touch your measured number. They only build the second bar in the results, the “standard formula guessed” figure, so the gap between prediction and reality becomes visible instead of abstract. That gap is not an error, it is personal metabolic variance, the same variance research puts at roughly 10 to 30 percent between two people who share a height, weight and age.

When the math flags itself

A measured number below 80% of your estimated resting rate gets flagged directly, since a number that low almost always means under-logged calories rather than a genuinely slow metabolism. The same logic runs in reverse for numbers that come out implausibly high. Rapid weight swings, over 1.5% of bodyweight in a week, get flagged as likely water rather than fat, since the arithmetic on its own cannot tell the difference.

Turning one number into a usable target

The rate slider at the bottom rebuilds a daily calorie target from your measured TDEE instead of the formula guess, so the number you walk away with is built on your own data. The sensitivity range above it answers a different question: how much would this move if your food log itself was off by 100 calories a day, which is a realistic margin for most people’s tracking.