How this TDEE calculator works
TDEE is total daily energy expenditure — everything your body burns in a day, from resting metabolism to workouts to fidgeting. This calculator estimates it with the Mifflin-St Jeor equation, which predicts resting metabolism from your age, sex, height, and weight; if you enter a body-fat percentage, it switches to Katch-McArdle, which works from lean mass instead. Everything above resting is then added up from things you can look up rather than guessed at with a single "how active are you?" multiplier: your typical step count, the part of your job a step count can't see, and your training — with anything your tracker already counted netted out, so the same movement is never billed twice. The answer is a range. The tool is free, there are no ads, and there's no email gate — every calculation runs in your browser tab, and nothing you type leaves it.
Why we show a range instead of one number
Most calculators hand you a single confident number like 2,347. The research doesn't support that confidence. A 2005 systematic review by Frankenfield and colleagues found that Mifflin-St Jeor — the best of the common equations — predicts measured resting metabolism within 10% for roughly 82% of people. That's the best case. For the rest, the miss is larger, and for a substantial share of users a formula is off by 250 calories a day or more. Off by 250 means a planned 500-calorie deficit could really be 250, or 750 — the difference between slow progress and none, or between sustainable and miserable. So instead of borrowing a precision the math doesn't have, we show the band where your maintenance most likely sits and tell you how wide it is.
Adaptive TDEE: the more accurate method nobody uses
There's a better method than any formula, and it needs no lab: watch what your weight actually does at a known intake. Log two to four weeks of daily weigh-ins alongside your calories over the same stretch, and arithmetic on the trend backs out your real maintenance — the number your body voted for, not the one a population equation guessed. That's what the measurement section above does. It absorbs the daily water-weight noise, measures the underlying rate of change, and converts it to calories. A formula can't see your genetics, your hormones, how much you move outside the gym, or how honestly you log; a measured trend prices all of that in automatically. Almost nobody uses this method, because it asks for a few weeks of patience. It's worth it.
What to do with your number
Treat the range as a starting hypothesis, not a verdict. Pick an intake modestly below the band to lose, modestly above it to gain, hold it for a few weeks, and let your weight trend tell you whether the hypothesis was right. Once you have a target, the goal timeline tool takes your deficit and shows when you'd arrive. The weight trend calculator helps you read the weigh-ins themselves, and if the daily bounce is stressing you, start with why daily weight changes when the plan is working. If your scale already writes to Apple Health, tracking weight trends with Apple Health shows how to make the whole loop automatic.
Coming off a deficit, and recomposition
The end of a diet is the part nobody plans. The clearest evidence for how that goes comes from the STEP 1 trial extension: 327 people who had lost 17.3% of their body weight on semaglutide were followed for a year after treatment stopped, and regained enough to leave a net 5.6% — roughly two thirds of the loss returned. That is a medication trial, and nothing here is medical advice about medication. But the shape of it applies to any long deficit: appetite and expenditure both push back, and “just stop” is not a plan. The maintenance instrument above turns the climb into weekly steps, holds each one long enough for the scale to answer, and never places a step below the intake floor.
Once you are at maintenance, recomposition is the option that gets oversold. It is real and well documented — including in people who already train, not only beginners — and the two variables that decide it are progressive resistance training and enough protein. The 1.6–2.2 g/kg anchor this site uses is not a round number somebody liked: a meta-regression of 49 studies put the point beyond which extra protein stopped adding lean mass at 1.62 g/kg/day, with a 95% confidence interval running from 1.03 all the way to 2.20. What the research does not support is the implication that recomposition works equally well for everyone. It is fastest for beginners, for people returning after a layoff, and for people carrying more fat; a lean, well-trained lifter should expect it to be slow, and the tool says so on the panel rather than in the small print.
Sources
- Wilding et al. (2022), Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension, Diabetes, Obesity and Metabolism
- Barakat, Pearson, Escalante, Campbell & De Souza (2020), Body recomposition: can trained individuals build muscle and lose fat at the same time?, Strength and Conditioning Journal 42(5)
- Morton et al. (2018), A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength, British Journal of Sports Medicine
This calculator is an estimation tool, not medical advice. Calorie needs are affected by medical conditions and medications; for decisions that touch your health, a doctor or registered dietitian is the right resource.