Entering numbers into a calorie calculator takes thirty seconds. Getting a result you can use takes a bit more care, mostly around one question: how active are you really? This guide covers each input and what to do with the answer. If you first want the difference between the two terms, read BMR vs TDEE.
What you need
Four things: your weight in kilograms, your height in centimetres, your age in years, and the sex used for the formula. The equation behind the BMR and TDEE Calculator is Mifflin-St Jeor (Mifflin et al., 1990), which uses a different constant for men (+5) and women (−161). Those constants reflect average differences in body composition, so choose the one that matches the body you are estimating for.
A full example
A 35-year-old man, 180 cm, 80 kg. BMR = 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 1,755 kcal a day. That is what his body would burn lying still.
His TDEE depends on how he lives. At the moderate setting (exercise three to five days a week) it is 1,755 × 1.55 = about 2,720 kcal. At sedentary it would be about 2,106, a difference of more than 600 kcal from the same body.
Choosing the activity level
- Sedentary (× 1.2): desk job, little deliberate exercise.
- Light (× 1.375): exercise one to three days a week.
- Moderate (× 1.55): exercise three to five days a week.
- Active (× 1.725): hard exercise six or seven days a week.
- Very active (× 1.9): hard training plus a physical job.
People overrate this. A 45-minute workout does not make a day “active” if the other 15 hours are spent sitting. When in doubt, pick the lower level and see how your weight behaves.
Turning the number into a plan
Treat TDEE as a starting estimate of maintenance, not a target to hit exactly. Eat around it for two to three weeks, weighing yourself under similar conditions each time. If your weight is steady, the estimate is about right. If it drifts, move your intake by 100 to 200 kcal and watch again. Big cuts are a job for a doctor or dietitian, especially if you have a medical condition, are pregnant, or are under 18.
Limits to remember
The equation was built from healthy adults, so it can be off for very muscular or very lean people, older adults and anyone with a thyroid or metabolic condition. The activity multipliers are rules of thumb rather than measurements. Expect the result to be right to within a few hundred calories, not to the calorie.
Frequently asked questions
Why does the calculator ask for sex?
The equation uses a different constant for men and women, reflecting average differences in body composition. It is an estimate for an average body of that type, so treat it as a starting point.
How often should I recalculate?
When your weight changes by several kilograms or your routine changes, for example you start training or take a more active job. Age changes the result slowly, so a yearly check is enough for that.
Is TDEE the same every day?
No. It is an average. A rest day and a long-run day differ, so judge your intake over a week rather than a single day.
Source: Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247. General information only, not medical or nutritional advice.