Calorie and BMR calculator
Resting burn and daily needs for adults
- Resting burn, BMR (kcal a day)
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A rough guide for healthy adults who are not pregnant or breastfeeding. It is not a personal diet plan.
Worked out in your browser. No sign-up.
This calorie calculator estimates your resting burn (BMR) with the Mifflin–St Jeor equation, then multiplies it by your activity level to show roughly how many calories keep your weight steady. Enter sex, age, height in centimetres and weight in kilograms. It works for adults aged 19 to 78 and is not meant for pregnancy or breastfeeding.
How it works
Resting burn = 10 × weight in kg + 6.25 × height in cm − 5 × age, then add 5 for men or take away 161 for women. That figure is multiplied by an activity factor between 1.2 (desk job, little exercise) and 1.9 (hard physical work or training twice a day).
Strictly speaking the equation estimates resting metabolic rate (RMR), but most apps call it BMR. Nobody measures your oxygen use here, so treat the result as a starting point. If you have picked an activity level that already includes your gym sessions, don't add the calories your watch shows for them on top.
Worked example
Tom is 30, 180 cm tall and weighs 80 kg. His resting burn comes out at 1,780 kcal. He works at a laptop all day and walks very little, so with the 1.2 factor he needs about 2,136 kcal to stay at 80 kg. On weeks when he trains three or four times, the moderate setting puts him nearer 2,759 kcal.
Real numbers can be a few hundred calories either side. Weigh yourself for two or three weeks and adjust.
Questions people ask
Should I eat my BMR?
No. BMR is roughly what your body uses lying still for a whole day. Walking, working and digesting food all burn extra, which is why the daily figure is always higher.
Which activity level should I pick for an office job?
Start with mostly sitting, even if you go to the gym a few times a week. One hour of exercise doesn't make the other 23 hours active. Move up a level only if your weight keeps dropping on that intake.
Why does my fitness watch give a different number?
Watches add their own guesses based on heart rate and steps. Neither the watch nor this formula measures what you actually burn, so a gap of 10 to 20% between them is normal.
Can I use it for a teenager?
No. The formula was built from adult data, and growing children need a different approach. Ask your GP or a paediatric dietitian instead.
Sources
- Mifflin et al., original study (1990) — checked 13.11.2026
- Texas HHS, activity factors — checked 13.11.2026
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Updated: 13 November 2026