BMR Calculator
Find the calories your body burns at complete rest — your basal metabolic rate.
BMR calculator
Uses the Mifflin-St Jeor equation, the one a 2005 review found most reliable.
What is BMR?
Your basal metabolic rate (BMR) is the calories your body burns at complete rest — the energy for your heart, lungs, brain and warmth. It is the largest part of most people's daily burn (for the worked example, 51 to 66% depending on activity). This calculator uses the Mifflin-St Jeor equation.
How this calculator works
Your BMR comes from the Mifflin-St Jeor equation, written out as 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, and the same with − 161 in place of + 5 for women. You give it your sex, age, height and weight — no activity level, because resting burn doesn't include movement.
BMR counts only the energy your body spends at rest — running your organs, holding your temperature steady and repairing tissue. It leaves out the calories you burn digesting food and the calories you burn moving; add those and you get your total daily burn instead.
One limitation is built in: the equation uses only your height, weight, age and sex, so it can't see body composition. Two people of the same size can have different resting burns if one carries more muscle, and the formula gives them the same number. For most people it is close enough to start from and then adjust from real weigh-ins.
Mifflin and colleagues built the equation from measurements of 498 healthy adults aged 19 to 78, both normal-weight and people with obesity (Mifflin et al. 1990). It replaced the older 1919 Harris-Benedict equations, which in Mifflin's own data overestimated measured resting burn by about 5%.
In a 2005 systematic review, Mifflin-St Jeor predicted resting burn within 10% of measured for more people than any other common equation — though individual errors can be larger, and older adults and US ethnic minorities were underrepresented in the data (Frankenfield et al. 2005).
Worked example
Take a 35-year-old man, 5 ft 10 in (178 cm), 185 lb (83.9 kg). His BMR is about 1,780 calories a day — the energy he would burn lying still for 24 hours.
As a share of his whole-day burn (TDEE), BMR shrinks as activity rises:
| Activity level | TDEE | BMR share |
|---|---|---|
| Inactive | 2,713 | 66% |
| Low active | 2,932 | 61% |
| Active | 3,120 | 57% |
| Very active | 3,482 | 51% |
At the same height and weight, his BMR falls with age — about 50 calories a day per decade:
| Age | 25 | 35 | 45 | 55 | 65 | 75 |
|---|---|---|---|---|---|---|
| BMR | 1,830 | 1,780 | 1,730 | 1,680 | 1,630 | 1,580 |
Nothing about his body changes across that row except the number in the age box — yet his estimated resting burn keeps dropping, which is part of why the same diet gets harder to hold as the years pass.
Typical BMR
BMR for some common starting points, at age 40:
| Person | BMR |
|---|---|
| Woman 5 ft 4 in, 150 lb | 1,335 |
| Woman 5 ft 4 in, 180 lb | 1,471 |
| Woman 5 ft 4 in, 210 lb | 1,608 |
| Man 5 ft 10 in, 180 lb | 1,733 |
| Man 5 ft 10 in, 220 lb | 1,914 |
| Man 5 ft 10 in, 260 lb | 2,096 |
And how BMR falls with age at a fixed size:
| Person | 25 | 40 | 55 | 70 |
|---|---|---|---|---|
| Woman 5 ft 4 in, 160 lb | 1,456 | 1,381 | 1,306 | 1,231 |
| Man 5 ft 10 in, 190 lb | 1,853 | 1,778 | 1,703 | 1,628 |
Calculated with the Mifflin-St Jeor equation.
BMR, RMR and TDEE
BMR is measured under strict resting conditions — overnight fasted, awake but completely still, in a thermally neutral room. RMR (resting metabolic rate) is measured under slightly looser conditions, so it tends to come out a touch higher. In practice the two numbers are close, and the terms are often used interchangeably — this calculator reports the Mifflin-St Jeor estimate for both.
Most "BMR calculators" online — this one included — actually report an RMR-style estimate, because a true BMR needs an overnight stay in a lab. The Mifflin-St Jeor equation was validated against measured resting metabolism, so the figure here is a practical resting estimate rather than a laboratory BMR.
TDEE is the whole day: your resting burn plus the energy for digesting food and for every movement. BMR is the floor it is built on. To see your whole-day number, use the TDEE calculator.
Should you eat your BMR to lose weight?
A popular rule says to eat your BMR to lose weight, but for most people that cuts too hard. For the worked example (low active), eating his BMR would leave a deficit of about 1,150 calories a day — more than the 500 to 1,000 a day Harvard Health describes for a 1 to 2 lb-a-week pace.
Very large deficits are also hard to sustain, and they tend to cost you muscle alongside fat — which lowers your resting burn further. A steadier gap below your whole-day burn, not your resting burn, is easier to hold and leaves room to eat enough protein and food you actually enjoy.
Whatever target you choose, don't eat below 1,200 calories a day (women) or 1,500 (men) without a health professional's supervision (Harvard Health Publishing). To turn a sensible deficit into a day-by-day plan and a year-long projection, use the calorie deficit calculator. It starts from your whole-day burn, applies a deficit you choose, and shows how your weight is likely to change over the months that follow.
Frequently asked questions
What is a good BMR?
There's no "good" BMR; it mostly reflects your body size, age and sex. A bigger or younger body burns more at rest, and that isn't better or worse — it just means you need more fuel.
How do I calculate my BMR?
Use the Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then + 5 for men or − 161 for women. For the worked example that comes to about 1,780 a day.
Does BMR decrease with age?
Yes — by the equation, about 50 calories a day for every decade at the same size. The worked example drops from 1,830 at 25 to 1,580 at 75.
How many calories do I burn doing nothing?
About your BMR — the resting energy for your heart, lungs and warmth. For the worked example that's about 1,780 a day.
Is BMR the same as RMR?
Nearly. BMR is measured under stricter resting conditions than RMR, but the numbers are close and the two terms are often used interchangeably.
Sources
- Mifflin MD et al., American Journal of Clinical Nutrition 1990
- Frankenfield D, Roth-Yousey L, Compher C, Journal of the American Dietetic Association 2005
- National Academies (2023), Dietary Reference Intakes for Energy, Table S-1
- National Academies (2023), chapter 7, activity levels
- Harvard Health Publishing, Calorie counting made easy