BMR calculator
This calculator works out Basal Metabolic Rate, the calories the body burns at complete rest, from height, weight, age and sex, using the Mifflin-St Jeor equation. It also shows two rough daily totals once a sedentary or moderate activity level is added. Figures are general estimates rather than medical advice.
How is BMR calculated?
Basal Metabolic Rate is calculated with the Mifflin-St Jeor equation, which is the biggest single slice of daily energy use.
For men, the sum is ten times weight in kilograms, plus 6.25 times height in centimetres, minus five times age, plus five.
For women, the final step subtracts 161 instead of adding five, reflecting the average difference in body composition.
BMR alone excludes movement, so multiplying it by an activity factor gives Total Daily Energy Expenditure, the number a calorie plan is normally based on.
| Activity level | Multiplier applied to BMR |
|---|---|
| Sedentary | x1.2 |
| Moderately active | x1.55 |
| Very active or hard training | up to x1.9 |
What would this look like for an example person?
Take a 30-year-old woman who is 165 cm tall and weighs 65 kg.
The Mifflin-St Jeor equation gives (10 x 65) plus (6.25 x 165) minus (5 x 30) minus 161.
That sum is 650 plus 1,031 minus 150 minus 161, which comes to a BMR of about 1,370 kcal a day.
On a fairly sedentary day that points to roughly 1,644 kcal to maintain weight, rising to about 2,124 kcal if moderately active through the week.
Common questions
What is BMR?
Basal Metabolic Rate is the number of calories your body uses at complete rest just to keep you alive: breathing, circulation, keeping warm and repairing cells. It is the largest single part of the calories you burn each day, before any movement is added.
How is BMR calculated?
This tool uses the Mifflin-St Jeor equation. For men it is ten times weight in kilograms, plus 6.25 times height in centimetres, minus five times age, plus five. For women the last term is minus 161. It is one of the more accurate simple equations for healthy adults.
What is the difference between BMR and TDEE?
BMR is what you burn at rest. Total Daily Energy Expenditure, or TDEE, is BMR multiplied by an activity factor to include everyday movement and exercise. TDEE is the figure to use when planning how much to eat; BMR is the resting baseline it is built on.
Why does BMR fall with age?
Muscle is more metabolically active than fat, and people tend to lose muscle and gain fat as they get older, so resting energy use drifts down. Staying active and keeping muscle through resistance exercise slows that decline.
Should I ever eat below my BMR?
Eating below BMR for long stretches is not recommended without medical supervision, because it can leave you short of nutrients and is hard to sustain. For weight loss, base a modest deficit on your TDEE, not your BMR.
What would this look like for an example person?
For a 30-year-old woman who is 165 cm tall and weighs 65 kg, the Mifflin-St Jeor equation gives a BMR of about 1,370 kcal a day. On a mostly sedentary day that points to roughly 1,644 kcal to maintain weight, rising to about 2,124 kcal if moderately active through the week. These figures are general estimates rather than medical advice.
Sources & Rate Verification
Rates verified against official statutory guidance on 6 September 2026.