Calorie calculator
How many calories you burn in a day, and what to eat to maintain, lose or gain weight. Uses the Mifflin-St Jeor equation, and shows you the working.
The equation, and why this one
This uses Mifflin-St Jeor, published in 1990, which is the equation most dietetic guidance now prefers for people with a BMI in the normal range. The older Harris-Benedict equation tends to overestimate.
For men:
BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
For women:
BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
That gives your basal metabolic rate — what your body uses at complete rest, before you move at all. Multiplying by an activity factor gives total daily energy expenditure, which is the number you actually eat to.
The activity multipliers are the weak link
Worth being straight about: the BMR equation is derived from measurement, but the activity multipliers below are convention rather than precision. They are widely used and roughly right, and they are also the largest source of error in any calculator like this.
| Level | Typical week | Multiplier |
|---|---|---|
| Sedentary | Desk job, no deliberate exercise | 1.2 |
| Lightly active | 1–3 sessions | 1.375 |
| Moderately active | 3–5 sessions | 1.55 |
| Very active | 6–7 sessions | 1.725 |
| Extremely active | Physical job, or two sessions a day | 1.9 |
The gap between sedentary and very active is more than 500 calories a day for the same body. If you are unsure, pick the lower option and watch what actually happens to your weight over three weeks — your own results beat any multiplier.
Where the loss and gain figures come from
A kilogram of body fat stores roughly 7,700 calories. So losing half a kilo a week means a deficit of about 3,850 calories a week, or 550 a day. Gaining a quarter kilo a week means a surplus of about 275 a day — deliberately smaller, because a large surplus adds fat faster than muscle.
These are averages over weeks, not daily targets to hit exactly. Water weight moves by more than this from one day to the next.
Common questions
Why is my number different from my watch?
A watch measures movement and heart rate and estimates from those; this estimates from body size and a stated activity level. Both are approximations of the same quantity by different routes. If they disagree by 10–15%, that is normal.
Should I eat back exercise calories?
If you chose an activity level that already includes your training, then no — it is counted. Adding exercise on top of a multiplier that assumed it is the most common way people accidentally eat at maintenance while trying to lose.
Does this work if I am pregnant, under 18, or very muscular?
No. Pregnancy and adolescence change requirements in ways this equation does not model, and Mifflin-St Jeor is least accurate at the extremes of body composition. A very muscular person will usually need more than it says.
Is anything I enter here recorded?
No. Your age, sex, height, weight and activity level never leave the page — the Mifflin-St Jeor equation runs in your browser and there is no server to send them to. The trade-off is that reloading loses your figures, because storing nothing means storing nothing.