Calorie Calculator
Estimate daily calories from the Mifflin-St Jeor equation, with macro splits.
An Estimate, And What It Is An Estimate Of
Two numbers matter here. The first is what your body uses at complete rest — breathing, circulating, keeping warm — which is most of your daily total for most people. The second is that figure multiplied by how active you are, which is what you would eat to stay the same weight.
Both come from the Mifflin-St Jeor equation, which is the one most dietitians use because it has held up better than the older Harris-Benedict formula. It is still an estimate for an average body: two people of the same height, weight, age and sex can differ by a few hundred calories a day. Use the result as a starting point to adjust from over a few weeks, not as a target to obey.
Key features
- Mifflin-St Jeor — the equation dietitians generally prefer, not the older Harris-Benedict.
- Metric or imperial — centimetres and kilograms, or feet, inches and pounds.
- Five activity levels — described by what you actually do rather than by a bare multiplier.
- Deficit and surplus targets — with a warning when a deficit drops below your resting needs.
- Three macro splits — balanced, higher protein and lower carbohydrate, in grams.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Calorie Calculator
- Enter your details
Age, sex at birth, height and weight. The equation is calibrated on sex at birth, which is why it asks. - Choose your activity level
Most people overestimate this. A desk job with three gym sessions is "light", not "moderate". - Read the four figures
Resting, maintenance, and targets for losing or gaining. - Adjust after a few weeks
Track your actual weight against the prediction and move the number to match reality.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Calculators |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
How accurate is this?
Mifflin-St Jeor lands within about 10% of measured resting metabolism for most people, which on a 2,000-calorie day is 200 calories either way. The activity multiplier is much rougher still. The practical approach is to eat at the estimate for two or three weeks, weigh yourself regularly, and adjust by 100 or 200 calories based on what actually happened.
Why does a deficit below my resting rate get a warning?
Because eating less than your body uses at complete rest is a different kind of decision from a moderate deficit, with real risks around nutrient intake and muscle loss, and it is not something to start on the strength of a web page. A smaller deficit takes longer and is far easier to stick to, which is usually what actually determines the outcome.
Why 500 calories a day for half a kilo a week?
A kilogram of body fat stores roughly 7,700 calories, so half a kilo is about 3,850 — about 550 a day. The 500 figure is the familiar rounding of that. It is an approximation: the rate slows as you get lighter, because a smaller body uses less.
What is the right macro split?
For most goals it matters much less than the total. Protein is the one worth being deliberate about — enough of it preserves muscle in a deficit and helps with fullness. Beyond that, the split that you can actually keep to is the one that works.
Is this suitable for everyone?
No. The equation is for healthy adults. If you are pregnant or breastfeeding, under eighteen, an athlete in serious training, or managing a condition that affects metabolism or nutrition, the number to use is the one a doctor or registered dietitian gives you, not this one.