Calorie Calculator
Free calorie calculator to estimate your daily calorie needs and BMR. Find out how many calories you need to maintain, lose, or gain weight based on your age, weight, height, and activity level.
Which equation this uses, and why
Basal metabolic rate cannot be measured without a lab, so calculators predict it from a regression fitted to people who were measured. Three equations dominate. Run on the same person — a 35-year-old man, 80 kg, 178 cm — they disagree by nearly 100 kcal:
| Equation | BMR | Inputs | Notes |
|---|---|---|---|
| Mifflin-St Jeor1990 | 1,743 | Age, sex, height, weight | Used here. Most accurate of the three for the general population. |
| Harris-Benedict1919, rev. 1984 | 1,816 | Age, sex, height, weight | Older, and tends to read high — it predates modern body composition. |
| Katch-McArdle1996 | 1,839 | Lean body mass | Best if you know your body fat percentage, since it ignores fat mass. |
Mifflin-St Jeor
Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161W = weight in kg · H = height in cm · A = age in years
Note the only difference between the two lines is a constant. The equation does not model sex beyond that offset, which is one reason it is a starting estimate rather than a measurement.
The activity multiplier is where the error lives
BMR is the stable part. Your total daily energy expenditure is BMR times an activity factor, and that factor swings the answer by more than a thousand calories on the same body:
| Factor | Level | Looks like | Daily total |
|---|---|---|---|
| ×1.2 | Sedentary | Desk job, little deliberate exercise | 2,091 kcal |
| ×1.375 | Light | Light exercise 1–3 days a week | 2,396 kcal |
| ×1.55 | Moderate | Moderate exercise 3–5 days a week | 2,701 kcal |
| ×1.725 | Very active | Hard exercise 6–7 days a week | 3,006 kcal |
| ×1.9 | Extra active | Physical job, or twice-daily training | 3,311 kcal |
Sedentary to extra active is a 1,220 kcal spread — bigger than the gap between any two BMR equations, and bigger than most people’s intended deficit. Most people also overestimate here. Three gym sessions a week alongside a desk job is light, not moderate; the multiplier is meant to cover the whole week, including the days you sit still.
The 500-calorie rule, and where it breaks
The familiar advice — cut 500 kcal a day to lose about a pound a week — comes from the estimate that a pound of body fat stores roughly 3,500 kcal. It is a reasonable starting point and a poor long-term model.
It fails because the target moves. As you lose weight there is less of you to carry, so both BMR and the cost of movement fall; a smaller body simply needs less. On top of that, energy expenditure adapts downward during a sustained deficit by more than size alone explains. The practical result is that a fixed deficit produces fast early loss that flattens out — which reads as failure but is arithmetic.
What to do instead: treat the number as a hypothesis. Hold intake steady for two to three weeks, track weight, and adjust from the trend rather than from the prediction. Your own data beats any equation within a month.
Floors worth respecting
A bigger deficit is not proportionally better. Below roughly 1,200 kcal for women and 1,500 for men — the figures commonly used in clinical guidance — it becomes hard to meet protein and micronutrient needs from food alone, and more of the loss comes from lean tissue rather than fat.
- Aim for 0.5–1% of body weight per week. Faster loss mostly costs muscle and is harder to hold onto.
- Keep protein up in a deficit. Roughly 1.6–2.2 g per kg of body weight is the range repeatedly associated with preserving lean mass while losing fat.
- Resistance training changes what you lose, not just how much — it is the main lever for keeping muscle through a cut.
When an estimate is not enough
These equations were fitted to healthy adults. They do not account for pregnancy or breastfeeding, thyroid conditions, diabetes, eating disorders, or medications that alter appetite or metabolism. If any of those apply, or you are planning a large or prolonged deficit, the number on this page is a conversation starter for a clinician or a registered dietitian — not a plan.
How wrong can the estimate be
Mifflin-St Jeor lands within 10% of measured BMR for most people, which still leaves a range of roughly ±170 kcal on a 1,700 kcal basal rate before the activity multiplier touches it. Two people with identical height, weight, age and sex genuinely differ, mostly through body composition: muscle is metabolically active, stored fat much less so.
That is why the Katch-McArdle equation exists — given a reliable body fat percentage it skips the proxies and works from lean mass directly. It is the better choice if you have a DEXA scan or a decent estimate, and worse than useless with a guessed number.
Intake is the other half, and it is measured more poorly than most people believe. Self-reported food intake is under-reported by a wide margin in study after study, often by 20% or more, and it is not deliberate — it is oil in the pan, drinks, and portion sizes. If the scale disagrees with your log, the log is the more likely suspect.