Calorie Calculator
Estimate your daily calorie needs from age, sex, height, weight and activity using the Mifflin-St Jeor equation, with the error margins stated honestly.
Calories per day (estimated)
The dropdown you guess at outweighs everything you measure
For a 75 kg, 178 cm, 35-year-old man the basal figure is 1693. The activity selector then multiplies it:
| Setting | Multiplier | Result |
|---|---|---|
| Sedentary (little/no exercise) | 1.2 | 2,031 |
| Light (1–3 days/week) | 1.375 | 2,327 |
| Moderate (3–5 days/week) | 1.55 | 2,623 |
| Active (6–7 days/week) | 1.725 | 2,920 |
| Very active (hard exercise or physical job) | 1.9 | 3,216 |
The five multipliers are evenly spaced, 0.175 apart, so every click of the selector is the same 296 calories. The full span is 1,185 — 58% of the smallest figure on the list. Against that, twenty years of age moves the basal figure by 100 calories, about 6%. One click of the dropdown is worth three times two decades of ageing, and the full span is worth nearly twelve. "Three to five days a week" and "six to seven days" are not facts about you in the way your height is, and the difference between them dominates the calculation.
Which makes the goal buttons smaller than one click
The lose and gain figures move the maintenance number by 500. One step of the activity selector is 296 — 59% of it. So a deliberate 500-calorie deficit is more than undone by moving the selector up two notches. Put the other way round: if you are unsure whether you are "light" or "moderate", the uncertainty in your maintenance figure is well over half the entire deficit you were planning to run. The 500 is also absolute rather than proportional, so it is twice the percentage cut for someone maintaining on 1,600 as for someone maintaining on 3,200.
What each input is actually worth
Mifflin-St Jeor is 10 × kg + 6.25 × cm − 5 × age, plus an offset for sex. Every term is linear, so they trade at fixed rates that never change:
| One unit of | Is worth | Which equals |
|---|---|---|
| 1 kg of weight | 10 calories | 2 years of age |
| 1 cm of height | 6.25 calories | 0.625 kg, or 1.25 years |
| 1 year of age | -5 calories | 0.5 kg |
| The sex offset | 166 calories | 16.6 kg, or 33.2 years |
Gaining a kilogram exactly cancels two years of ageing, and four centimetres of height cancels five years. Those hold at every size, because nothing in the formula is proportional. The sex term is the odd one out: a flat 166 calories that never scales with anything, so it is under a tenth of a large basal figure and a considerably larger share of a small one. On its own it is worth 16.6 kg of body weight, or 33.2 years of age. None of which makes the estimate wrong. It makes it an estimate whose precision comes almost entirely from one dropdown, and worth revisiting if your training changes.
How to use
- Enter your age, sex, height and weight.
- Choose the activity level that matches your real week.
- Read your BMR and maintenance estimate.
- Adjust based on what actually happens over a few weeks.
Frequently asked questions
What is the difference between BMR and maintenance calories?
BMR is what your body uses at complete rest just to stay alive — breathing, circulation, cell repair. Maintenance is BMR multiplied by an activity factor to include movement, exercise and digestion. Maintenance is the figure that matters for eating; BMR is the floor it is built on.
Which equation does this use?
Mifflin-St Jeor, which research has repeatedly found to be the most accurate of the common predictive equations for the general population. The older Harris-Benedict equation tends to overestimate, and revisions of it are still widely quoted.
How accurate is the estimate?
Within about 10 per cent for most people, which on a 2,000-calorie requirement is a 200-calorie band. Individual metabolism varies more than any equation can capture, so the honest use of this number is as a starting point to adjust from, not a target to obey.
Which activity level should I pick?
Almost certainly a lower one than you think. Most people overestimate their activity, and the multipliers for the higher levels assume genuinely demanding training or physical work. Starting one level below your instinct, then adjusting from real results, tends to land closer.
How large a deficit is sensible for weight loss?
A moderate one. Very aggressive deficits are hard to sustain, cost muscle as well as fat, and frequently end in rebound. A deficit of a few hundred calories a day is slower and far more likely to be maintained. Anyone with a medical condition, or aiming at substantial weight change, should involve a clinician.
Why has my weight stopped changing?
Because requirements fall as weight falls — a lighter body costs less to move and maintain — and because people unconsciously become less active in a deficit. Recalculating at your current weight, and being honest about intake, usually explains the plateau.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.