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Calorie Calculator

This estimates how many calories your body uses in a day, using the Mifflin-St Jeor equation — the formula most commonly recommended for general-population estimates. The equation is named here because different formulas give different answers, and a number you cannot check is not much use.

Units
Sex

The equation was derived with a binary variable; see the notes below

Enter your age, weight and height to estimate your daily calories.

These are population estimates, not a plan

Individual metabolism varies by 10% or more from what any equation predicts, and the activity multipliers are broad brackets. Treat the number as a starting point, adjust based on what actually happens over a few weeks, and speak to a doctor or dietitian before making substantial changes — particularly if you are pregnant, breastfeeding, under 18, or managing a medical condition.

How to use this tool

  1. Choose metric or imperial units.
  2. Select the sex the equation should use — see the notes on what this means.
  3. Enter your age, weight and height.
  4. Pick the activity level that best matches a typical week, not your best week.
  5. Read your maintenance calories, with targets for losing or gaining weight underneath.

Formula and method

Basal metabolic rate (Mifflin-St Jeor)

men:   BMR = 10w + 6.25h − 5a + 5
women: BMR = 10w + 6.25h − 5a − 161
w
— weight in kilograms
h
— height in centimetres
a
— age in years

BMR is what your body uses at complete rest — keeping you breathing, warm and circulating. It is typically 60–70% of total daily use.

Total daily energy expenditure

TDEE = BMR × activity factor

The factors run from 1.2 for a sedentary week to 1.9 for a physical job or twice-daily training. They are broad brackets, which is the largest source of error in the whole estimate.

Worked examples

A 30-year-old man, 80 kg, 180 cm, moderately active

  1. BMR: 10(80) + 6.25(180) − 5(30) + 5 = 1,780
  2. TDEE: 1,780 × 1.55 = 2,759

About 2,759 kcal a day to maintain weight.

The same figures for a woman

  1. BMR: 10(80) + 6.25(180) − 5(30) − 161 = 1,614

About 2,502 kcal a day — the 166 kcal gap is the constant in the equation.

Notes and limitations

  • These are population averages. Individual metabolic rate varies by 10% or more from what any equation predicts, so treat the number as a starting point and adjust based on what actually happens over several weeks.
  • The activity multiplier is the least precise part. People consistently overestimate their activity level; choosing the bracket below the one you first pick is often more accurate.
  • The Mifflin-St Jeor equation was derived using a binary sex variable and does not account for body composition. Athletes and people with high muscle mass will be under-estimated — the Katch-McArdle formula, which uses body fat percentage, suits them better.
  • The 500 kcal deficit for roughly 0.5 kg a week is a long-standing rule of thumb, not a precise physiological law. Weight loss slows as you get lighter, because a smaller body uses fewer calories.
  • This is not medical or dietary advice. It is not appropriate for children, and anyone who is pregnant, breastfeeding, or managing a medical condition should speak to a doctor or dietitian rather than relying on a calculator.

Frequently asked questions

How many calories do I need a day?

It depends on your size, age, sex and how active you are. Enter your details above for an estimate. Most adults land somewhere between 1,600 and 3,000 kcal, but the range is wide and personal.

What is the difference between BMR and TDEE?

BMR is what you burn at complete rest, keeping your body running. TDEE adds everything else — moving, working, exercising, even digesting — and is the figure that matters for planning what to eat.

Which formula does this use, and why?

Mifflin-St Jeor. It was published in 1990 and has been found more accurate for modern populations than the older Harris-Benedict equation, which tends to over-estimate. The two can differ by 100 kcal or more for the same person, which is why the formula is named on the page.

How do I lose weight using this number?

Eat below your maintenance figure. A deficit of about 500 kcal a day corresponds to roughly 0.5 kg a week for many people. Larger deficits are harder to sustain and cost more muscle, and the rate slows as you get lighter.

Should I eat back the calories I burn exercising?

If you selected an activity level that already reflects your training, exercise is counted and adding it again would double-count. Fitness trackers also tend to over-report calories burned, sometimes substantially.

Is this accurate for athletes?

Less so. The equation does not know your body composition, and muscle uses more energy at rest than fat. If you know your body fat percentage, the Katch-McArdle formula will give a closer estimate.

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