The Mifflin–St Jeor equation
The calculator first estimates your basal metabolic rate (BMR): the energy your body uses at complete rest. It uses the Mifflin–St Jeor equation, published in 1990. Dietetic bodies often recommend it as the most reliable of the common BMR formulas for healthy adults.
TDEE means total daily energy expenditure: the calories you burn in a normal day, including movement and digestion. Eating about your TDEE keeps your weight roughly steady. In imperial units, the calculator converts pounds to kilograms (× 0.45359237) and inches to centimetres (× 2.54) first.
Worked example
A woman aged 30, 165 cm tall, weighing 60 kg, who exercises lightly 2–3 times a week:
- BMR = 10 × 60 + 6.25 × 165 − 5 × 30 − 161 = 600 + 1,031.25 − 150 − 161 = 1,320 kcal.
- TDEE = 1,320.25 × 1.375 (lightly active) = 1,815 kcal a day.
- For mild weight loss she would aim for about 1,815 − 250 = 1,565 kcal. A 500 kcal deficit gives 1,315 kcal, which is close to the 1,200 kcal floor.
Activity factors
The activity factor scales BMR up to your real daily burn. This table shows the effect for a man aged 35, 178 cm and 80 kg, whose BMR is 1,742.5 kcal:
| Activity level | Factor | What it means | TDEE |
|---|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise | 2,091 |
| Lightly active | 1.375 | Light exercise 1–3 days a week | 2,396 |
| Moderately active | 1.55 | Moderate exercise 3–5 days a week | 2,701 |
| Very active | 1.725 | Hard exercise 6–7 days a week | 3,006 |
| Extra active | 1.9 | Very hard training, or a physical job plus exercise | 3,311 |
Most people overestimate how active they are. If you are unsure between two levels, choose the lower one.
Calories to lose or gain weight
The results table subtracts or adds a fixed amount from your TDEE:
- Mild loss (−250 kcal) and loss (−500 kcal): a common rule of thumb is that a 500 kcal daily deficit loses about 0.5 kg a week at first. Real loss slows over time, because a lighter body burns less.
- Mild gain (+250 kcal) and gain (+500 kcal): useful when building muscle with strength training. A smaller surplus means less of the gain is fat.
Don't go too low. Eating below about 1,200 kcal a day for women or 1,500 kcal a day for men makes it hard to get enough protein, vitamins and minerals. Only do it under medical supervision. The calculator marks any target below these levels.
Tips for using your number
- Treat it as a starting point. Any formula can be off by a few hundred calories for an individual. Eat at your target for 2–3 weeks, track your weight, then adjust.
- Recalculate as you change. Your BMR falls as you lose weight and as you age.
- Protein and sleep matter. Enough protein and good sleep help you keep muscle while losing fat.
To see where your weight sits for your height, use the BMI calculator.
This calculator gives general information only. It is not medical advice. Talk to a doctor or a registered dietitian before starting a diet, especially if you are pregnant, breastfeeding, under 18 or have a health condition.
Frequently asked questions
What is the difference between BMR and TDEE?
How many calories should I eat to lose weight?
How accurate is the Mifflin–St Jeor equation?
Why does the formula need my sex?
Should I eat back the calories I burn exercising?
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