Fitness Calculators
Work out your BMI, resting calories, daily maintenance calories and macros. Simple forms, clear results, and every step shown so you can see how each number was made.
- are pregnant or breastfeeding
- are under 18
- have diabetes, kidney, liver, heart or thyroid conditions, or take medicines that affect weight or appetite
- have, or have had, an eating disorder
BMI calculator
Body Mass Index compares your weight with your height: weight in kg divided by height in metres squared. It is a quick screening number for adults, not a measure of health or body fat.
Your result will appear here.
Assumptions and limits
- Formula: BMI = weight (kg) / height (m)2.
- Categories follow the World Health Organization adult bands: under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 and over.
- Adult categories are not used for children and teenagers. Under 18s are compared with growth charts for their age and sex.
- BMI cannot tell muscle from fat, and does not show where fat is carried. Athletes and people with a lot of muscle can have a high BMI and be healthy.
- Some health bodies use lower cut-offs for people of South Asian background.
- BMI categories are not a reliable guide in pregnancy or while breastfeeding.
BMR calculator
Basal Metabolic Rate is the energy your body uses at complete rest. We use the Mifflin-St Jeor equation, for adults aged 18 and over.
Your result will appear here.
Assumptions and limits of the Mifflin-St Jeor equation
- Male:
10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 - Female:
10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161 - It was worked out from measurements of healthy adults at rest, mainly aged about 19 to 78. It is less reliable outside that range.
- It uses only weight, height, age and sex. It cannot see your muscle, body fat, hormones, thyroid health, medicines or genetics, which all change real energy use.
- The two versions come from studying men and women as groups. Sex here means the groups used in that research, not a statement about anyone. If neither version fits you, choose "Prefer not to say" to see a range, or use a BMR measured or estimated by a health professional.
- It is an average for people like you. Your own value can be higher or lower by a few hundred calories.
- Not for under 18s, and not for pregnancy or breastfeeding.
Daily maintenance calories (TDEE)
Total Daily Energy Expenditure is your BMR multiplied by an activity factor. It estimates the calories that would keep your weight steady.
Your result will appear here.
Assumptions and limits
- TDEE = BMR x activity factor. Factors used: 1.2, 1.375, 1.55, 1.725 and 1.9.
- BMR comes from the Mifflin-St Jeor equation above, or from the BMR you type in.
- Activity factors are rounded averages. People who think they are "moderately active" often differ a lot, so pick the level that matches an ordinary week.
- The result is approximate. Use it as a starting point and watch how your body responds over a few weeks.
- This page shows maintenance only. It does not prescribe weight-loss or weight-gain targets.
- Not for under 18s, and not for pregnancy or breastfeeding.
Macronutrient calculator
Turn a daily calorie target into grams of protein, carbohydrate and fat. You choose the target and the split. We do the maths and check the percentages add up to 100.
Your result will appear here.
Assumptions and limits
- Protein 4 kcal per gram, carbohydrate 4 kcal per gram, fat 9 kcal per gram.
- Grams = calories x percentage / kcal per gram. Percentages must add up to 100.
- This splits a target you choose. It does not decide what your target should be.
- Alcohol, fibre and food label rounding mean real meals will not match exactly.
- Not for under 18s. People with diabetes, kidney, liver or heart conditions, or an eating disorder history, should get a plan from a professional.
Questions about the calculators
Are these calculators medical advice?
No. They give general estimates from standard formulas. They cannot diagnose anything or replace a doctor, midwife or registered dietitian.
Why does the page ask for my age before calculating?
Adult BMI categories and the Mifflin-St Jeor equation are designed for adults. For under 18s we show a BMI number with no category and we do not give calorie or macro targets, because growing bodies need individual advice.
Why is sex asked for BMR and TDEE?
The Mifflin-St Jeor equation has one version for men and one for women, based on the groups studied. It cannot account for body composition, hormones or medical treatment. If you prefer not to say, you will see both results as a range, or you can type a BMR you already know.
How accurate is the calorie estimate?
It is a starting point. Real energy use differs between people of the same age, size and sex, and changes from day to day. Use the number for a few weeks, watch what happens to your weight and energy, and adjust with professional advice if needed.
Do the macro percentages have to add up to 100?
Yes. The calculator checks this and tells you how far off you are. Protein and carbohydrate count 4 kcal per gram and fat counts 9 kcal per gram.
Is my information saved or sent anywhere?
No. Everything is worked out inside your browser on your device. Nothing you type here is sent to us or stored.
General information only. Results are estimates and do not replace advice from a qualified health professional.