BMR Calculator NHS

Estimate your basal metabolic rate (BMR) — the energy your body uses at rest — with the Mifflin-St Jeor equation. This is an independent UK calculator and is not an official NHS tool.

What is BMR?

Basal metabolic rate describes the energy required to maintain essential body functions at rest. In everyday online calculators, BMR and resting energy expenditure are often used closely, although strict laboratory definitions differ. Your total daily energy use is higher because movement, exercise and other activity add to resting expenditure.

How to use the calculator

Select the sex term required by the equation, then enter age, height in centimetres and weight in kilograms. Choose Calculate BMR to see an estimated number of kilocalories per day. Reset clears all inputs and the result.

Mifflin-St Jeor formula

This calculator uses the commonly simplified Mifflin-St Jeor equations: for men, (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5; for women, the same calculation minus 161 instead of adding 5. The original 1990 research developed a predictive equation for resting energy expenditure in healthy adults.

Worked example

For a 30-year-old man who is 180 cm tall and weighs 80 kg: (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = approximately 1,780 kcal/day at rest.

BMR versus TDEE

BMR is not a maintenance-calorie target. TDEE adds estimated activity expenditure to resting energy needs. If you want an estimate that includes activity, use the TDEE Calculator NHS rather than treating BMR as your full daily calorie requirement.

Accuracy and limitations

The equation provides a population-based estimate rather than a direct measurement. The original study included healthy adults aged 19 to 78. Results may be less appropriate for children, pregnancy, some illnesses, unusual body composition or circumstances that substantially alter metabolism. Indirect calorimetry is used when actual resting energy expenditure needs to be measured clinically.

Authoritative sources

• Mifflin et al. (1990), American Journal of Clinical Nutrition
• West London NHS Trust — understanding healthy body weight

Related calculators

NHS Calculator · TDEE Calculator NHS · Calorie Calculator NHS · Calorie Deficit Calculator NHS · BMI Calculator NHS

FAQs

Is this an official NHS BMR calculator?

No. It is an independent calculator using a published predictive equation.

Is BMR the number of calories I should eat?

No. BMR estimates resting expenditure only. Total daily requirements also depend on activity and other factors.

Why does the calculator ask for sex?

The published Mifflin-St Jeor equation contains sex-specific constants, so the calculator needs the corresponding input to apply that equation.

Can I use this during pregnancy?

The equation was not designed to estimate pregnancy energy requirements. Seek appropriate professional advice instead.

Medical disclaimer: This calculator provides an estimate for general information. It is not medical or dietetic advice and should not replace individual assessment by a qualified professional.