BMR Calculator (Basal Metabolic Rate)

Your body burns calories every second of the day, even while you are completely still, just to keep essential systems running: your heart beating, your lungs breathing, your organs functioning and your body temperature regulated. This baseline calorie burn is called your Basal Metabolic Rate, or BMR, and it forms the foundation for understanding your wider daily energy needs.

How to use the BMR calculator

Enter your gender, age, height and weight, in metric or imperial units, and choose which formula you would like to use: Mifflin-St Jeor or Harris-Benedict. The calculator shows your BMR in calories per day using your chosen formula, alongside the result from the other formula for comparison, so you can see how much the two methods differ for your own measurements.

BMR on its own is a useful reference point, but most people find it more practical alongside their Total Daily Energy Expenditure (TDEE), which adds an activity multiplier on top of BMR to estimate calories burned across a whole day, including exercise and general movement. Our TDEE calculator uses the same underlying BMR calculation and takes that extra step.

The BMR formulas explained

The Mifflin-St Jeor equation, published in 1990, is the formula most widely recommended by dietitians today:

• Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

The Harris-Benedict equation, in its revised 1984 form, is the older and still widely known alternative:

• Men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)
• Women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)

Both formulas rely on the same four measurements, but weight each one slightly differently. Harris-Benedict was built on a smaller, century-old dataset and tends to estimate somewhat higher than Mifflin-St Jeor for most people, which is part of why the newer formula has become the more commonly recommended option.

Worked example

Take a woman aged 30, 165cm tall, weighing 65kg.

Using Mifflin-St Jeor: (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 1,370 kcal a day.

Using Harris-Benedict: 447.593 + (9.247 × 65) + (3.098 × 165) − (4.330 × 30) = around 1,430 kcal a day.

The two formulas differ by about 60 calories a day for this example, a gap that is fairly typical, though it can be larger for people at higher weights or older ages. Neither figure is your total daily calorie need. Both are only the energy your body would burn at complete rest, with no activity added at all.

Common mistakes to avoid

The most common mistake is treating BMR as if it were a daily calorie target to eat. It is not: it is the minimum your body would burn lying still all day, and almost everyone burns meaningfully more than this once normal daily activity is included. Use our TDEE calculator for a more realistic daily figure that accounts for your actual activity level.

It is also worth remembering that both formulas are population averages, built from studying groups of people rather than measuring you individually. Your true metabolic rate can be somewhat higher or lower than either formula suggests, particularly if you carry more muscle than average, since muscle burns more calories at rest than fat tissue, which neither formula measures directly.

Finally, avoid making large, sudden changes to your diet based purely on a BMR estimate. These figures are a helpful starting point for a conversation about your goals, not a precise medical measurement. If you have specific weight or health goals, it is worth speaking to your GP or a registered dietitian, who can take a fuller picture of your health into account.

Related calculators

For your full daily calorie needs including activity, try our TDEE calculator, which builds on this same BMR calculation. Our BMI calculator and ideal weight calculator offer other ways to think about a healthy weight range for your height. Our healthy BMI guide covers NHS weight categories in more depth if you want further context.