How to work out your BMR and daily calories

Your body burns energy all day, even if you spend it on the sofa. The amount it needs just to keep you alive at rest is your basal metabolic rate, or BMR. Add the energy you use moving about, and you get an estimate of how many calories you need each day to stay at the same weight. This guide shows the formula step by step with two worked examples, explains the activity multipliers, compares the result with the NHS guideline amounts, and covers how to use the figure if you want to lose or gain weight. It is an estimate for general information, not medical advice, and anyone with a health condition should speak to a GP or dietitian.

By Valtrinity. Updated 18 October 2026.

What BMR is and what it is not

BMR is the energy your body uses at complete rest to power your heart, lungs, brain, temperature control and other basic functions. For most people it makes up the largest share of the day's energy use, often around 60 to 70 per cent of the total.

It is not the same as your total daily energy expenditure, which also includes the energy you spend on movement, exercise and digesting food. It is also not a precise measurement. Formulas estimate BMR from your sex, weight, height and age, and the true figure can differ by a few hundred calories from person to person.

Calories here means kilocalories, shortened to kcal. Food labels in the UK show energy in both kilojoules (kJ) and kilocalories, and one kilocalorie is 4.184 kilojoules.

The Mifflin-St Jeor formula

A widely used equation for adults is the Mifflin-St Jeor formula. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) minus (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) minus (5 × age in years) minus 161.

The result is in kilocalories per day. Use weight in kilograms and height in centimetres. If you know your weight in stones and pounds, convert first: 10 stone 7 pounds is 147 pounds, which is 66.7 kg. A height of 5 ft 5 is 65 inches, or 165.1 cm.

The formula gives a smooth, sensible estimate for most adults, but it does not know about your body composition. Someone with more muscle will burn more at rest than someone of the same weight with less.

Worked example 1: a woman aged 35

Take a woman who is 35 years old, 165 cm tall and weighs 65 kg. Weight term: 10 × 65 is 650. Height term: 6.25 × 165 is 1,031.25. Age term: 5 × 35 is 175. Now put them together: 650 plus 1,031.25 minus 175 minus 161 is 1,345.25.

Her BMR is about 1,345 kcal per day. That is what she would burn lying still for a day.

Now apply an activity level. If she is moderately active, exercising three to five days a week, the multiplier is 1.55, so her daily need is 1,345.25 × 1.55, which is 2,085 kcal. If she is lightly active, with a multiplier of 1.375, the figure is 1,850 kcal.

Worked example 2: a man aged 40

Take a man who is 40 years old, 180 cm tall and weighs 85 kg. Weight term: 10 × 85 is 850. Height term: 6.25 × 180 is 1,125. Age term: 5 × 40 is 200. For men, add 5. The total is 850 plus 1,125 minus 200 plus 5, which is 1,780.

His BMR is 1,780 kcal per day. With a sedentary lifestyle, such as a desk job and little exercise, the multiplier is 1.2, so he needs about 2,136 kcal. With moderate activity at 1.55, the figure is 2,759 kcal.

The two examples show why a single number for everyone is misleading. The same activity level gives answers more than 600 kcal apart, mostly because of differences in size, sex and age.

Activity multipliers

To turn BMR into an estimate of total daily energy use, multiply by an activity factor. The usual values are 1.2 for little or no exercise, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days a week, 1.725 for hard exercise six or seven days a week, and 1.9 for very hard exercise or a physically demanding job.

Most people overestimate their activity level. A job that involves sitting, plus three gym sessions a week, often fits the lightly active or moderately active band at most. If you are unsure, choose the lower one and see how your weight changes over a few weeks.

Treat the result as a starting point. The only way to find your real maintenance level is to track your intake and your weight over two to four weeks and adjust.

How this compares with NHS guidance

The NHS gives general guideline daily amounts for adults: about 2,500 kcal for men and about 2,000 kcal for women, to maintain a healthy weight. These are averages across a population. The worked examples above give 2,085 kcal for the woman and 2,759 kcal for the man at moderate activity, which are in the same range but not identical, because they take her and his own size and age into account.

Use the NHS figure as a sanity check. If a calculation gives you 1,000 kcal for maintenance, or 4,500, check your inputs, because both are unusual for most adults.

Needs vary through life. They tend to fall with age as muscle mass declines, and rise during pregnancy and breastfeeding. Children and teenagers have different requirements and should not use an adult formula.

Using the number for weight goals

To lose weight you need to eat less than you burn. The NHS suggests aiming to lose 0.5 to 1 kg (1 to 2 lb) a week, which for most people means eating about 600 kcal a day less than they use. For the woman in our example, whose maintenance is about 2,085 kcal, that would be about 1,485 kcal a day.

Do not go below your BMR for long periods without medical advice. For the same woman, 1,345 kcal is a floor, and heavy cuts can leave you tired, hungry and short of nutrients. Slow, steady change tends to be easier to keep up.

To gain weight, eat a little above maintenance, perhaps 250 to 500 kcal a day, and combine it with strength training if the aim is muscle. Whatever your goal, check progress every two weeks and adjust by about 100 to 200 kcal at a time, rather than making large changes.

Tools mentioned in this guide

Frequently asked questions