Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest. It covers the basics that keep you alive: your heart beating, lungs working, brain running, and cells repairing themselves. If you stayed in bed all day and didn't move, BMR is roughly what you'd use.
It sounds technical, but it's the starting point for almost every calorie target, including the ones from our BMR calculator and calorie calculator.
The short answer
- BMR is the energy you burn at rest, typically somewhere between 1,300 and 1,900 kcal a day for UK adults
- It makes up the biggest share of what you burn in a day, but it is not your daily calorie target
- Your daily target is built from BMR plus activity. That total is called TDEE (see TDEE vs BMR)
How BMR is calculated
The most widely used formula is the Mifflin–St Jeor equation. It uses your weight, height, age and sex:
| Sex | Formula |
|---|---|
| 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 |
Example, a woman: Sarah is 35, 165 cm and 70 kg. (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 700 + 1,031 − 175 − 161 = about 1,395 kcal a day.
Example, a man: Tom is 42, 178 cm and 85 kg. (10 × 85) + (6.25 × 178) − (5 × 42) + 5 = 850 + 1,113 − 210 + 5 = about 1,758 kcal a day.
If you'd rather not do the sums, the BMR calculator does it instantly, in metric or stones and feet.
What affects your BMR
- Body size: a larger body needs more energy, even at rest
- Muscle mass: muscle burns more energy at rest than fat does, which is one reason men's BMR is often higher on average
- Age: BMR tends to drift down gradually through adult life, partly because muscle mass declines
- Genetics: two people of the same size can differ a little
- Hormones and health: thyroid conditions can raise or lower BMR, and pregnancy and breastfeeding increase energy needs. If you're concerned about your metabolism, speak to your GP
From BMR to daily calories
To estimate what you burn in a normal day, multiply your BMR by an activity factor:
| Lifestyle | Multiplier |
|---|---|
| Mostly seated (desk job, little exercise) | BMR × 1.2 |
| Lightly active (light exercise 1–3 days a week) | BMR × 1.375 |
| Moderately active (3–5 days a week) | BMR × 1.55 |
| Very active (6–7 days a week) | BMR × 1.725 |
Sarah, with a BMR of about 1,395 and a desk job, burns roughly 1,395 × 1.2 = 1,674 kcal a day. That figure, not her BMR, is her maintenance level. Our guide to how many calories to eat to lose weight shows how to set a sensible deficit from there.
Common misunderstandings
- "I should eat my BMR to lose weight." BMR is a floor to be aware of, not a plan. Start from your daily burn and take off a modest deficit instead
- "The number is exact." It's an estimate. Real BMR can differ from the formula by a few hundred calories either way, so treat it as a starting point and adjust based on how your weight changes over two to three weeks
- "I can boost my metabolism with a food or supplement." Evidence for this is weak. Staying active and keeping your muscle mass matters more, although the effect on BMR is modest
The bottom line
BMR is the energy your body uses at rest. It's worth knowing, but your day-to-day calorie needs are higher once movement is included. Work out your BMR, apply an activity factor, and use that as a starting point you can adjust with real-world results.
Sources: Mifflin–St Jeor equation (1990), NHS guidance on energy needs and healthy weight. This page is for general information and is not medical advice.