BMR Calculator guide
BMR Calculator: Your Basal Metabolic Rate Explained
Use our BMR calculator to work out how many calories your body burns at rest, with the Mifflin-St Jeor, Harris-Benedict and Katch-McArdle equations.
By the AllCalculator editorial teamUpdated 16 October 20262 min read
Even when you're asleep, your body burns energy to keep your heart beating, your lungs breathing and your cells working. That's your basal metabolic rate (BMR), and for most people it's well over half of the calories they burn in a day. Our BMR Calculator works it out.
How to use the calculator (BMR Calculator)
- Choose your sex and enter your age.
- Enter your weight and height in kilograms and centimetres, or stones and feet.
- If you know it, add your body fat percentage for an extra estimate.
You'll see your BMR and a table of how many calories you need a day at different activity levels.
The formulas
- Mifflin-St Jeor (the main result): 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women. It's the most accurate of the common equations for most people.
- Revised Harris-Benedict: an older equation, updated in 1984. It usually gives a slightly higher figure.
- Katch-McArdle: 370 + 21.6 × lean body mass in kg. It's useful for very lean or muscular people, because it uses your lean mass rather than your weight.
BMR and TDEE
Your BMR is what you'd burn lying still all day. Your total daily energy expenditure (TDEE) adds everything else: walking, working and exercise. It's worked out by multiplying your BMR by an activity factor, from 1.2 if you're inactive to 1.9 if you're very active.
A worked example
With the calculator's default settings, a 35-year-old woman who is 168cm tall and weighs 70kg has a BMR of about 1,410 kcal a day. If she does light exercise 1 to 3 days a week, she needs about 1,940 kcal a day to maintain her weight.
Frequently asked questions
Can I raise my BMR?
Building muscle through strength training helps a little, because muscle uses more energy than fat. Your BMR also falls slowly with age and when you lose weight.
Should I eat less than my BMR to lose weight?
It's not usually recommended. Aim for a modest deficit from your TDEE instead, and talk to your GP before trying a very low-calorie diet.
How accurate is it?
For most people, Mifflin-St Jeor is within about 10% of a measured BMR. Your actual figure depends on genetics, health and body composition.
To plan what to eat each day, try our Calorie Calculator and Macro Calculator.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.