Learning the BMR formula is the quickest way to understand how many calories your body needs just to stay alive. BMR, or basal metabolic rate, is the energy used for breathing, keeping your heart beating, maintaining body temperature, and running all the basic processes that continue even when you are lying still. It is not the same as the calories you burn in a full day, because it leaves out movement and exercise, but it is the foundation every daily calorie estimate is built on.
Once you can work out your BMR by hand, activity levels, weight-loss targets, and diet plans all make much more sense, because you can see exactly where each number comes from. This guide explains the formula term by term, walks through the steps in order, and finishes with a full worked example. To check your own number in seconds, use our free BMR Calculator.
The Formula
The tool uses the Mifflin-St Jeor equation, which is the formula most commonly used to estimate BMR. It has one version for men and one for women, and both give the answer in kilocalories per day. For men, BMR = 10 x weight in kilograms + 6.25 x height in centimetres – 5 x age in years + 5. For women, BMR = 10 x weight in kilograms + 6.25 x height in centimetres – 5 x age in years – 161.
Each term has a clear job. The weight term, 10 times weight in kilograms, is the largest part for most people, because a larger body needs more energy simply to maintain itself. The height term, 6.25 times height in centimetres, adds a smaller amount for body size. The age term is subtracted, because resting energy needs tend to fall as we get older, largely as muscle mass declines. The final number is the sex adjustment: plus 5 for men, or minus 161 for women, reflecting the average difference in body composition between the sexes.
Notice what the formula does not include: it does not ask about exercise, job, or daily steps. That is deliberate. BMR is the resting figure only, so it stays the same whether you spend the day at a desk or on your feet. Activity is added afterwards, when BMR is turned into a total daily figure, which is why confusing the two is the most common mistake people make with this calculation.
How to Calculate BMR Step by Step
- Write down your sex, age in years, weight in kilograms, and height in centimetres. Convert first if you normally weigh yourself in pounds or measure height in inches, because the formula only works with metric units.
- Multiply your weight by 10. This is the weight term, and it is usually the biggest number in the calculation.
- Multiply your height by 6.25, then add it to the weight term. Work slowly here, because a misplaced decimal is the most common source of a wrong answer.
- Multiply your age by 5 and subtract it from the running total. This is the age adjustment, and it is why BMR falls gradually over the years.
- Apply the sex adjustment last: add 5 for men, or subtract 161 for women. The result is your BMR in kilocalories per day.
Keep each term separate on paper or in a calculator, rather than trying to do the whole sum in your head. Checking the terms one at a time makes an error much easier to spot, and the same method works for anyone, whatever their size or age.
Worked Example
Take a man aged 30, weighing 70 kg, and measuring 175 cm. Using the Mifflin-St Jeor formula for men: BMR = 10 x 70 + 6.25 x 175 – 5 x 30 + 5. Working term by term, 10 x 70 = 700, 6.25 x 175 = 1,093.75, and 5 x 30 = 150. So BMR = 700 + 1,093.75 – 150 + 5 = 1,648.75, which is 1,649 kcal per day.
For comparison, a woman with the same age, weight, and height would use minus 161 instead of plus 5, giving 700 + 1,093.75 – 150 – 161 = 1,482.75, or about 1,483 kcal per day. The gap of 166 kcal is entirely the sex adjustment, which shows why using the right version of the formula matters. Remember, both figures are resting values: neither includes the calories burned by moving, working, or exercising during the day.
Common Mistakes / Good to Know
- Using pounds and inches: the formula needs kilograms and centimetres, so convert first, or every term will be wrong.
- Mixing up BMR and total daily calories: BMR is rest only, so eating at your BMR while active usually creates a deficit, even though it may feel like a maintenance amount.
- Using the wrong sex adjustment: plus 5 for men and minus 161 for women is a 166 kcal difference, which is enough to change a diet plan.
- Treating the result as exact: BMR is an estimate for an average person, so use it as a starting point and adjust from real weight trends over a few weeks.
It also helps to recalculate after a large weight change, because BMR falls as body weight falls. A figure worked out a year ago may no longer match your body today, especially after a long diet or a big change in muscle mass.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR is the calories your body burns at complete rest. TDEE is BMR multiplied by an activity factor, so it includes all daily movement and exercise and is the maintenance calorie figure.
Why is BMR lower for women than for men?
The formula uses minus 161 for women and plus 5 for men, a difference of 166 kcal. This reflects the average difference in body composition, since muscle tissue uses more energy at rest than fat tissue.
Should I eat at my BMR to lose weight?
Usually not as a fixed rule. Most active people burn more than their BMR, so eating at BMR creates a deficit, but a safer starting point is your total daily expenditure minus a modest amount, adjusted from weight trends.
How often should I recalculate my BMR?
Recalculate after a noticeable weight change, a birthday that moves you into a new age year, or a big change in muscle mass. Otherwise, a review every few months is enough, because daily fluctuations do not change your true average.
Once you know your resting figure, the next step is to turn it into a full-day total. Use our TDEE Calculator to add your activity level to this BMR.
For the activity multipliers and a full daily example, read How to Calculate TDEE: Formula, Multipliers and Example.
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