BMR Calculator

What BMR is

Your Basal Metabolic Rate is the number of calories your body burns just to keep you alive at complete rest — powering your heart, brain, breathing, body temperature and constant cell repair. It is measured over a full day and assumes you are awake, lying still and have not eaten recently. For most people, BMR is the single largest chunk of daily energy use, often 60–70% of the total, so it is the natural starting point for understanding how many calories you need.

BMR is closely related to two other terms you may see. Resting Metabolic Rate (RMR) is measured under slightly less strict conditions and comes out a little higher, but the two are often used interchangeably. Your Total Daily Energy Expenditure (TDEE) is the bigger number that includes everything you do on top of resting — walking, working, exercising and even digesting food.

How BMR is calculated

This calculator uses the Mifflin-St Jeor equation, published in 1990 and repeatedly found in research to be among the most accurate predictive formulas for healthy adults. It combines your weight, height, age and sex. The formula is slightly different for men and women:

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161

The only difference between the two is the final constant: men add 5, women subtract 161. That single term reflects the average difference in body composition between the sexes. If you enter your measurements in imperial units, the calculator converts them to kilograms and centimetres first, then applies the same equation, so the result is identical either way.

An older alternative you may come across is the Harris-Benedict equation, first published in 1919 and revised in 1984. It uses the same four inputs but different coefficients, and it tends to estimate BMR slightly higher than Mifflin-St Jeor. Both are respected, but most modern dietitians favour Mifflin-St Jeor because studies have shown it predicts measured resting energy more closely across a general population.

What each input means

• Age. Entered in years. BMR falls gradually as you get older, so age lowers the estimate. The equation is designed for adults and is not appropriate for children.
• Sex. Male or female, used to pick the +5 or −161 constant above. On average men carry more muscle, which burns more energy at rest, so the male figure comes out higher for the same height and weight.
• Height. Enter it in centimetres (metric) or feet and inches (imperial). Taller bodies have more tissue to maintain, so greater height raises BMR.
• Weight. Enter it in kilograms (metric) or pounds (imperial). Weight has the strongest effect of any input, because a larger body simply needs more energy to keep running.
• Units. The Metric / Imperial switch only changes how you type your numbers in. Behind the scenes everything is converted to metric before the calculation, so both settings give the same BMR.

BMR vs TDEE

BMR alone is not a number you should eat at, because you never actually spend a whole day at complete rest — you get up, move around and exercise. To turn BMR into your real daily burn, you multiply it by an activity factor. The result is your TDEE, or Total Daily Energy Expenditure: the calories you burn in a normal day. The table above the article shows your BMR scaled across four common activity levels so you can see the range at a glance.

Once you know your TDEE, you can set a goal. Eating roughly at your TDEE keeps weight steady; eating below it creates the deficit needed to lose weight; eating above it supports weight or muscle gain. To work out specific calorie targets toward a goal, use the calorie / TDEE calculator. If you are still unsure which figure applies to you, BMR vs TDEE explained walks through the difference in plain language.

Worked example

Here is an illustrative example — not a recommendation for any real person. Suppose a 30-year-old woman is 165 cm tall and weighs 65 kg. Using the women's Mifflin-St Jeor formula:

BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161
BMR = 650 + 1031.25 − 150 − 161
BMR ≈ 1,370 kcal per day

That figure is what her body would use at complete rest. To estimate a normal day, she multiplies by an activity factor. If she is lightly active (× 1.375), her TDEE is about 1,884 kcal; if moderately active (× 1.55), about 2,124 kcal. The same steps apply to any set of numbers — swap in your own age, height and weight and the calculator does the arithmetic for you.

Activity multipliers

Activity factors are the standard multipliers used to move from BMR to TDEE. They are approximate by design, since two people at the same "level" can differ a lot, but they give a reasonable estimate:

• Sedentary (× 1.2) — little or no exercise, mostly desk-bound.
• Lightly active (× 1.375) — light exercise or sport 1–3 days a week.
• Moderately active (× 1.55) — moderate exercise 3–5 days a week.
• Very active (× 1.725) — hard exercise or sport 6–7 days a week.
• Extra active (≈ × 1.9) — a very physical job plus hard daily training.

Most people land between sedentary and moderately active. When in doubt, it is usually safer to pick the lower level, then adjust after a few weeks based on how your weight actually responds.

Key terms

• BMR (Basal Metabolic Rate) — calories your body needs at complete rest to keep its basic functions going.
• TDEE (Total Daily Energy Expenditure) — BMR plus all your movement, activity and digestion over a full day.
• Mifflin-St Jeor equation — the modern formula this tool uses to estimate BMR from weight, height, age and sex.
• Activity factor — a multiplier (roughly 1.2 to 1.9) that scales BMR up to TDEE based on how active you are.
• Calorie (kcal) — a unit of food energy. The "calories" on food labels are really kilocalories, which is what this calculator reports.

Common misunderstandings

• "BMR is how much I should eat." It is not. BMR is a resting minimum; your eating target should be based on your TDEE and your goal.
• "The number is exact." Any formula gives an estimate. Real metabolism varies with genetics, muscle mass, hormones and health, so treat the result as a well-informed starting point.
• "A slow metabolism is why I can't lose weight." Large true differences in BMR between similar people are uncommon. Day-to-day calorie intake and activity usually matter far more.
• "More exercise always means a higher BMR." Exercise raises your TDEE for that day, but it only lifts your baseline BMR slowly, mainly by building muscle over time.

Frequently asked questions

What is BMR?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep you alive — powering your heart, brain and organs. It's the foundation of your total daily calorie needs, since everything you do adds on top of it.

How is BMR calculated?

This calculator uses the Mifflin-St Jeor equation, widely considered the most accurate for healthy adults. It combines your weight, height, age and sex to estimate your resting calorie burn per day. For men the formula adds 5 at the end, and for women it subtracts 161.

What's the difference between BMR and TDEE?

BMR is the calories you burn at rest; TDEE (Total Daily Energy Expenditure) is your BMR plus all activity and exercise. To turn your BMR into real daily calorie needs, use our calorie (TDEE) calculator.

Should I eat below my BMR to lose weight?

No. Your BMR is the minimum energy your body needs, so create your calorie deficit from your TDEE instead. A deficit of about 500 calories a day supports roughly 0.5 kg (1 lb) of loss per week while keeping you above BMR.

Why does BMR decrease with age?

BMR gradually declines with age, mainly because people lose muscle over time and muscle burns more calories at rest than fat. Staying active and doing strength training helps keep your BMR higher.

Is the Mifflin-St Jeor equation better than Harris-Benedict?

For most healthy adults, yes. Both formulas use the same inputs, but studies have found Mifflin-St Jeor predicts measured resting energy more closely, while the older Harris-Benedict equation tends to read slightly high. That is why this calculator uses Mifflin-St Jeor.

Which activity multiplier should I choose?

Match it to a typical week: sedentary (× 1.2) for little exercise, lightly active (× 1.375) for 1–3 days, moderately active (× 1.55) for 3–5 days, and very active (× 1.725) for 6–7 days. If you are unsure, pick the lower option and adjust after seeing how your weight responds.

Does BMR differ between men and women?

Yes. For the same height, weight and age, the equation gives men a higher BMR because they tend to carry more muscle, which burns more energy at rest. This is built into the formula through the +5 constant for men and the −161 constant for women.

This calculator provides estimates for general information only and is not medical advice. The Mifflin-St Jeor equation is not suitable for children or during pregnancy, and individual metabolism varies. Speak with a healthcare professional for personalized guidance. See our disclaimer.