BMR Calculator (Basal Metabolic Rate)

This BMR calculator works out your basal metabolic rate — the calories your body burns at complete rest — from two trusted equations. Your basal metabolic rate is the calories your body burns if you did nothing all day but breathe. It is the largest part of your daily energy use and the foundation every diet plan is built on. Enter your age, sex, height and weight and this calculator returns your BMR from the two most-used equations.

The equations

Mifflin-St Jeor (men):   10·kg + 6.25·cm − 5·age + 5
Mifflin-St Jeor (women): 10·kg + 6.25·cm − 5·age − 161

The revised Harris-Benedict equation is shown alongside it. Both estimate resting energy from the same four inputs; Mifflin-St Jeor is generally preferred today.

From BMR to daily calories

BMR alone is not what you eat to maintain weight. Multiply it by an activity factor — about 1.2 for sedentary up to 1.9 for very active — to get your TDEE. The TDEE calculator does that step and adds cut and bulk targets.

Worked example

A 30-year-old man, 180 cm, 80 kg:

Mifflin-St Jeor:  10×80 + 6.25×180 − 5×30 + 5 = 800 + 1,125 − 150 + 5 = 1,780 kcal
Harris-Benedict:  88.362 + 13.397×80 + 4.799×180 − 5.677×30 ≈ 1,854 kcal

The two published equations disagree by 74 kcal, about 4%. That gap is not a bug in either formula — it is the honest size of the uncertainty, and it is why a BMR should be read as a starting point to adjust rather than a measurement of your body. For a 30-year-old woman at 165 cm and 65 kg the same comparison gives roughly 1,370 against 1,430.

What BMR is not

It is not the number of calories you burn in a day, and treating it as one is the most common mistake made with it. BMR covers only the energy spent keeping you alive at complete rest: circulation, breathing, cell turnover, brain function, temperature regulation. It excludes standing up, walking to the kettle, digesting food and every minute of exercise.

It is not a fixed property either. It falls with age, drops when you lose weight (partly because there is less tissue to maintain, partly through metabolic adaptation), rises with muscle mass, and shifts with thyroid function and pregnancy. A figure computed today describes today.

The thermic effect of food sits outside it as well and accounts for roughly a tenth of what you eat — slightly more on a high-protein diet, because protein costs more to process than fat or carbohydrate.

Entering your numbers

• Sex — the equations differ by a constant, +5 for men and −161 for women, reflecting average differences in lean mass rather than anything about an individual.
• Weight and height — metric or imperial, converted internally to kilograms and centimetres before the formula runs.
• Age — in years. Mifflin-St Jeor subtracts 5 kcal for each year.

Weigh yourself in the morning before eating, in similar clothing, and use an average of several days rather than a single reading; daily swings of a kilogram from water and food residue are entirely normal. Measure height without shoes. TDEE Calculator takes this figure and applies the activity multiplier that turns it into something you can actually eat to.

Private and precise

This calculator produces estimates from published formulas and is not medical advice. For anything about your health, talk to a doctor or a registered dietitian.