01What BMR means
Your Basal Metabolic Rate (BMR) is the amount of energy your body uses to perform basic functions at rest. This includes functions such as breathing, circulation and cell repair and it accounts for the largest portion of your total daily energy expenditure. For this reason BMR is frequently used as the starting point for many diet and energy plans.
BMR (Basal Metabolic Rate) is the minimum energy your body requires for survival whilst at rest. The Overview tab details how the BMR Calculator works and how your activity level can multiply up your BMR to provide you with your total daily energy requirements, plus gives you some real ways that you can put it to use. The Formula tab fully outlines the calculations to arrive at your BMR, and provides an example calculation to illustrate how the numbers are used.
02What this calculator does
The BMR Calculator uses your age, sex, height and weight in either metric or US units to estimate your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, the most commonly used BMR formula found in clinical practice today. It is also the most commonly used BMR formula in BMR calculators found on the web.
The BMR calculation is then multiplied by your activity factor for the level of exercise you perform in order to work out your Total Daily Energy Expenditure (TDEE), ie the number of calories that you actually use on a daily basis. The input data for your calculation has been validated so that the calculation will only work with relevant numbers – no blank fields, no zero or negative numbers for weight etc, and no age outside of human lifetime parameters.
03Activity levels & daily calories
A BMR calculation gives you the number of calories that you will burn sitting still at rest. Then you would use that number times your activity factor for the week in order to calculate your daily calories needed for how much you should eat.
TDEE (not BMR) for setting up a calorie requirement for weight loss or muscle gain: for weight loss aim for a 300-500 calorie “deficit” below TDEE and for muscle gain aim for a small “surplus” above TDEE.
A BMR calculator gives a solid estimate, but it is a population-based formula, not a personal measurement. A few things shift the real number:
- Muscle vs fat. Muscle burns more energy at rest than fat, so two people of the same age, height, and weight can have different BMRs depending on body composition.
- Age. BMR tends to fall as you get older, partly because muscle mass declines — so it is worth recalculating every few years.
- Hormones and health. Thyroid levels, genetics, illness, and some medications all nudge BMR up or down.
- Pregnancy and children. The standard adult equation is not designed for pregnancy or for under-18s, whose needs differ.
- Out-of-range inputs are rejected. Age must be 15–80 and height and weight within sensible limits; the calculator flags anything outside them instead of returning a misleading figure.
- Pick Metric (cm, kg) or Imperial (ft/in, lb), then choose your sex.
- Enter your age, height, and weight.
- Tap Calculate to see your BMR and a table of daily calories (TDEE) for five activity levels.
Tips for using your result
- Use your TDEE, not your BMR alone, as the baseline for any calorie target — BMR is just the resting portion.
- For fat loss, a deficit of roughly 300–500 calories below TDEE is a common, sustainable starting point.
- Recalculate every few weeks if your weight changes by more than a couple of kilograms, since BMR moves with it.
01The BMR formula
This calculator uses the Mifflin-St Jeor equation (the most frequently used equation in clinical settings and more accurate than the Harris-Benedict equation for example) for calculation of basal metabolic rate. It uses the same formula for all and then makes a small correction for sex.
Where:
- weight = your body weight in kilograms (the calculator converts pounds for you)
- height = your standing height in centimetres
- age = your age in years
- +5 / −161 = the sex constant: +5 for men, −161 for women
The only difference between the two is the constant at the end (+5 for men, −161 for women), which reflects average differences in body composition. The result is your BMR in calories per day.
02Worked example
Take a 28-year-old man who weighs 80 kg and stands 178 cm tall. Substitute into the men’s formula one step at a time:
One typically uses TDEE rather than just BMR to calculate a daily calorie requirement. As an example, at a sedentary level (×1.2) that works out to approximately 2,133 calories per day, while at a moderate level (×1.55) it is approximately 2,755 calories per day.
BMR Calculator
| Activity level | × | Cal/day |
|---|---|---|
| Sedentary little/no exercise | 1.2 | — |
| Light 1–3 days/week | 1.375 | — |
| Moderate 3–5 days/week | 1.55 | — |
| Very active 6–7 days/week | 1.725 | — |
| Extra active hard job / 2× training | 1.9 | — |