Decoding Your Body’s Energy Engine
Calculate your Basal Metabolic Rate from your height, weight, age, and sex — and see exactly what it means for your daily calorie needs.
Enter your details, then tap Calculate.
| Activity level | Multiplier | Calories/day |
|---|---|---|
| Sedentary | ×1.2 | — |
| Light | ×1.375 | — |
| Moderate | ×1.55 | — |
| Very Active | ×1.725 | — |
| Extra Active | ×1.9 | — |
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body uses each day just to keep its core systems running — breathing, circulating blood, repairing cells — even if you stayed in bed all day. It is based on your height, weight, age, and sex, and is used as the starting point for almost every calorie or weight-loss calculation you’ll come across.
BMR is often confused with Total Daily Energy Expenditure (TDEE), but the two are not the same. TDEE consists of your BMR plus the calories burned through movement, exercise, and digesting food. On average, BMR accounts for 60–75% of total daily energy use, depending on how active you are. The formula below assumes a generally healthy resting adult — it isn’t valid during pregnancy, with an eating disorder, or alongside significant illness — and it shifts with muscle mass, genetics, and hormone levels such as thyroid function, which is why two people of the same height and weight can still land on different numbers.
The BMR formula
This calculator is based on the Mifflin-St Jeor equation — considered the more accurate formula for most adults, and the one that’s largely replaced the older Harris-Benedict method in clinical use:
Worked example
Take a 28-year-old man who weighs 80 kg and stands 178 cm tall:
- Weight 80 kg
- Height 178 cm
- Age 28
Activity levels & daily calories
BMR only counts calories spent at rest. To find your Total Daily Energy Expenditure (TDEE) — the number you should actually use to plan your calorie intake — multiply BMR by an activity factor. Using the example above (BMR = 1,777.50 Cal/day):
| Activity level | Multiplier | Calories/day |
|---|---|---|
| Sedentary | ×1.2 | 2,133.00 |
| Light | ×1.375 | 2,444.06 |
| Moderate | ×1.55 | 2,755.13 |
| Very Active | ×1.725 | 3,066.19 |
| Extra Active | ×1.9 | 3,377.25 |
How to use this calculator
- Pick your unit system — Metric (cm/kg) or Imperial (ft/in/lb).
- Enter your age, sex, height, and weight, then choose your activity level.
- Tap Calculate to see your BMR, your TDEE, and the full activity breakdown table.
- Use your TDEE — not your BMR alone — as the baseline for any calorie target. A deficit of roughly 300–500 Cal/day below TDEE is a common starting point for fat loss; how much you adjust depends on your goal.
- Recalculate every few weeks if your weight changes by more than a few kilograms — BMR moves with it.
Want your own number? Scroll up, enter your details, and hit Calculate.
Summary checklist
A quick recap of the worked example above.
- Multiply weight (kg) by 10
- Multiply height (cm) by 6.25
- Subtract 5 × age
- Add 5 for men, or subtract 161 for women
- Multiply by an activity factor to get TDEE
- A 28-year-old man at 80 kg and 178 cm has a BMR of 1,777.50 Cal/day — about 2,755 Cal/day at moderate activity.
Frequently asked questions
How accurate is a BMR calculator?
BMR calculators give a close estimate based on well-established formulas, but no online tool can be perfectly accurate. Actual metabolism is also affected by genetics, muscle mass, and hormone levels that a calculator can’t measure, so treat the result as a starting point rather than a fixed number.
Should I eat below my BMR to lose weight faster?
No. Eating below your BMR for an extended period isn’t recommended and can backfire. Aim for a moderate deficit below your TDEE instead — usually 300–500 Cal/day — rather than cutting under your BMR itself.
What’s the difference between BMR and TDEE?
BMR is the energy your body needs at complete rest. TDEE adds in everything else — walking, exercise, digestion — and is the number you should actually use to plan your calorie intake.
Can my BMR change over time?
Yes. BMR shifts with age, weight, and muscle mass, so recalculating it every few weeks during a weight-loss or muscle-building phase keeps your calorie targets accurate.
Why do two people with the same height and weight have different BMRs?
Muscle burns more calories at rest than fat does, so body composition — along with genetics and hormone levels such as thyroid function — can shift BMR even when height, weight, and age match.
Is Mifflin-St Jeor better than Harris-Benedict?
Most clinical sources now consider Mifflin-St Jeor more accurate for the general population. The Katch-McArdle formula can outperform both for people who know their body fat percentage, since it accounts for lean body mass directly.