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BMR calculator: your resting calorie burn
Find out how many calories your body burns at complete rest using the Mifflin-St Jeor equation — the foundation for every other calorie calculation on this site.
BMR calculator
Your result
This is roughly how much energy your body uses in 24 hours just to keep your organs, brain and nervous system running — before you've taken a single step. To estimate your total daily calorie need including activity, use the TDEE calculator next.
About this tool
What BMR measures and who it's for
Your Basal Metabolic Rate is the calorie cost of simply being alive — it's the largest single piece of your total daily energy use for most people, typically 60–70% of it.
Use this calculator if you want to understand your own metabolism, or if you're building a calorie target from first principles rather than relying on a generic number. For a full daily total that includes activity, continue to the TDEE calculator.
Step by step
How to use the BMR calculator
- 1
Choose your units
Switch between Metric and Imperial at the top of the calculator card.
- 2
Enter sex, age, height and weight
All four are required — the Mifflin-St Jeor equation uses each one.
- 3
Select Calculate BMR
Your resting calorie number appears immediately below the form.
- 4
Use it as a building block
Take this number to the TDEE calculator to add your activity level.
Methodology
The Mifflin-St Jeor formula
Men
10W + 6.25H − 5A + 5
Women
10W + 6.25H − 5A − 161
Where W is weight in kilograms, H is height in centimetres, and A is age in years. Imperial entries are converted to metric internally before the formula runs, so results are identical either way.
Worked example
Example calculation
A 30-year-old woman, 165 cm, 65 kg: (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1,031.25 − 150 − 161 = ≈ 1,370 calories/day at complete rest.
Watch out for
Common mistakes
- Eating at BMR level. BMR excludes all movement — eating exactly this many calories long-term is an extreme deficit for almost everyone.
- Mixing unit systems. Entering height in inches but weight in kilograms will give a meaningless result — use the unit toggle to keep both consistent.
- Expecting daily precision. BMR is a population-derived estimate; real metabolism varies by roughly ±10% between individuals of the same stats.
Be aware
Assumptions and limitations
- Mifflin-St Jeor was derived from a general adult population and doesn't account for individual muscle mass directly.
- Not validated for pregnancy, certain medical conditions, or extreme body compositions (very low or very high body fat).
- Built for adults and older teenagers aged 15 and over.
- Results are estimates for general information, not a clinical metabolic test.
Questions
Frequently asked questions
What is BMR?
Basal Metabolic Rate is the number of calories your body needs in 24 hours to keep its core functions running — breathing, circulation, cell repair, brain activity — assuming you stayed in bed all day and did nothing else.
Which formula does this calculator use?
The Mifflin-St Jeor equation, published in 1990. It's widely regarded in dietetics as more accurate for the general population than the older Harris-Benedict equation, which tends to overestimate calorie needs.
Why does the formula ask for sex?
Mifflin-St Jeor uses a sex-specific constant because, on average, men carry more lean muscle mass than women at the same height and weight, and muscle burns more energy than fat tissue at rest. It's a population-level adjustment, not a precise measurement of your individual body composition.
Is BMR the same as the calories I should eat?
No. BMR only covers resting function — it doesn't include the calories you burn moving around or exercising. For a full daily calorie estimate, use the TDEE calculator, which multiplies BMR by an activity factor.
What is a normal BMR for a woman?
For an adult woman aged 25–40, a typical BMR falls between 1,300 and 1,600 kcal/day, depending on height and weight. Taller and heavier women have higher BMRs; shorter and lighter women sit at the lower end. The Mifflin-St Jeor equation your result is based on accounts for these differences automatically.
What is a normal BMR for a man?
For an adult man aged 25–40, a typical BMR falls between 1,600 and 2,000 kcal/day. Men generally have higher BMRs than women of the same age, height and weight because they carry proportionally more lean muscle mass, which is metabolically more active than fat tissue.
How can I increase my BMR?
Building muscle through resistance training is the most effective long-term strategy — muscle tissue burns more calories at rest than fat tissue. Staying well-hydrated, eating adequate protein (which has a higher thermic effect than fat or carbs), and avoiding very low-calorie diets (which suppress metabolic rate) also help maintain a healthy BMR.
Does BMR slow down with age?
Yes. BMR typically declines by around 1–2% per decade from your mid-20s onward, largely because muscle mass decreases with age unless actively maintained through resistance training. The Mifflin-St Jeor formula includes age as a variable precisely because of this relationship — older adults will see a lower BMR estimate than younger adults of the same height and weight.
Estimates, not medical advice
FitnessCalculator.info provides general health information for educational purposes only and does not replace advice from a qualified doctor or registered dietitian.