Written by Tou Calo Nutrition Team · Vulcan Labs · Updated July 2026. General health information only — not personalised medical advice.
Learning how to calculate BMR takes under 60 seconds with the right formula. BMR — Basal Metabolic Rate — is the number of calories your body burns at complete rest just to keep you alive. It is the single most important number in any nutrition plan, because every calorie target — whether for weight loss, maintenance or muscle gain — is built on top of it. This guide shows you the exact formula, walks through worked examples for both men and women, and explains how to turn your BMR into a real daily calorie target you can actually use.
Skip the maths: Use our free BMR calculator to get your result instantly — no formula required. Then come back here to understand exactly what the number means and how to use it.
In this guide
- What is BMR?
- The BMR formula — Mifflin-St Jeor
- Worked examples — men and women
- How to go from BMR to a real daily calorie target
- What affects your BMR
- FAQ
What is BMR?
BMR stands for Basal Metabolic Rate — the number of calories your body burns at complete rest over 24 hours to keep you alive. This includes energy for breathing, circulating blood, regulating body temperature, keeping organs functioning and maintaining brain activity. It does not include any calories burned through movement, exercise or digesting food.
BMR accounts for approximately 60–75% of your total daily calorie burn — making it by far the largest component of your energy expenditure. Even on a completely sedentary day, the majority of calories you burn come from resting metabolism, not activity.
Two important things BMR is not:
- BMR is not your daily calorie target — it is only your resting baseline. Eating at your BMR level is too low for most active adults and can cause muscle loss and metabolic adaptation.
- BMR is not fixed forever — it changes with age, muscle mass, body weight and hormonal status. Recalculate it whenever your body composition or weight changes significantly.
How to calculate BMR — the Mifflin-St Jeor formula
The most accurate way to calculate BMR without lab equipment is the Mifflin-St Jeor equation, published in 1990 and validated as the most accurate non-lab formula for most adults. It uses four variables: weight, height, age and sex.
Mifflin-St Jeor formula
| Sex | Formula |
|---|---|
| Male | BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 |
| Female | BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161 |
The only difference between the male and female formulas is the final constant: +5 for males, −161 for females. This reflects the average difference in lean muscle mass between the sexes, which drives resting calorie burn.
Units required
- Weight: kilograms (kg) — divide pounds by 2.205 to convert
- Height: centimetres (cm) — multiply inches by 2.54 to convert
- Age: years
If you prefer not to calculate manually, our free BMR calculator applies the Mifflin-St Jeor formula automatically — enter your details and get your result in seconds, in both metric and imperial units.
Worked examples — how to calculate BMR step by step
Example 1 — Male, 35 years old, 80 kg, 178 cm
Applying the male Mifflin-St Jeor formula:
| Step | Calculation | Result |
|---|---|---|
| 10 × weight | 10 × 80 kg | 800 |
| 6.25 × height | 6.25 × 178 cm | 1,112.5 |
| 5 × age | 5 × 35 | 175 |
| Male constant | + 5 | 5 |
| BMR = 800 + 1,112.5 − 175 + 5 | Total | 1,742 kcal/day |
Example 2 — Female, 28 years old, 62 kg, 165 cm
| Step | Calculation | Result |
|---|---|---|
| 10 × weight | 10 × 62 kg | 620 |
| 6.25 × height | 6.25 × 165 cm | 1,031.25 |
| 5 × age | 5 × 28 | 140 |
| Female constant | − 161 | −161 |
| BMR = 620 + 1,031.25 − 140 − 161 | Total | 1,350 kcal/day |
Skip the manual calculation
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Calculate My BMR →How to go from BMR to a real daily calorie target
Once you know how to calculate BMR, the next step is converting it into a number you can actually eat to. BMR alone is not a calorie target — it is only your resting baseline. To find how many calories you need per day, you multiply your BMR by an activity factor to get your TDEE (Total Daily Energy Expenditure).
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little to no exercise | × 1.2 |
| Lightly active | Light exercise 1–3 days/week | × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | × 1.55 |
| Very active | Hard exercise 6–7 days/week | × 1.725 |
| Extremely active | Physical job + hard daily training | × 1.9 |
Worked example continued: The 35-year-old male from Example 1 has a BMR of 1,742 kcal. If he exercises moderately 3–5 days per week:
TDEE = 1,742 × 1.55 = 2,700 kcal/day (maintenance)
From this TDEE, setting a goal is straightforward:
- Weight loss: TDEE minus 300–500 kcal/day → 2,200–2,400 kcal/day
- Maintenance: Eat at TDEE → 2,700 kcal/day
- Weight gain: TDEE plus 300–500 kcal/day → 3,000–3,200 kcal/day
Use our free TDEE calculator to apply this automatically, or our calorie deficit calculator to set your exact fat loss target.
What affects your BMR
Understanding how to calculate BMR is more useful when you also understand what drives it — because the same formula will give different results for people with the same height and weight if their body composition differs.
- Muscle mass — the biggest controllable factor: Muscle tissue burns approximately 6–10 calories per kg at rest, compared to 2–3 kcal/kg for fat tissue. Two people with the same body weight but different muscle-to-fat ratios can have BMRs that differ by 200–300 kcal/day. This is why resistance training raises BMR over time.
- Age: BMR declines by approximately 1–2% per decade after age 30, primarily because lean muscle mass decreases with age. This is the main reason calorie needs change over time even without changes in activity.
- Body weight: Heavier bodies have more metabolically active tissue and therefore higher BMRs. When you lose weight, your BMR decreases — which is why recalculating every 5–10 kg of weight change matters.
- Sex: Males typically have higher BMRs than females of the same height, weight and age — largely because of higher average lean muscle mass. This is reflected directly in the Mifflin-St Jeor formula.
- Hormones: Thyroid hormones are the primary metabolic regulators — hyperthyroidism raises BMR, hypothyroidism lowers it. This is why standard BMR formulas can underestimate or overestimate for people with thyroid conditions.
How to calculate BMR — FAQ
What is the most accurate formula for calculating BMR?
The Mifflin-St Jeor equation (1990) is considered the most accurate BMR formula for the general adult population — validated to within ±10% for most non-athletic adults. It is more accurate than the older Harris-Benedict equation, which tends to overestimate by about 5%. The Katch-McArdle formula is more accurate for lean athletes who know their body fat percentage, as it accounts for lean mass directly. Use our free BMR calculator to apply Mifflin-St Jeor automatically.
Should I eat at my BMR?
No — eating at your BMR is not safe or appropriate for most active adults. BMR is your resting-only calorie burn. Even a sedentary person burns additional calories through movement, digestion and daily activity. Eating only at BMR level over time causes muscle loss and metabolic adaptation. Always calculate TDEE (BMR × activity multiplier) first, then set your calorie target relative to TDEE. Our calorie deficit calculator handles this automatically.
How often should I recalculate my BMR?
Recalculate your BMR whenever your weight changes by 5 kg or more, when you significantly change your exercise habits, or if you are not seeing expected results from your current calorie target. BMR decreases as you lose weight — if you set a deficit based on your starting BMR and never recalculate, the deficit shrinks over time and weight loss slows.
What is the difference between BMR and TDEE?
BMR is the calories your body burns at complete rest — no movement, no digestion. TDEE (Total Daily Energy Expenditure) is your total calorie burn across a full day, including BMR plus all movement and food digestion. TDEE is always higher than BMR. For most adults, TDEE is 1.2–1.9× their BMR depending on activity level. Your daily calorie target should be based on TDEE, not BMR alone. Use our TDEE calculator to find your full daily burn.
How accurate is BMR calculation?
The Mifflin-St Jeor equation is accurate to within ±10% for most healthy adults — meaning a calculated BMR of 1,600 kcal could reflect a true BMR of 1,440–1,760 kcal. Accuracy is lower for very lean athletes, people with thyroid conditions, and older adults with low muscle mass. The most accurate way to measure BMR is indirect calorimetry in a clinical setting — but for practical nutrition planning, the formula provides a reliable enough starting point. Track your actual weight response over 2–4 weeks and adjust your calorie target accordingly.
Disclaimer: BMR calculations are estimates based on population averages and may not reflect individual metabolic variation. Consult a registered dietitian or healthcare provider for personalised dietary guidance.
Written by Tou Calo Nutrition Team — Vulcan Labs
The team behind Tou Calo AI Calorie Counter.
Related tools:
BMR Calculator — calculate your result instantly
TDEE Calculator — total daily calorie burn
Calorie Deficit Calculator — your fat loss target
calories and macros in 3 seconds.