BMR Calculator
Basal metabolic rate — calories at rest.
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Your basal metabolic rate is the number of calories your body burns just to keep you alive — breathing, circulating blood, maintaining temperature. This calculator estimates it with two trusted equations and shows what it means for your daily calorie needs.
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BMR — The Quick Answer
The Mifflin-St Jeor equation estimates BMR from your weight, height, age, and sex. For men: 10×weight + 6.25×height − 5×age + 5; for women, subtract 161 instead of adding 5.
Shortcut
Men: BMR = 10w + 6.25h − 5a + 5 | Women: 10w + 6.25h − 5a − 161
BMR as a share of total calories
| Component | Share of daily burn |
|---|---|
| Basal metabolic rate | 60–70% |
| Physical activity | 15–30% |
| Digesting food (thermic effect) | ~10% |
BMR is the biggest part of most people's daily calorie burn — typically 60–70%. That's why metabolism matters so much, and why muscle (which raises BMR) is valuable for weight management.
How It Works
The Formulas
Two established equations
Formula
Mifflin-St Jeor (men): 10w + 6.25h − 5a + 5 Mifflin-St Jeor (women): 10w + 6.25h − 5a − 161 Harris-Benedict (men): 88.362 + 13.397w + 4.799h − 5.677a
Variables
Weight (kg)
Body weight in kilograms — the largest driver of BMR.
Height (cm)
Height in centimetres.
Age (years)
BMR declines gradually with age as muscle mass tends to fall.
Note: Mifflin-St Jeor (1990) is generally considered more accurate for modern populations than the older Harris-Benedict equation, but both are estimates. Lab measurement (indirect calorimetry) is the gold standard.
Worked Example: BMR for a 30-Year-Old, 70 kg, 175 cm Man
Using the Mifflin-St Jeor equation
Multiply weight by 10
10 × 70 kg = 700
Add 6.25 × height in cm
6.25 × 175 = 1,093.75
Subtract 5 × age
5 × 30 = 150 (subtract)
Apply the sex constant (men +5)
700 + 1,093.75 − 150 + 5 = 1,649 kcal/day
Reference Guide
| Activity level | Multiplier | Approx. daily calories |
|---|---|---|
| BMR (complete rest) | — | 1,649 kcal |
| Sedentary (desk job) | × 1.2 | 1,979 kcal |
| Light (1–3 days/week) | × 1.375 | 2,267 kcal |
| Moderate (3–5 days/week) | × 1.55 | 2,556 kcal |
| Very active (6–7 days/week) | × 1.725 | 2,844 kcal |
What Your BMR Means for Your Diet
How to turn the number into a calorie target
BMR is roughly what you'd burn lying in bed all day. It's rarely wise to eat below it for long — your real daily needs are higher once any movement is added. Use it as the base you build on, not the number you aim to eat.
Best for: Understanding the minimum your body runs on
To find the calories you actually burn in a day, multiply BMR by an activity factor (about 1.2 if sedentary up to 1.9 if very active). That total is your TDEE — the figure you eat at to maintain weight, eat below to lose, or above to gain.
Best for: Setting a maintenance, loss, or gain calorie goal
The equation is a population estimate. Muscle mass raises BMR, and genetics, hormones (such as thyroid function), and age all shift it, so expect the figure to be within roughly 10% for most people. Track your weight over 2–3 weeks and adjust rather than trusting the estimate to the calorie.
Best for: Treating the result as a starting estimate to calibrate
What Is Basal Metabolic Rate (BMR)?
Your basal metabolic rate is the number of calories your body burns at complete rest just to keep you alive — powering your heart, brain, breathing, and the constant work of maintaining your cells and temperature. For most people it accounts for 60–70% of total daily calorie burn, far more than exercise, which is why it sits at the centre of any calorie plan. This calculator estimates BMR with the Mifflin-St Jeor equation (widely regarded as the most accurate general formula) and shows the Harris-Benedict figure for comparison. Multiply BMR by an activity factor and you get your TDEE — the calories you actually use in a day.
Key Features
💡 Pro Tips
- →Don't crash-diet below your BMR for extended periods — very low intake can prompt the body to adapt and lower metabolic rate, making progress harder.
- →Building muscle is the most reliable way to nudge your BMR up over time, since muscle tissue burns more calories at rest than fat.
- →Use the moderate activity multiplier as a realistic default — most people overestimate how active they are, which inflates their calorie target.
- →Re-run the numbers after a significant weight change; your BMR falls as you lose weight because there's less body mass to maintain.
Common Mistakes
Eating at your BMR to lose weight
BMR is calories at rest, not your daily need. Eating at BMR while being active creates an unintentionally large deficit that's hard to sustain and can cost muscle. Base your target on TDEE (BMR × activity), not BMR alone.
Confusing BMR with TDEE
BMR is the resting floor; TDEE adds the calories you burn moving and digesting. TDEE is always higher, and it's the number that matters for maintaining, losing, or gaining weight.
Expecting the estimate to be exact
The equation is based on population averages and ignores body composition. Two people with the same height, weight, age, and sex can have different real BMRs depending on muscle mass and genetics. Treat it as a well-informed starting point.
Blaming a 'slow metabolism' for stalled progress
Large differences in BMR between similar people are uncommon. Most apparent variation comes from non-exercise movement (NEAT) and from under-reporting food intake, not a broken metabolism.
Research & Citations
Sources and standards referenced for the factual claims on this page
- [1]
Mifflin, M. D., St Jeor, S. T., et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2).
The Mifflin-St Jeor equation used as this calculator's primary method.
View source - [2]
Roza, A. M. & Shizgal, H. M. (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition, 40(1).
The revised Harris-Benedict equation shown for comparison.
View source - [3]
Academy of Nutrition and Dietetics (2023). Energy requirements and estimating resting metabolic rate. eatright.org.
General guidance on resting metabolism and daily energy needs.
View source
This calculator is a reference tool, not a substitute for professional advice. Verify important health, financial, legal, or safety decisions with a suitably qualified professional.
Last updated: October 8, 2026
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Frequently Asked Questions
What is BMR?
Basal metabolic rate is the number of calories your body uses at complete rest to maintain basic functions like breathing, circulation, and temperature. It's the floor of your daily energy needs, before any activity.
What's the difference between BMR and TDEE?
BMR is calories burned at rest; TDEE (total daily energy expenditure) is BMR plus the calories you burn through activity and digestion. TDEE is always higher — you get it by multiplying BMR by an activity factor.
How can I increase my BMR?
Building muscle is the most reliable way, since muscle tissue burns more calories at rest than fat. Staying active, eating enough protein, and avoiding very low-calorie crash diets (which can suppress BMR) also help.
Which BMR formula is most accurate?
Mifflin-St Jeor is widely regarded as the most accurate general equation for healthy adults, which is why it's the primary result here. Harris-Benedict is shown for comparison. Neither accounts for body composition, so very muscular or lean people may differ.