BMR Calculator: Calculate Your Basal Metabolic Rate
Find out how many calories your body burns at rest using our BMR Calculator. This value helps you understand your metabolism and can be used to plan your diet and exercise routines.
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What Is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to stay alive — powering breathing, circulation, cell repair, hormone regulation, and brain activity. It represents roughly 60–70% of your total daily calorie burn for most adults, making it the single largest component of your energy expenditure.
Knowing your BMR is the foundation for any calorie-based weight plan. It tells you the minimum number of calories you'd need if you stayed in bed all day. From there, activity multipliers estimate your Total Daily Energy Expenditure (TDEE).
BMR vs. RMR: What's the Difference?
The terms are often used interchangeably, but they aren't identical:
- BMR is measured under strict lab conditions — after an overnight fast, in a thermally neutral room, lying still, fully awake. It's the "gold standard" but impractical to measure casually.
- RMR (Resting Metabolic Rate) is measured under less strict conditions — at rest, but not necessarily fasted or in a controlled environment. It typically runs 3–5% higher than BMR.
Both prediction equations on this page actually estimate RMR, but they're commonly called "BMR calculators" because that's how most people search. For practical purposes, treat them as equivalent.
How BMR Is Calculated
Because measuring BMR directly requires a metabolic cart, most applications use prediction equations. Three are widely used:
1. Mifflin-St Jeor (Recommended)
Published in 1990 and endorsed by the Academy of Nutrition and Dietetics as the most accurate equation for the general population.
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
2. Harris-Benedict (Revised 1984)
The classic equation. It overestimates by about 5% on average compared to modern methods, but is still widely cited.
- Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
- Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
3. Katch-McArdle (Best If You Know Body Fat %)
Uses lean body mass rather than total weight, making it more accurate for lean, muscular, or obese individuals.
- BMR = 370 + (21.6 × lean body mass in kg)
- Lean mass = weight × (1 − body fat % ÷ 100)
Which Equation Should You Use?
| Situation | Best Equation |
|---|---|
| General population | Mifflin-St Jeor |
| Muscular / athletic | Katch-McArdle (if you know body fat %) |
| Obese (BMI ≥ 30) | Mifflin-St Jeor (tends to be most accurate) |
| Comparing to older studies | Harris-Benedict |
| Pregnancy / lactation | Add 300–500 kcal to Mifflin-St Jeor result |
| Children / adolescents | Schofield or FAO/WHO equations (age-specific) |
Example (Mifflin-St Jeor)
35-year-old male, 80 kg, 180 cm:
- 10 × 80 = 800
- 6.25 × 180 = 1,125
- 5 × 35 = 175
- 800 + 1,125 − 175 + 5 = 1,755 kcal/day BMR
From BMR to TDEE: Activity Multipliers
Your BMR is what you'd burn in bed. To get your total daily burn, multiply by an activity factor:
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | BMR × 1.2 |
| Lightly active | Light exercise 1–3 days/week | BMR × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | BMR × 1.55 |
| Very active | Hard exercise 6–7 days/week | BMR × 1.725 |
| Extremely active | Physical job + hard training twice a day | BMR × 1.9 |
Example: A BMR of 1,755 kcal with a moderately active lifestyle → 1,755 × 1.55 ≈ 2,720 kcal/day TDEE.
For a full TDEE calculation with body fat–based options, use our TDEE Calculator.
Factors That Affect Your BMR
| Factor | Effect on BMR |
|---|---|
| Lean body mass (muscle) | Strongest controllable factor; more muscle = higher BMR |
| Age | Decreases ~1–2% per decade after 20, mostly from muscle loss |
| Sex | Men average 5–10% higher, largely due to more lean mass |
| Body size | Larger bodies burn more at rest |
| Body fat % | Fat tissue is metabolically less active than muscle |
| Thyroid function | Hypothyroidism lowers BMR by 10–20%; hyperthyroidism raises it |
| Genetics | Individual variation of ±5–10% at the same body composition |
| Climate | Cold exposure and heat both raise BMR slightly |
| Medications | Beta blockers, some antidepressants, and corticosteroids can shift it |
| Pregnancy / lactation | Adds ~300 kcal/day (pregnancy) and ~500 kcal/day (lactation) |
How to Use BMR for Weight Management
BMR tells you the floor. TDEE tells you the target. The difference between them is the fat-loss or muscle-gain zone.
To Maintain Weight
Eat at your TDEE. Weight stays stable.
To Lose Weight
- Estimate TDEE using BMR × activity multiplier.
- Subtract 300–500 kcal/day for a moderate deficit (about 0.5–1 lb loss/week).
- Never eat below your BMR for extended periods — this accelerates muscle loss and metabolic adaptation.
- Set protein high (1.6–2.2 g/kg) to preserve muscle — see our Protein Calculator.
- Resistance train 3–4× per week.
Use our Calorie Deficit Calculator to plan the deficit and the Weight Loss Calculator to project a timeline.
To Gain Weight (or Muscle)
- Add 250–500 kcal/day above TDEE.
- Target 0.25–0.5% body weight gain per week to minimize fat gain.
- Keep protein at 1.6–2.2 g/kg and train with progressive overload.
How to Increase Your BMR
You can't change age or genetics, but you can move the needle on the biggest controllable factor — muscle mass:
- Resistance train 3–4× per week. Adding 5 kg of lean mass can raise BMR by roughly 50–100 kcal/day.
- Eat enough protein. Protein has a higher thermic effect (~20–30% of calories burned during digestion) than carbs or fat.
- Don't crash diet. Severe deficits cause "metabolic adaptation" — BMR can drop 10–15% and stay lower for months.
- Sleep 7–9 hours. Chronic sleep deprivation lowers BMR and increases hunger hormones.
- Move more in daily life. Non-exercise activity (walking, standing, fidgeting) can vary by 300–800 kcal/day between people.
- Manage stress. Chronic cortisol elevation is associated with lower lean mass and higher fat storage.
Limitations of BMR Calculators
- They're estimates. Individual accuracy is typically ±10% — a 1,700 kcal estimate might be anywhere from 1,530 to 1,870.
- Activity multipliers are rough. "Moderately active" means different things to different people.
- They miss metabolic adaptation. After prolonged dieting, actual BMR can run below predictions.
- Not ideal for medical use. Clinical nutrition (ICU, eating disorders, bariatric surgery) uses indirect calorimetry or disease-specific equations.
- Not validated for children. Use Schofield or WHO equations for those under 18.
Use BMR as a starting point, then adjust based on real-world results over 2–4 weeks.
Frequently Asked Questions About BMR
What is a normal BMR?
For most adults, BMR falls between 1,200 and 2,000 kcal/day. A 30-year-old woman of average build is typically 1,300–1,500; a 30-year-old man 1,600–1,800. Larger, younger, or more muscular people sit higher.
What's the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE includes BMR plus all activity — walking, exercise, digesting food, fidgeting. TDEE is always higher than BMR (usually 1.2–1.9× BMR). Use our TDEE Calculator for the full number.
Which BMR formula is most accurate?
Mifflin-St Jeor is the most accurate for the general population, per the Academy of Nutrition and Dietetics. Katch-McArdle is best if you know your body fat percentage. Harris-Benedict overestimates by ~5%.
Can I increase my BMR?
Yes, mainly by building muscle. Adding 5 kg of lean mass can raise BMR by 50–100 kcal/day. Protein intake, sleep, and avoiding prolonged crash diets also help preserve BMR.
Should I eat my BMR calories to lose weight?
Usually not. BMR is the floor, not the target. For healthy weight loss, eat at TDEE minus 300–500 kcal — which is typically above BMR. Eating below BMR for long periods risks muscle loss and metabolic slowdown.
Why does BMR decrease with age?
Mostly because lean muscle mass declines with age — about 3–8% per decade after 30 if you don't resistance train. The BMR equation captures the average trend, but training can slow or reverse it.
Does BMR differ between men and women?
Yes — men average 5–10% higher BMR than women of the same weight and age, largely due to higher lean mass. That's why the equations have separate constants.
Does pregnancy change BMR?
Yes. BMR rises modestly through pregnancy and substantially during lactation — typically +300 kcal/day in late pregnancy and +400–500 kcal/day while nursing. Use the pregnancy-adjusted guidance from your doctor.
How accurate is the BMR calculator?
Typically within ±10% of measured BMR. Accuracy is highest for average-build adults and lowest for very muscular, very lean, or very obese individuals — where Katch-McArdle is preferable.
Do I need to recalculate BMR?
Yes, after significant weight change (±5 kg), age changes, pregnancy, or after building meaningful muscle. Recheck every 3–6 months during active weight management.
Can I lose weight eating only my BMR?
Technically yes, if your BMR is below your TDEE. But eating only BMR ignores the activity you do and risks under-fueling recovery. Use TDEE as your baseline and apply a moderate deficit.
Does intermittent fasting change BMR?
Not directly. Short fasts (16–24 hours) have minimal effect on BMR. Prolonged multi-day fasting does lower BMR. What matters more is total calorie intake and protein.
Related Metabolism and Weight Tools
- TDEE Calculator — total daily energy expenditure
- Maintenance Calorie Calculator — maintain weight
- Calorie Deficit Calculator — plan a deficit
- Weight Loss Calculator — timeline to goal
- Macro Calculator for Weight Loss — macros for fat loss
- Protein Calculator — daily protein targets
- BMI Calculator — body mass index
- Body Fat Percentage Calculator — fat vs. lean mass
- Daily Calorie Calculator — all-in-one calorie estimate
When to Consult a Professional
This BMR Calculator provides an educational estimate based on validated prediction equations. It does not diagnose metabolic conditions and it is not a clinical assessment. Consult a physician or registered dietitian if you have a thyroid disorder, diabetes, kidney or liver disease, an eating disorder, or a chronic illness; if you're pregnant or breastfeeding; or if you're planning a significant weight-loss or weight-gain program. For clinical settings — including ICU, bariatric surgery, and eating disorder treatment — indirect calorimetry or disease-specific equations should be used instead of these estimates.