BMR Calculator (2026)
Your body burns calories every second just staying alive - breathing, pumping blood, repairing cells - before you've taken a single step. That number is your Basal Metabolic Rate, and it's the foundation every calorie or diet plan should be built on. Use this BMR calculator to find your resting calorie burn with the Mifflin-St Jeor equation, then see your full daily calorie needs (TDEE) based on how active you actually are.
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What BMR Measures
Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest, in a fasted state, in a neutral temperature environment, just to keep essential functions running - breathing, circulating blood, regulating body temperature, and repairing and replacing cells. It represents the largest share of most people's daily calorie burn, typically 60% to 75% of total calories burned in a day, even before any deliberate movement or exercise is added.
- BMR typically accounts for 60% to 75% of total daily calories burned
- Calculated from age, sex, height, and weight using the Mifflin-St Jeor equation
- Typical adult BMR ranges from roughly 1,300 to 1,800 calories per day
- More muscle mass raises BMR since muscle burns more calories at rest than fat
- TDEE = BMR × activity multiplier gives your full daily calorie needs
- Eating below BMR is not recommended, even for weight loss goals
The Mifflin-St Jeor Formula
Published in 1990 and now the most widely recommended BMR equation for the general adult population, endorsed by the Academy of Nutrition and Dietetics over older alternatives:
Men: BMR = 10 × Weight(kg) + 6.25 × Height(cm) − 5 × Age(years) + 5
Women: BMR = 10 × Weight(kg) + 6.25 × Height(cm) − 5 × Age(years) − 161
The formula only differs by the final constant (+5 for men, −161 for women), which reflects the average difference in lean body mass and metabolic rate between the sexes measured across large validation studies.
Other BMR Formulas
| Formula | Year | Notes |
|---|---|---|
| Mifflin-St Jeor | 1990 | Most accurate for the general population; used by this calculator |
| Revised Harris-Benedict | 1984 | Older, widely used equation; tends to slightly overestimate BMR compared to Mifflin-St Jeor |
| Original Harris-Benedict | 1919 | Historic formula, based on a smaller and less diverse study population |
| Katch-McArdle | 1996 | Uses lean body mass instead of total weight; more accurate for those who know their body fat % |
Katch-McArdle can be more precise for very lean or very muscular individuals since it's based on lean mass rather than total weight, but it requires an accurate body fat percentage measurement, which most people don't have readily available - making Mifflin-St Jeor the more practical default for most calculators.
From BMR to TDEE: Activity Multipliers
BMR alone only tells you what your body burns doing nothing. Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor to estimate your true daily calorie need, including movement, exercise, and the calories used digesting food:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little to no exercise, desk job |
| Lightly Active | 1.375 | Light exercise 1-3 days per week |
| Moderately Active | 1.55 | Moderate exercise 3-5 days per week |
| Very Active | 1.725 | Hard exercise 6-7 days per week |
| Extremely Active | 1.9 | Physical job plus daily intense training |
Worked Examples
A 30-year-old man, 175 cm tall, weighing 80 kg. BMR = 10×80 + 6.25×175 − 5×30 + 5 = 800 + 1,093.75 − 150 + 5 = 1,749 calories/day. With a moderately active multiplier (1.55): TDEE = 1,749 × 1.55 ≈ 2,711 calories/day.
A 28-year-old woman, 165 cm tall, weighing 62 kg. BMR = 10×62 + 6.25×165 − 5×28 − 161 = 620 + 1,031.25 − 140 − 161 = 1,350 calories/day. With a lightly active multiplier (1.375): TDEE = 1,350 × 1.375 ≈ 1,856 calories/day.
A 55-year-old man, 178 cm tall, weighing 90 kg. BMR = 10×90 + 6.25×178 − 5×55 + 5 = 900 + 1,112.5 − 275 + 5 = 1,743 calories/day. With a sedentary multiplier (1.2): TDEE = 1,743 × 1.2 ≈ 2,091 calories/day - showing how a low activity level keeps TDEE close to BMR.
What Affects Your BMR
- Muscle mass. Muscle tissue burns significantly more calories at rest than fat tissue, so more lean mass raises BMR.
- Age. BMR tends to decline gradually with age, largely due to natural loss of muscle mass over time.
- Sex. Men typically have a higher BMR than women of the same age, height, and weight, mainly due to higher average lean body mass.
- Genetics and hormones. Thyroid function and genetic variation can shift metabolic rate meaningfully above or below formula-based estimates.
- Body size. Larger bodies generally have a higher absolute BMR simply because more tissue requires more energy to maintain.
BMR, TDEE, and Weight Loss
Weight loss plans should create a deficit relative to TDEE (your full daily burn), not BMR (your resting burn alone). Eating below BMR removes the calories your body needs even at complete rest, which can slow metabolism over time, increase muscle loss, and is difficult to sustain. A common, more sustainable approach is a moderate deficit of roughly 15% to 25% below TDEE.
Similarly, for weight gain or muscle building, a moderate surplus above TDEE (not just above BMR) is the standard recommendation, since TDEE already reflects your true total energy needs including activity.
How Accurate Are BMR Formulas?
Formula-based BMR estimates are generally accurate within about 10% of measured resting metabolic rate for most people, which is precise enough for general nutrition and fitness planning. However, they are population averages - individual results can vary due to genetics, muscle mass, medical conditions, and hormone levels that a four-input formula cannot capture. The only way to get a lab-precise number is indirect calorimetry, a clinical test that measures actual oxygen consumption and carbon dioxide production at rest.
Common Mistakes
- Confusing BMR with TDEE. Eating at your BMR alone ignores the calories your daily activity actually requires.
- Choosing the wrong activity multiplier. Most people overestimate their activity level, which inflates the TDEE estimate and can stall weight loss.
- Chasing an extreme calorie deficit. Cutting far below TDEE (or below BMR) tends to backfire through muscle loss, fatigue, and poor adherence.
- Ignoring muscle mass changes. BMR should be recalculated periodically, especially after meaningful weight or muscle mass changes.
- Treating the formula as exact. Formula-based BMR is a solid starting estimate, not a lab-precise number - adjust based on real-world results over a few weeks.
Glossary
- Basal Metabolic Rate (BMR)
- Calories burned at complete rest to maintain essential body functions.
- Total Daily Energy Expenditure (TDEE)
- Total calories burned in a day, including BMR plus all activity and digestion.
- Mifflin-St Jeor equation
- The most widely recommended modern formula for estimating BMR from age, sex, height, and weight.
- Activity multiplier
- A factor applied to BMR (ranging roughly 1.2 to 1.9) to estimate TDEE based on typical weekly activity.
- Resting metabolic rate (RMR)
- Similar to BMR but measured under slightly less strict conditions; often used interchangeably in practice.
- Indirect calorimetry
- A clinical test measuring oxygen and carbon dioxide exchange to precisely determine resting metabolic rate.
- Lean body mass
- Total body weight minus fat mass; a key driver of BMR since muscle burns more calories than fat at rest.
Frequently Asked Questions
Q: What is BMR and how is it calculated?
A: Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to maintain basic life functions like breathing, circulation, and cell repair. The most widely used modern formula is the Mifflin-St Jeor equation: for men, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5, and for women, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161.
Q: What is the difference between BMR and TDEE?
A: BMR is the calories burned at complete rest with zero activity, while TDEE (Total Daily Energy Expenditure) is your full daily calorie burn including all movement, exercise, and digestion. TDEE is calculated by multiplying BMR by an activity multiplier ranging from about 1.2 for a sedentary lifestyle to 1.9 for a very physically active one.
Q: Is the Mifflin-St Jeor equation the most accurate BMR formula?
A: Among widely used equations, Mifflin-St Jeor (published in 1990) is generally considered the most accurate for the general population and has replaced the older Harris-Benedict equation (1919, revised 1984) in most clinical and fitness settings, since multiple validation studies have found it produces smaller average errors compared to measured resting metabolic rate.
Q: Why do men and women have different BMR formulas?
A: Men and women have different average body compositions at the same height and weight - men typically carry more lean muscle mass, which burns more calories at rest than fat tissue does. The Mifflin-St Jeor equation accounts for this by adding 5 for men and subtracting 161 for women in the final step, reflecting the average metabolic difference measured across large study populations.
Q: Should I eat exactly at my BMR to lose weight?
A: No. Eating at or below your BMR is not recommended for weight loss, since your body needs additional energy above BMR for daily movement, digestion, and normal activity - eating too far below your total energy needs can slow metabolism, cause muscle loss, and is generally unsustainable. Sustainable weight loss plans typically target a moderate deficit below TDEE (total daily calories), not below BMR.
Q: What factors affect BMR besides age, sex, height, and weight?
A: Beyond the four inputs used in standard formulas, BMR is also influenced by muscle mass (more muscle raises BMR), genetics, hormonal factors such as thyroid function, body temperature, pregnancy, and even environmental temperature. These factors are not captured by simple equations, which is why lab-measured resting metabolic rate (via indirect calorimetry) is more precise than any formula-based estimate.
This calculator provides estimates for informational and educational purposes only and does not constitute medical or nutritional advice. It uses the Mifflin-St Jeor equation and standard activity multipliers, which are population-average formulas and do not account for individual genetics, medical conditions, hormone levels, or precisely measured body composition. Consult a physician or registered dietitian before making significant changes to your diet or exercise routine. Sources: Mifflin MD, St Jeor ST, et al. (1990) resting metabolic rate equation; Academy of Nutrition and Dietetics energy estimation guidance; standard TDEE activity multiplier methodology used across sports nutrition.