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How many calories your body burns at complete rest

Compare Mifflin-St Jeor and revised Harris-Benedict for resting burn

These calculators provide estimates based on population-level formulas and do not replace assessment by a dietitian, physician or exercise professional.

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Biological sex
Metabolic formulas use different constants by biological sex.

Turn your BMR into a daily target in FITTA

FITTA calculates your basal rate with Mifflin-St Jeor and adjusts calories and macros to what you eat and lift.

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Practical guide

How to use FITTA better.

Basal metabolic rate (BMR) is the energy your body uses just to stay alive: breathing, circulation, core temperature, and cell turnover, while fasting and fully at rest. It does not include walking, training, digestion, or the thermic effect of food. This calculator compares Mifflin-St Jeor (1990) with the Harris-Benedict revision by Roza and Shizgal (1984). Both take sex, body weight, height, and age. The output is a population-level estimate in kcal per day, not a calorimetry test, and it does not replace a dietitian or physician.

What BMR actually measures

BMR is the minimum energy cost of an adult about 12 hours fasted, awake, in a thermoneutral room, and still. Labs measure it with indirect calorimetry. The equations on this page estimate it from sex, mass, stature, and age. In clinic the closer everyday number is resting metabolic rate (RMR), typically 5 to 10 percent above true BMR. Mifflin-St Jeor tracks RMR better than lab BMR, even though most tools still label the result BMR.

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Left out: the thermic effect of food (8 to 12 percent of daily energy), structured exercise, NEAT, and the adaptive drop of a long deficit. That is why BMR is often 60 to 75 percent of TDEE in sedentary adults, and a smaller share in people who train.

How to calculate BMR with Mifflin-St Jeor

Mifflin, St Jeor, and colleagues published in 1990 the regression with the lowest average error in healthy adults, and it is the headline equation here. Weight in kilograms, height in centimeters, age in years. Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5. Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161. Convert first if needed: pounds ÷ 2.205, inches × 2.54. The calculator is metric.

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A man at 80 kg (176 lb), 175 cm (5 ft 9 in), age 30: 10 × 80 + 6.25 × 175 − 5 × 30 + 5 = 800 + 1,093.75 − 150 + 5 = 1,748.75 kcal. A woman at 65 kg (143 lb), 165 cm (5 ft 5 in), age 28: 10 × 65 + 6.25 × 165 − 5 × 28 − 161 = 650 + 1,031.25 − 140 − 161 = 1,380.25 kcal. FITTA calculates with these coefficients and rounds to the nearest whole kcal.

Revised Harris-Benedict and how the two compare

The original Harris-Benedict equations (1918–1919) overestimate modern expenditure. Roza and Shizgal republished the coefficients in 1984, and this page uses that revision. Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age. Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age.

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Same 80 kg, 175 cm, 30-year-old man: 88.362 + 13.397 × 80 + 4.799 × 175 − 5.677 × 30 = 88.362 + 1,071.76 + 839.825 − 170.31 = 1,829.6 kcal. Same 65 kg, 165 cm, 28-year-old woman: 447.593 + 9.247 × 65 + 3.098 × 165 − 4.330 × 28 = 447.593 + 601.055 + 511.17 − 121.24 = 1,438.6 kcal. The revision sits 60 to 80 kcal above Mifflin, about 4 to 5 percent. If body-fat percentage is known, Katch-McArdle (370 + 21.6 × lean mass in kg) is usually tighter for extreme physiques, because neither formula here can see composition.

How to read the number

The headline is Mifflin-St Jeor in kcal per day. Harris-Benedict is the cross-check: a gap above 5 to 8 percent means you should verify sex, weight, and height. BMR divided by 24 is the hourly cost of complete rest, not overnight sleep.

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Treat BMR as a floor. TDEE comes from a PAL factor: 1.2 sedentary; 1.375 light training 1 to 3 days a week; 1.55 for 3 to 5 sessions; 1.725 hard daily training; 1.9 high-volume athletes. Deficit and surplus come off TDEE. At 1,750 kcal BMR and PAL 1.55, maintenance is about 2,710 kcal; a 400 to 500 kcal cut starts there. Outside a common adult band of 1,100 to 2,400 kcal, recheck the inputs. Two bodies at the same weight can differ 10 to 15 percent from lean mass, hormones, and diet history.

Common mistakes when you calculate BMR

Treating BMR as the day’s calorie budget is the costliest error: eating at basal for weeks drives an aggressive deficit, lean-mass loss, and a further drop the equation does not model. Mixing units is next: pounds where the formula expects kilograms inflate the result about 2.2 times; height in meters instead of centimeters swaps 6.25 × 175 for 6.25 × 1.75.

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Using the 1919 original in place of the 1984 revision moves the result by tens of kcal. Dropping Mifflin’s sex term (+5 or −161) shifts the answer by 166 kcal. Both equations were fit on adults; in adolescents, pregnancy, frail older adults, or untreated thyroid disease the error grows.

  • Do not use BMR as your daily calorie target
  • Convert lb and inches to kg and cm before the formula
  • Confirm you are on the 1984 revision, not the 1919 original
  • Recalculate after body weight moves about 5 kg (11 lb)
  • If body composition is extreme, prefer a lean-mass equation

Putting BMR to work in training and diet

BMR barely moves from one session to the next. TDEE is what changes quickly, through training volume and NEAT. Protein at 1.6 to 2.2 g per kg (about 0.7 to 1.0 g per lb) plus progressive strength work holds lean mass, which is what the basal rate tracks over months. Excess cardio without replacing the energy can suppress NEAT and erase a planned deficit.

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For fat loss, cut 300 to 500 kcal from TDEE and watch a 14-day weight average. If the scale does not move and adherence is real, PAL was high, not BMR broken. For muscle gain, add 200 to 400 kcal to TDEE. Recalculate every 4 to 6 weeks or after about 5 kg (11 lb): on Mifflin, 5 kg is 50 kcal per day. In the app, FITTA calculates basal rate with the same coefficients and ties it to logged meals, water, and sessions.

Frequently asked questions

What is basal metabolic rate

It is the energy, in kcal per day, the body spends to keep vital functions running while fasting and fully at rest: breathing, heartbeat, temperature, and cell turnover. It excludes training, walking, digestion, and the thermic effect of food. In sedentary adults it is often 60 to 75 percent of total expenditure. Calculators estimate it; only indirect calorimetry measures it.

How do I calculate BMR

You need sex, weight in kg, height in cm, and age. Mifflin-St Jeor is 10 times weight plus 6.25 times height minus 5 times age, then +5 for men or −161 for women. Revised Harris-Benedict uses intercepts of 88.362 and 447.593 with its own weight, height, and age coefficients. Convert pounds and inches first. This page runs both equations.

Which BMR formula is most accurate

In healthy adults, Mifflin-St Jeor (1990) has the lowest average error in Frankenfield’s reviews and is the equation this calculator leads with. Revised Harris-Benedict (Roza and Shizgal, 1984) usually sits a few percent higher. If you know body-fat percentage, Katch-McArdle, which uses lean mass, tightens the estimate for very lean or higher-fat bodies.

What is the difference between BMR and TDEE

BMR is expenditure at complete rest. TDEE, total daily energy expenditure, multiplies BMR by an activity factor and, in practice, also absorbs the thermic effect of food and NEAT. Diet and training plans sit on TDEE. Eating at BMR is an extreme deficit and is not the protocol on this page.

Mifflin-St Jeor vs Harris-Benedict

Use Mifflin-St Jeor as the anchor and revised Harris-Benedict only as a cross-check. The 1918–1919 original is outdated and overestimates modern expenditure. Gaps up to 5 percent between Mifflin and the 1984 revision are expected. A larger split usually means a bad input, not a broken metabolism.

Why is my BMR so low

It usually means less lean mass, shorter stature, older age, or female sex, because those variables enter with a negative sign or a smaller coefficient. It does not diagnose hypothyroidism. Repeated crash diets can pull real expenditure below the prediction. If an adult result lands under about 1,100 kcal, recheck weight, height, and sex before you read anything into it.

How to increase basal metabolic rate

The lever the formula can see is body mass, especially lean mass. Progressive strength training, enough protein, and leaving a deep deficit recover part of the rate. Cardio alone moves TDEE more than BMR. Caffeine and fat burners nudge RMR for hours, not the equation’s coefficients. Recalculate after you gain or lose about 5 kg (11 lb).

Keep exploring

TDEE Calculator

Estimate daily calorie burn with Mifflin-St Jeor and a 1.2–1.9 activity factor

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Daily target for fat loss, maintenance or muscle gain, plus time to goal weight

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Estimate body fat from neck, waist, and hip with the U.S. Navy formula

These calculators provide estimates based on population-level formulas and do not replace assessment by a dietitian, physician or exercise professional.