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BMR Calculator (Harris-Benedict): Calories Burned at Rest

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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed: Jun 4, 2026

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Your basal metabolic rate (BMR) is the number of calories your body burns over 24 hours at complete rest just to keep you alive: heart pumping, lungs breathing, brain firing, kidneys filtering, cells dividing. For most adults, BMR accounts for roughly 60 to 70 percent of total daily calorie burn, which is why nailing this number is the first step in any sensible weight loss, weight gain, or body recomposition plan. This calculator runs the Harris-Benedict revised equation, first published in 1919 and revised by Roza and Shizgal in 1984 to better fit modern body sizes. The revised Harris-Benedict formula is still widely used in clinical practice, though research suggests the Mifflin-St Jeor equation (1990) tends to be slightly more accurate for the average non-obese adult; the Academy of Nutrition and Dietetics endorses Mifflin-St Jeor as current best practice. For athletes with known body fat percentage, Katch-McArdle based on lean body mass is more precise. Enter your weight in kilograms, height in centimeters, age in years, and biological sex to get your BMR in kcal/day. The insight panel also shows your estimated Total Daily Energy Expenditure (TDEE) across all five standard activity levels so you can immediately see your maintenance calories.

Last reviewed: June 3, 2026 Verified by Martín Rodríguez Source: Roza AM, Shizgal HM (1984) — The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr 40(1):168-82, Mifflin MD, St Jeor ST, et al. (1990) — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 51(2):241-7, Frankenfield D, Roth-Yousey L, Compher C (2005) — Comparison of predictive equations for resting metabolic rate. J Am Diet Assoc 105(5):775-89, Academy of Nutrition and Dietetics — Adult Weight Management Evidence-Based Nutrition Practice Guideline, American College of Sports Medicine (ACSM) — Position Stand on Nutrition and Athletic Performance 100% private

Your BMR (basal metabolic rate) is the calories your body burns at complete rest. Harris-Benedict revised formula — 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). Example: a 35-year-old man, 81.6 kg, 182.9 cm → 1,861 kcal/day. Multiply BMR by an activity factor (1.2 sedentary to 1.9 extra active) to get your TDEE.

When to use this calculator

Cutting: calculate a 300–500 calorie daily deficit below TDEE to lose roughly 0.5–1 lb of fat per week without crashing metabolism
Bulking: calculate a 250–500 calorie surplus above TDEE to add lean mass while minimizing fat gain
Registered dietitian intake assessment: cross-check a client's reported food log against estimated needs to flag underreporting or chronic underfeeding
Calibrating a fitness tracker: compare Harris-Benedict and Mifflin-St Jeor results against your device's BMR estimate to see if it is over- or underestimating
Pre-bariatric or medical weight loss intake planning: clinicians use BMR as the floor under which medical supervision becomes necessary
Sports nutrition for high school and collegiate athletes: BMR plus activity multiplier gives a starting point for fueling two-a-day training blocks

Example: male, 35 years, 81.6 kg, 182.9 cm

Sex: Male
Weight: 81.6 kg (180 lb)
Height: 182.9 cm (6 ft 0 in)
Age: 35 years
Formula: 88.362 + (13.397 × 81.6) + (4.799 × 182.9) − (5.677 × 35)
= 88.362 + 1,093.19 + 877.88 − 198.70 = 1,860.73 ≈ 1,861 kcal/day

Result: 1,861 kcal/day

How it works

3 min read

What BMR Actually Measures

Basal metabolic rate is the energy your body spends doing nothing. It is measured in a lab after 12 hours of fasting, eight hours of sleep, and 30 minutes of supine rest in a thermoneutral room, typically using indirect calorimetry to capture oxygen consumption and carbon dioxide production. Outside the lab, we estimate it with prediction equations like Harris-Benedict. BMR powers involuntary work: pumping blood (the heart alone burns about 440 calories a day), maintaining body temperature, running the brain (roughly 20 percent of BMR in a healthy adult), kidney filtration, liver detoxification, and constant cellular turnover. It does not include the thermic effect of food (TEF, about 10 percent of daily calories) or any physical activity.

The Harris-Benedict Revised (1984) Formulas

The revised Harris-Benedict equation, the one we run here, uses metric units:

Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)

Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)

Worked example — male, 35 years, 81.6 kg, 182.9 cm (180 lb, 6'0"):

BMR = 88.362 + (13.397 × 81.6) + (4.799 × 182.9) − (5.677 × 35)
    = 88.362 + 1,093.19 + 877.88 − 198.70
    = 1,861 kcal/day

Worked example — female, 35 years, 78 kg, 162 cm:

BMR = 447.593 + (9.247 × 78) + (3.098 × 162) − (4.330 × 35)
    = 447.593 + 721.27 + 501.88 − 151.55
    = 1,519 kcal/day

Mifflin-St Jeor (1990): The More Accurate Modern Standard

Mifflin et al. published an updated equation in 1990 that better matches contemporary adults; the Academy of Nutrition and Dietetics (AND) recommends it as the current best practice for non-obese individuals:

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

For that same 81.6 kg, 182.9 cm, 35-year-old man: BMR = 816 + 1,143.1 − 175 + 5 = 1,789 kcal/day — about 72 calories below Harris-Benedict, which is typical. Both are useful starting points.

From BMR to TDEE: The Activity Multipliers

BMR is calories at rest; total daily energy expenditure (TDEE) adds movement on top. Multiply BMR by one of these activity factors:

Activity level	Factor	Description
Sedentary	1.2	Desk job, little to no exercise
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
Extra active	1.9	Two-a-days or physically demanding job

For the 1,861-calorie BMR man above doing moderate exercise four days a week, TDEE ≈ 1,861 × 1.55 = 2,884 kcal/day. To lose 1 lb per week (3,500 calorie weekly deficit), he would eat about 2,384 kcal/day.

Katch-McArdle: For Athletes With Body Fat Data

If you know your body fat percentage (DEXA, BodPod, or quality bioimpedance), Katch-McArdle uses lean body mass and is more accurate for muscular people:

BMR = 370 + (21.6 × lean body mass in kg)
lean body mass = total weight × (1 − body fat % / 100)

Limitations and When These Equations Fail

Prediction equations assume an average body composition. They systematically underestimate BMR in lean, muscular people and overestimate in people with low lean mass relative to total weight. They also miss meaningful BMR shifts from thyroid disorders (hypothyroidism lowers BMR roughly 10–20%, hyperthyroidism raises it), prolonged severe dieting (adaptive thermogenesis can drop measured RMR 5–15% below predicted), pregnancy and lactation, and certain medications. If your weight is not responding to a calculated calorie target after two to three weeks of consistent tracking, adjust by 100–200 calories and reassess rather than treating the formula as gospel.

Disclaimer: Results are estimates only and do not replace evaluation by a registered dietitian or physician. Do not use for clinical diagnosis, treatment, or medication adjustments.

Frequently asked questions

Harris-Benedict vs Mifflin-St Jeor: which formula is better?

Mifflin-St Jeor (1990) is generally considered more accurate for modern adults and is the formula endorsed by the Academy of Nutrition and Dietetics for non-obese individuals. A 2005 systematic review found Mifflin-St Jeor predicted measured RMR within 10 percent in about 82 percent of non-obese adults, versus around 69 percent for the original Harris-Benedict. The 1984 revised Harris-Benedict closed much of that gap but Mifflin-St Jeor still edges it out on average. Both formulas typically land within 50–100 calories of each other for most adults, so for practical diet planning the difference is small.

Is the BMR calculator accurate for muscular or very lean people?

No, both Harris-Benedict and Mifflin-St Jeor underestimate BMR for muscular individuals because they use total body weight and do not distinguish lean mass from fat mass. A 200 lb male athlete at 10 percent body fat has 180 lb of lean mass; a 200 lb sedentary male at 30 percent body fat has 140 lb of lean mass. Their BMRs can differ by 200 calories or more even though the equation gives the same answer. If you are clearly more muscular than average, use the Katch-McArdle formula with a body fat measurement from DEXA, BodPod, or a quality bioimpedance scan.

What is the BMR for a 180 lb man who is 6'0" tall?

Converting: 180 lb ÷ 2.205 = 81.6 kg; 72 in × 2.54 = 182.9 cm. Using Harris-Benedict revised for a 35-year-old: BMR ≈ 1,861 kcal/day. Using Mifflin-St Jeor: BMR ≈ 1,789 kcal/day. The gap of about 72 calories is normal between the two equations. Age affects this significantly: at 25, the same man would have a Harris-Benedict BMR around 1,917; at 55 it drops to about 1,748.

How many calories do I need to eat to lose 1 lb per week?

One pound of body fat stores about 3,500 calories, so a 500 calorie daily deficit theoretically yields 1 lb of fat loss per week. Start by calculating your TDEE (BMR × activity factor), then subtract 500 calories. For a typical 30-year-old woman, 150 lb (68 kg), 5'5" (165 cm), lightly active: BMR ≈ 1,465 kcal, TDEE ≈ 2,014 kcal, target intake ≈ 1,514 kcal/day. Do not drop below your BMR without medical supervision and aim for no more than 1 percent of body weight lost per week to preserve muscle.

What is the difference between RMR and BMR?

BMR is measured after a 12-hour fast, full overnight sleep, and 30 minutes of supine rest in a thermoneutral lab — the absolute minimum energy to stay alive. RMR is measured under less strict conditions (no overnight fast required) and runs about 10 percent higher than true BMR because digestion and minor activity are still happening. Outside the lab, most calculators and apps use RMR and BMR interchangeably, which is fine for diet planning since the difference is smaller than the equation's prediction error.

Do the activity multipliers overestimate my real calorie burn?

Often, yes. A common pattern: someone with a desk job who works out 4 days a week picks the 1.55 moderately active multiplier, but their non-exercise activity (NEAT) is actually low because they sit for 9 hours. A more conservative starting estimate is to use one tier lower than feels right (e.g., 1.375 instead of 1.55) and adjust based on real-world weight change over 2–3 weeks. Fitness trackers have their own 10–30 percent error margins, especially during strength training.

Should I ever eat below my BMR to lose weight faster?

Generally not, and not without medical supervision. Eating below BMR for extended periods is associated with adaptive thermogenesis (the body lowers RMR 5–15% below predicted to defend against perceived starvation), muscle loss, fatigue, hormonal disruption (lower thyroid output, reduced sex hormones, menstrual irregularity), and increased risk of regaining weight after the diet ends. The Academy of Nutrition and Dietetics recommends a moderate deficit of 500–750 calories below TDEE for most adults wanting to lose weight, which usually keeps intake above BMR.

Does BMR change with age, and can I do anything about it?

BMR drops roughly 1–2 percent per decade after age 20, mostly because of gradual loss of lean muscle mass (sarcopenia) and reduced organ activity. A 60-year-old will typically have a BMR 100–200 calories lower than they did at 25 at the same body weight. Resistance training 2–3 times per week preserves and rebuilds muscle, blunting most of the drop. Adequate protein intake (0.7–1 g per lb of body weight for active adults) supports muscle maintenance. Older adults who lift weights regularly often have BMRs comparable to sedentary 30-year-olds at the same body weight.

How often should I recalculate my BMR?

Recalculate any time your weight changes by more than 5–10 lb, since weight is the largest variable in the equation. Also recalculate on each birthday milestone (every 5 years) to account for age effects. If you are actively dieting or bulking, recalculate every 4–6 weeks as your weight changes. Treat the calculated number as a starting estimate and adjust based on 2–3 weeks of consistent tracking and real weight trend.

How do I convert pounds and inches to use this calculator?

Divide pounds by 2.205 to get kilograms (180 lb ÷ 2.205 = 81.6 kg). Multiply inches by 2.54 to get centimeters (72 in × 2.54 = 182.9 cm). For feet and inches, first convert to total inches: 5'10" = (5 × 12) + 10 = 70 inches × 2.54 = 177.8 cm. You can also use 180 lb ÷ 2.2 as a quick mental shortcut (gives 81.8 kg, close enough for this purpose).