What is BMR (basal metabolic rate)?

BMR is the calories your body burns at complete rest to run vital organs — breathing, circulation, brain, liver, kidneys — usually measured after overnight fast in a neutral room. It is not total daily burn. Our default male (25 y, 180 cm, 60 kg, Mifflin-St Jeor) shows BMR 1605 kcal/day; with moderate activity (×1.55) that rises to about 2488 kcal/day maintenance. Most people spend roughly 60–75% of total energy on resting metabolism, not the simplified “70%” rule alone.

How do you calculate BMR with the Mifflin-St Jeor equation?

Men: BMR = 10×W(kg) + 6.25×H(cm) − 5×A + 5. Women: same but −161 instead of +5. Worked example — 60 kg, 180 cm, age 25 male: 10(60) + 6.25(180) − 5(25) + 5 = 600 + 1,125 − 125 + 5 = 1605 kcal/day. Female 55 kg, 165 cm, age 30: 1270 kcal/day. This 1990 equation is the default in most nutrition apps and dietitian practice for general adults.

Mifflin-St Jeor vs Harris-Benedict — which is more accurate?

For the same person (60 kg, 180 cm, 25 y male), Mifflin = 1605 kcal/day vs revised Harris-Benedict = 1614 kcal/day — often within ~50 kcal but Harris can read slightly higher. Meta-analyses favor Mifflin for modern Western adults; Harris (1984 revision) is fine for comparison. Neither replaces indirect calorimetry — expect ±10–15% individual error.

What is the Katch-McArdle formula and when should I use it?

BMR = 370 + 21.6 × lean body mass (kg), where LBM = weight × (1 − body fat%). At 60 kg and 20% fat, LBM = 48 kg → BMR ≈ 1407 kcal/day vs Mifflin 1605 for the same person. Use Katch when you have a reliable body-fat reading (DEXA, hydrostatic, skilled calipers). Lean lifters often prefer it; without BF%, we fall back to Mifflin.

What is the difference between BMR and RMR?

BMR is stricter (longer fast, fully rested, lab conditions). RMR (resting metabolic rate) is measured under relaxed but less rigid conditions and is typically 5–10% higher than BMR. In everyday fitness, people say “BMR” when they mean resting burn. This calculator estimates resting expenditure — treat output as RMR-like for meal planning.

How many calories should I eat to lose weight?

Start from maintenance TDEE, then subtract 300–500 kcal/day for ~0.3–0.5 kg (0.6–1 lb) fat loss per week. Example: moderate activity 2488 kcal maintenance → 1988 kcal/day (−500) ≈ 1 lb/week loss (rule of thumb: 3,500 kcal ≈ 1 lb fat). Never go below ~1,200 kcal (women) or ~1,500 kcal (men) without medical supervision. Track scale trend for 2–3 weeks and adjust.

How accurate are online BMR calculators?

Formula estimates cluster around population averages but miss genetics, thyroid status, sleep, and muscle mass. A 2005 review (Speakman et al.) noted ~26% unexplained variance between individuals even when height, weight, age, and sex are controlled. Use BMR as a starting calorie target, then adjust ±100–200 kcal based on whether weight rises or falls over 2–3 weeks.

Why does BMR decrease with age?

After ~20–30, lean mass often declines and organ metabolism slows — same weight at 50 typically burns fewer calories at rest than at 25. Example: male 60 kg at 180 cm drops ~5 kcal per year in the Mifflin age term (−5×A). Resistance training preserves lean mass and can partially offset age-related BMR drop.

Does muscle mass increase BMR?

Yes. Muscle is metabolically active (~13 kcal/kg/day at rest vs ~4.5 for fat). Two people at 80 kg with different body fat can have different BMR — that is why Katch-McArdle uses lean mass. Adding 2–3 kg muscle might raise resting burn ~25–40 kcal/day — modest, but meaningful over years. Heavy lifting also increases post-exercise oxygen consumption (EPOC), which BMR formulas do not include.

Can I use BMR if I am pregnant or under 18?

No — this tool is for adults roughly 15–80 without special metabolic conditions. Pregnancy, breastfeeding, and adolescence need clinician or dietitian plans with higher energy needs. For body composition in teens, use growth-aware tools; for pregnancy calories, consult OB/GYN guidelines.

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Q: How do activity multipliers turn BMR into daily calories (TDEE)?

Multiply BMR by an activity factor. Default BMR 1605 kcal: sedentary ×1.2 = 1926; light ×1.375 = 2207; moderate ×1.55 = 2488; active ×1.725 = 2769; very active ×1.9 = 3050; extra active ×2.0 = 3210. Pick the row that matches your average week, not your hardest day.

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BMR · TDEE · 3 formulas

BMR Calculator — Basal Metabolic Rate & Daily Calories

Free BMR calculator using Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle. Get resting calories and maintenance calories (TDEE) for sedentary through extra-active lifestyles.

Last updated: May 24, 2026

All three BMR formulas compared

Activity table ×1.2 to ×2.0

Metric and US units

Need macros too? Calorie calculator

BMR Calculator

Mifflin-St Jeor, Harris-Benedict, Katch-McArdle & TDEE bands

Unit system

Age

Gender

Height (cm)

Weight (kg)

BMR (selected equation)

1,605 kcal/day

Mifflin

1605

Harris

1614

Katch

1407

Daily calories (TDEE estimate)

Sedentary (×1.2)1,926

Light (×1.375)2,207

Moderate (×1.55)2,488

Active (×1.725)2,769

Very active (×1.9)3,050

Extra active (×2)3,210

Estimates only — adjust ±100–200 kcal based on weekly weight trend.

What This BMR Calculator Shows

BMR (Mifflin)

1605 kcal/day

Male · 25 y · 180 cm · 60 kg

Moderate activity TDEE

2488 kcal/day

BMR × 1.55 · gym 4–5×/week

Formula spread

Mifflin: 1605

Harris: 1614

Katch (20% BF): 1407

Quick examples

Male · 60 kg · 180 cm

1605

BMR kcal

Sedentary ×1.2

1926

kcal/day

Female · 55 kg · 165 cm

1270

BMR kcal

US · 5′10″ · 160 lb

1692

BMR kcal

BMR formulas & activity multipliers

Mifflin-St Jeor walkthrough (default male)

BMR = 10(60) + 6.25(180) − 5(25) + 5 = 600 + 1,125 − 125 + 5 = 1605 kcal/day

Equation comparison

Equation	Formula (male / female)	Best for	Example*
Mifflin-St Jeor	BMR = 10W + 6.25H − 5A + 5 BMR = 10W + 6.25H − 5A − 161	General adults (1990); default in most apps	1605
Revised Harris-Benedict	BMR = 13.397W + 4.799H − 5.677A + 88.362 BMR = 9.247W + 3.098H − 4.330A + 447.593	Legacy comparison; often reads slightly higher	1614
Katch-McArdle	BMR = 370 + 21.6 × lean mass (kg) BMR = 370 + 21.6 × lean mass (kg)	Known body fat %; lean athletes	1407

*60 kg, 180 cm, 25 y male; Katch at 20% body fat

Daily calories by activity (TDEE)

Level	Multiplier	kcal/day*	Typical week
Sedentary	×1.2	1926	Little or no exercise
Light	×1.375	2207	Exercise 1–3 days/week
Moderate	×1.55	2488	Exercise 4–5 days/week
Active	×1.725	2769	Daily or intense 3–4×/week
Very active	×1.9	3050	Intense 6–7 days/week
Extra active	×2	3210	Hard daily training or physical job

*Based on BMR 1605 kcal (Mifflin)

Where calories go (average adult)

Component	Share of TDEE
BMR / resting metabolism	~60–75%
Physical activity (NEAT + exercise)	~15–30%
Thermic effect of food (TEF)	~8–10%

Limitations

Estimates only — individual variance can be ±10–15% vs indirect calorimetry
Does not account for thyroid disease, medications, or menstrual cycle shifts
Katch-McArdle needs accurate body fat %; bad BF% input skews results
Activity multipliers approximate TDEE — track weight trend and adjust
Not for children under 15 or pregnant individuals without clinical guidance

References

Mifflin et al., 1990 — Am J Clin Nutr; predictive equation for resting energy expenditure
CDC — Healthy weightBalancing calories in and out

Worked examples

Female · Mifflin

30 y · 165 cm · 55 kg

1270 kcal BMR

Moderate TDEE: 1969 kcal

Katch-McArdle

60 kg · 20% body fat

1407 kcal BMR

LBM 48 kg

Weight loss math

−500 kcal from moderate TDEE

2488 → 1988 kcal/day

≈ 1 lb/week

Frequently Asked Questions

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