Health

Basal Metabolic Rate (BMR) and TDEE Calculator

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Reviewed by: Martín Rodríguez (política editorial ) · Last reviewed: 20 may 2026

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Your Basal Metabolic Rate (BMR) is the calories your body burns at complete rest. It's 60–70% of total daily expenditure; TDEE adds activity, NEAT, and the thermic effect of food. This calculator uses the Mifflin-St Jeor equation (1990) — the equation endorsed by the Academy of Nutrition and Dietetics (the US's largest registered-dietitian body) for healthy non-obese adults, with ±10% accuracy. The USDA Dietary Guidelines for Americans 2020–2025 use the same energy framework. Outputs include kcal/day for maintenance, a 500 kcal/day deficit (≈ 1 lb/week of fat loss), and a 300 kcal/day surplus for lean gain.

Last reviewed: May 19, 2026 Verified by Martín Rodríguez Source: Academy of Nutrition and Dietetics — Adult Weight Management Evidence-Based Guideline, USDA & HHS — Dietary Guidelines for Americans 2020–2025, NIH National Heart, Lung, and Blood Institute — Body Weight Planner & Energy Balance, Mifflin MD, St Jeor ST — A new predictive equation for resting energy expenditure in healthy individuals (Am J Clin Nutr, 1990), CDC — Healthy Weight, Nutrition, and Physical Activity 100% private

When to use this calculator

You're starting a diet and need to know how many calories to eat to lose weight without losing muscle mass.
You've plateaued and want to recalculate your expenditure with your current weight (BMR drops as you lose weight).
You want to clean bulk: 200–400 kcal surplus above your TDEE.
You're a nutritionist or personal trainer and need a fast, reliable calculation for clients.
You're entering perimenopause/menopause and noticed your metabolism changed: recalculate with updated data.

Example: 35-year-old woman, 68 kg, 165 cm, moderate activity

BMR Mifflin-St Jeor (women): 10 × 68 + 6.25 × 165 − 5 × 35 − 161 = 680 + 1,031.25 − 175 − 161 = 1,375 kcal.
Moderate factor (4–5 days/wk): 1.55.
TDEE: 1,375 × 1.55 = 2,131 kcal/day.
To lose weight (−500): 1,631 kcal/day.
To gain muscle (+300): 2,431 kcal/day.

Result: Maintenance: 2,131 kcal/day for a 35-year-old, 150 lb (68 kg), 5'5" (165 cm) female with moderate activity. To lose ~1 lb/week, eat 1,631 kcal/day; for a lean bulk, 2,431 kcal/day with high protein per USDA Dietary Guidelines.

How it works

2 min read

What Is BMR

BMR represents the minimum energy to maintain vital functions: heartbeat, breathing, body temperature (~98.6°F), brain function, cellular repair. In healthy adults:

Component	% of TDEE
BMR (basal)	60–70%
NEAT (non-exercise activity)	15–20%
TEF (thermic effect of food)	10%
EAT (formal exercise)	5–15%

Mifflin-St Jeor Formula (1990)

More accurate than Harris-Benedict (1919) when validated on modern populations. Has a ±10% error in 82% of cases per the Academy of Nutrition and Dietetics.

Men:

BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5

Women:

BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Activity Factors (TDEE)

Level	Factor	Concrete example
Sedentary	1.2	Desk job 8 hours, no gym
Light	1.375	Walking, yoga, pilates 1–3x/wk
Moderate	1.55	Gym or running 4–5x/wk
High	1.725	Intense daily training
Very high	1.9	Pro athlete or heavy physical labor

TDEE = BMR × activity factor

Caloric Deficit and Surplus

1 lb of body fat ≈ 3,500 kcal stored.

Goal	Strategy	Weekly result
Lose weight	−300 to −500 kcal/day	0.6–1 lb ↓
Maintain	TDEE exact	0 lb
Gain muscle	+200 to +400 kcal/day	0.4–0.8 lb ↑

Safety Rule

Never drop below 1,200 kcal/day for women or 1,500 kcal/day for men without professional supervision. Deficits greater than 25% of TDEE cause muscle mass loss, fatigue, and rebound.

When to Recalculate

Every 10 kg (22 lb) of weight change (BMR adjusts to the new weight).

Whenever activity level changes.

Every birthday: BMR drops ~1% per year after age 20.

After prolonged illness or hormonal changes (pregnancy, menopause, thyroid treatment).

Other BMR Formulas

Formula	Year	Recommended use
Revised Harris-Benedict	1984	Historical, overestimates ~5%
Mifflin-St Jeor	1990	Standard for healthy adults
Katch-McArdle	1996	With known body fat %, ideal for athletes
Cunningham	1980	Only lean mass, high-level athletes

If you know your body fat %, Katch-McArdle is more accurate:

BMR = 370 + 21.6 × lean_mass(kg)

Common Mistakes

1. Overestimating activity: if you gym 3x/week but sit 8 hours, you're 'light,' not 'moderate.'
2. Not recalculating as you lose weight: the same deficit doesn't yield the same results at 90 kg vs. 75 kg.
3. Underestimating intake: dressings, oil, sugary drinks, and alcohol add more than they appear.
4. Expecting linear results: weight varies ±2 kg per day from water, glycogen, hormones. Track weekly average.
5. Ignoring strength training: cardio + deficit alone can lead to 'skinny fat.' Always add strength training.

Frequently asked questions

What's the difference between BMR and TDEE?

BMR is your expenditure at absolute rest (as if you slept 24 hours). TDEE adds physical activity, NEAT, and the thermic effect of food on top. TDEE = BMR × activity factor (1.2 to 1.9 depending on how active you are).

Why use Mifflin-St Jeor and not Harris-Benedict?

Mifflin-St Jeor was validated in 1990 with modern population data and predicts real BMR with ±10% error in 82% of cases, better than Harris-Benedict per the Academy of Nutrition and Dietetics. Harris-Benedict tends to overestimate by 5%.

How much caloric deficit is safe for losing weight?

A 300–500 kcal/day deficit is the safe, sustainable range (0.6–1 lb/week). Never drop below 25% of your TDEE or 1,200 kcal/day (women) or 1,500 (men) without medical follow-up.

Can you gain muscle and lose fat at the same time?

Yes, it's called body recomposition and works especially for: (1) beginners, (2) overweight people starting strength training, (3) those returning after a break. Requires maintenance or slight deficit (−200 kcal) with high protein (1.8–2.2 g/kg) and strength training 3–5x/week.

Why does my metabolism seem slower than before?

Three likely causes: (1) aging (BMR drops ~1%/year after 20), (2) muscle mass loss from sedentary lifestyle, (3) metabolic adaptation from very restrictive diets. The fix is always the same: strength training + high protein.

Does the calculator work during menopause?

Yes, but during menopause BMR drops an additional 3–5% due to hormonal changes (declining estrogen, loss of lean mass). Recommended to recalculate every 6 months, prioritize high protein, and strength training to counter sarcopenia. Consult a nutritionist or endocrinologist.

How do I adjust if I have lots of muscle mass?

If you know your body fat % (via body fat calculator, bioimpedance, or skinfolds), use the Katch-McArdle formula: BMR = 370 + 21.6 × lean mass. More accurate for athletes than Mifflin-St Jeor because it doesn't penalize muscle mass.

Are the results medical?

No. They are estimates with ±10% margin. The calculator is useful for planning and monitoring, but medical decisions (bariatric surgery, obesity treatment, eating disorders, diabetes) require a professional. Consult a registered dietitian.