BMR Calculator
Basal Metabolic Rate — calories burned at complete rest
BMR (Mifflin-St Jeor)
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Frequently Asked Questions
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body needs at complete rest to maintain vital functions — breathing, circulation, organ function, temperature regulation. It accounts for 60–70% of total calorie burn.
Which BMR formula is most accurate?
The Mifflin-St Jeor formula (1990) is the most accurate for most adults, validated by the Academy of Nutrition and Dietetics. The Harris-Benedict formula (1919, revised 1984) is slightly less accurate but widely used.
How is BMR different from TDEE?
BMR is calories at rest. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor (1.2–1.9) to account for exercise and daily movement. TDEE is what you actually need to eat to maintain your weight.
Does muscle increase BMR?
Yes. Muscle tissue burns ~6 calories per pound per day at rest, while fat burns ~2 calories per pound. Building muscle is the most effective long-term strategy for raising BMR — this is why strength training helps with fat loss maintenance.
BMR vs TDEE at a Glance
Calories at complete rest
Daily movement, not exercise
Exercise calories
Digesting food
Mifflin-St Jeor Formula
Most accurate for non-athletes (1990)
Men: 10W + 6.25H − 5A + 5
Women: 10W + 6.25H − 5A − 161
W = kg, H = cm, A = age
Typical BMR by Profile
What is BMR and Why Does It Matter?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns every day just to stay alive — even if you did absolutely nothing but lie in bed. It powers your heartbeat, breathing, brain activity, hormone production, and all cellular functions.
BMR is the foundation of all calorie calculations. Once you know your BMR, you can multiply it by your activity level to get your TDEE (Total Daily Energy Expenditure) — the actual number of calories you burn each day. From there, you can set precise targets for weight loss, maintenance, or muscle gain.
Mifflin-St Jeor vs Harris-Benedict: Which Is Better?
| Factor | Mifflin-St Jeor | Harris-Benedict |
|---|---|---|
| Year developed | 1990 | 1919 (revised 1984) |
| Accuracy (vs indirect calorimetry) | ±10% | ±12–14% |
| Best for | Most non-athletic adults | General population |
| Endorsed by | Academy of Nutrition & Dietetics | Widely used historically |
| Recommendation | ✓ Use this one | Good secondary reference |
What Factors Affect Your BMR?
Age
BMR decreases roughly 2% per decade after age 20 as muscle mass naturally declines (sarcopenia).
Sex
Men typically have 5–10% higher BMR than women of the same weight and height due to greater muscle mass.
Body composition
Muscle burns ~3× more calories at rest than fat. Two people with the same weight but different body fat % have very different BMRs.
Height
Taller people have more surface area and more tissue to maintain, so BMR scales with height.
Hormones
Thyroid hormones (T3/T4) directly regulate metabolic rate. Hypothyroidism lowers BMR; hyperthyroidism raises it.
Genetics
Genetic variation in metabolic rate can account for ±200–400 cal/day between individuals of similar size.
How to Use BMR for Weight Loss
Your BMR sets the floor — you should never eat below your BMR for extended periods, as this can trigger metabolic adaptation (your body lowering its metabolic rate to match your intake). This is why crash diets often backfire.
The correct approach: calculate TDEE from your BMR (use the TDEE Calculator), then create a moderate deficit of 15–25% below TDEE. This preserves muscle, keeps energy levels up, and produces sustainable fat loss of 0.5–1 lb per week.