Quick facts
- •BMR is the energy your body uses at complete rest. For most people it is around 60% to 70% of total daily calorie burn.
- •The Mifflin-St Jeor formula for men is 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. For women, subtract 161 instead of adding 5.
- •For a 30-year-old man, 175 cm and 75 kg, the three formulas give about 1,699, 1,763 and 1,747 calories (Katch-McArdle at 15% body fat).
- •Muscle uses more energy at rest than fat, but the gap is modest: roughly 13 calories per kg a day against about 4.5 for fat tissue.
- •BMR tends to fall with age, mainly as muscle is lost. Studies suggest muscle mass can decline roughly 3% to 8% per decade after 30 without strength training.
Quick reference
| Formula | Year and idea | Best for | Inputs |
|---|---|---|---|
| Mifflin-St Jeor | 1990. Built from a larger, more modern sample and widely validated | Most adults, and the default choice | Weight, height, age, sex |
| Harris-Benedict | 1919, revised 1984. Historically important, tends to run higher | Comparing with older tools | Weight, height, age, sex |
| Katch-McArdle | Uses lean body mass instead of total weight | Lean or muscular people who know their body fat | Weight and body fat % |
Worked examples
A 30-year-old man, 175 cm and 75 kg: what is his BMR?
About 1,699 with Mifflin-St Jeor
10 × 75 + 6.25 × 175 − 5 × 30 + 5 = 1,698.75. The revised Harris-Benedict gives about 1,763. Katch-McArdle at 15% body fat gives about 1,747, and at 20% body fat about 1,666. Spread across formulas is about 65 calories.
Why is my BMR different from a friend with the same stats?
Two formulas cannot see your muscle
Mifflin-St Jeor and Harris-Benedict only use weight, height, age and sex. Two people who match on those but carry different amounts of lean mass will have different real BMRs. Katch-McArdle uses lean mass, so it captures some of that.
How do I turn BMR into daily calories?
Multiply by an activity factor from 1.2 to 1.9
A BMR of 1,699 times 1.55 (moderate exercise) is about 2,633 calories a day to maintain weight. The factor is a rough guess, so check your results over two weeks.
How does BMR change as I lose weight?
It falls a little, mainly because you are smaller
In the Mifflin-St Jeor equation each kilogram of body weight is worth about 10 calories a day. Losing 10 lb (4.5 kg) lowers BMR by about 45 calories and maintenance by about 70 at moderate activity.
Trusting a BMR number without knowing the formula
The mistake
Comparing numbers from different apps as if they came from the same method.
Do this instead
Check which equation each tool used. Use Katch-McArdle if you know your body fat, and Mifflin-St Jeor if you do not. Compare at least two before settling on a target.
Why it matters
A 100 calorie error is about 0.2 lb a week, or roughly 10 lb a year. Small differences in your starting number add up if you never check results.
Why a bmr calculator matters
Every calorie target starts here
- •Your TDEE is BMR multiplied by an activity factor. An error in BMR carries into every number after it.
- •Knowing which formula an app used helps you compare results from different tools.
- •This calculator shows three formulas together so you can see the spread.
- •A spread of 50 to 100 calories is normal and shows the uncertainty in any estimate.
Is a slow metabolism really the problem?
- •People of the same size can differ by a few hundred calories a day in real BMR, mostly from body composition and genetics.
- •Most of the difference between people comes from body size and muscle, not a faulty metabolism.
- •If you have fatigue, cold intolerance or unexplained weight change, ask a doctor about a thyroid check.
- •Cutting calories hard because of an assumed slow metabolism usually backfires.
How BMR changes over time
- •A smaller body needs fewer calories, so BMR drops as you lose weight.
- •Muscle loss with age lowers BMR over decades.
- •Strength training and enough protein help keep muscle.
- •BMR is an estimate that moves with your body, not a fixed trait.
What makes this bmr calculator useful
Three formulas side by side
See Mifflin-St Jeor, Harris-Benedict and Katch-McArdle at once, so you know how much uncertainty is in your number.
Body-fat option
Enter body fat percentage to include Katch-McArdle, which is often better for lean or muscular people.
Activity table
See your estimated daily calories at each activity level, based on your own BMR.
Plain-language summary
A short sentence explaining what the number means and how to use it.
Professional applications
Nutrition counselling
Dietitians use BMR as a starting point, then adjust using the client’s actual weight trend.
A client whose results stall gets a small adjustment, not a big cut.
Sports performance
Coaches use body-fat-aware formulas for athletes, where lean mass matters more than total weight.
A lean athlete may get a higher estimate from Katch-McArdle than from Mifflin-St Jeor.
Clinical nutrition
Clinicians sometimes measure energy use directly in hospital settings, because equations can be off for ill patients.
Indirect calorimetry measures oxygen use to find real resting energy expenditure.
Historical context
Frequently asked questions
What is BMR, exactly?+
Basal metabolic rate is the energy your body needs at rest for breathing, circulation, temperature and cell repair. It is measured in calories per day and is the base of your daily energy budget.
Which BMR formula is most accurate?+
Mifflin-St Jeor is the best default for the general population. Katch-McArdle can be better for lean, muscular people who know their body fat percentage, but only if that figure is reliable. Harris-Benedict is mainly of historical interest and tends to run higher.
How can I increase my BMR?+
Build or keep muscle with strength training and eat enough protein. The effect is modest, because muscle burns about 13 calories per kg a day at rest, but it is real over months. Avoid very low calorie diets that cost muscle.
What is the difference between BMR and TDEE?+
BMR is what you burn at rest. TDEE, total daily energy expenditure, is BMR plus everyday movement, exercise and the energy used digesting food. TDEE is the number to use for a calorie target.
What this calculator cannot do+
It cannot measure your true BMR, which needs a lab test. It does not account for thyroid conditions, medicines, pregnancy or growth in teenagers. Treat the number as an estimate and use real-world results to adjust.