BMR (basal metabolic rate) is the number of calories your body burns at complete rest — typically 60 to 70 percent of everything you burn in a day. This free calculator estimates it with the validated Mifflin-St Jeor equation and the classic Harris-Benedict formula; multiply the result by your activity level to get the TDEE that real calorie plans are built on.
Before you plan a single meal or workout, one number sits underneath everything: your basal metabolic rate. BMR is the energy your body spends just existing — heart beating, lungs breathing, brain thinking, cells repairing — before you take a single step. This BMR calculator estimates yours with the two classic equations, and the guide explains what BMR means, how to calculate it by hand, how it differs from RMR and TDEE, and what actually moves it.
Basal Metabolic Rate (BMR)
Mifflin-St Jeor: calories burned at complete rest.
What is BMR — basal metabolic rate?
Basal metabolic rate is the number of calories your body burns at complete rest in a neutral environment: the cost of being alive. It typically accounts for 60–70% of everything you burn in a day — more than most people’s exercise by a wide margin. The biggest driver is fat-free mass: organs and muscle are metabolically expensive tissue, which is why BMR differs so much between bodies of the same weight and why preserving muscle matters in every diet.
How to calculate BMR: the two standard equations
Mifflin-St Jeor equation (recommended)
Developed in 1990 and repeatedly validated as the most accurate standard prediction for modern adults:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Harris-Benedict equation (the classic)
Published in 1919 and revised in 1984, the Harris-Benedict equation remains widely used; it tends to estimate slightly higher than Mifflin-St Jeor for many adults:
- Men: BMR = 88.362 + 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age
- Women: BMR = 447.593 + 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age
This calculator shows both, and the difference between them is a useful reminder that every formula is an estimate: laboratory measurement (indirect calorimetry) remains the only true test, with equations landing within about ±10% for most people.
Typical BMR values by profile
| Profile | Approx. BMR (Mifflin-St Jeor) |
|---|---|
| Woman, 30, 60 kg, 165 cm | ~1,320 kcal/day |
| Woman, 50, 70 kg, 165 cm | ~1,320 kcal/day |
| Man, 30, 80 kg, 180 cm | ~1,780 kcal/day |
| Man, 60, 85 kg, 175 cm | ~1,650 kcal/day |
Two patterns worth noticing: BMR declines gently with age (roughly 1–2% per decade after early adulthood, driven largely by muscle loss), and body size dominates — a bigger body simply costs more to run.
BMR vs RMR: is there a difference?
Resting metabolic rate (RMR) is BMR’s practical cousin: measured under looser conditions (resting, but not the strict overnight-fasted laboratory protocol), it runs a few percent higher. In everyday use — and in most calculators — the terms are interchangeable; an RMR calculator and a BMR calculator will hand you essentially the same planning number.
BMR vs TDEE: which number do you plan with?
BMR is the floor; TDEE is the total. Multiply BMR by an activity factor (1.2 sedentary through 1.9 extremely active) and you get your total daily energy expenditure — the number meal plans are actually built on. Rules of thumb that keep plans sensible:
- Weight goals are set relative to TDEE, not BMR — see our TDEE calculator.
- Chronic intakes at or below BMR are aggressive territory best supervised by professionals.
- When a diet stalls, recheck TDEE — a lighter body has a lower BMR, so old targets quietly expire.
What raises or lowers your basal metabolic rate
| Factor | Effect on BMR | Honest size of the effect |
|---|---|---|
| Muscle mass | Raises | The one factor you meaningfully control — build and keep it |
| Ageing | Lowers | ~1–2% per decade, mostly via muscle loss — trainable |
| Thyroid function | Either | Genuinely large — an underactive or overactive thyroid shifts metabolism and deserves testing, not guessing |
| Severe dieting | Lowers | Modest adaptive slowdown; normalises with sensible eating |
| Genetics | Either | Real but smaller than diet culture claims |
| Metabolism boosters (supplements, foods) | — | Marketing: effects are trivial or unproven |
When a low BMR is a medical question
Formulas assume health. If you gain weight on genuinely modest intake, feel cold, fatigued or notice hair thinning and constipation, the question is not your willpower but your thyroid — a simple blood test settles it. Unexplained weight loss deserves the same seriousness in the other direction. An endocrinology evaluation measures what calculators can only estimate.
This tool is informational. It estimates rather than measures, and it does not replace an assessment by a qualified clinician.
Frequently asked questions
What does BMR mean?
BMR stands for basal metabolic rate — the calories your body burns at complete rest to keep its basic functions running. It is the largest component of your daily energy expenditure.
Should I eat below my BMR to lose weight?
Usually no. Effective deficits sit between BMR and TDEE. Sustained intake below BMR is aggressive, hard on muscle and adherence, and best undertaken only with professional supervision.
Which BMR equation is most accurate?
Mifflin-St Jeor is the best-validated standard equation for most modern adults; Harris-Benedict remains a reasonable classic that reads slightly higher. Both are ±10% estimates — your real-world weight trend is the final calibration.
Why is my BMR so low?
Usually because the inputs say so: smaller, older or less muscular bodies burn less at rest. If a low result comes with symptoms — cold intolerance, fatigue, weight gain — ask your doctor about thyroid testing rather than dieting harder.
How can I increase my BMR?
Build muscle and keep it: resistance training plus adequate protein is the only lever with meaningful, lasting effect. Everything sold as a metabolism booster rounds to zero.
Is RMR the same as BMR?
Practically yes — RMR is measured under looser conditions and runs a few percent higher, but for planning purposes the numbers are interchangeable.
Numbers are a starting point — not a diagnosis
If your results raise questions, Acibadem specialists can review your situation properly: share your case and receive a free, no-obligation medical opinion from the relevant department.