🔥 BMR Calculator

What is BMR Calculator?

Basal metabolic rate is the number of calories your body burns just to keep essential functions running — breathing, circulating blood, repairing cells, and maintaining organ temperature — while you're completely at rest, not the calories used during a workout or even a walk to the kitchen. This calculator estimates that resting energy cost from your weight, height, and age, giving you a baseline figure that most diet and fitness planning starts from. Trainers, dietitians, and calorie-tracking apps all lean on a BMR number before adding activity on top of it, so knowing your own figure helps you make sense of any calorie target you're given elsewhere.

Mifflin-St Jeor Formula

Calculator King uses the Mifflin-St Jeor equation, widely regarded as more accurate for modern populations than the older Harris-Benedict formula it replaced:

Worked Example

Take a 30-year-old man weighing 70 kg and standing 170 cm tall:

That means his body burns roughly 1,672 calories a day even if he stayed in bed the entire time — before factoring in a single step of walking, a workout, or digestion.

How to Use This Calculator

1. Enter your current body weight in kilograms.
2. Enter your height in centimetres.
3. Enter your age in completed years.
4. Press Calculate to see your estimated resting calorie burn.

Things to Keep in Mind

BMR is only your resting number — it doesn't include the calories you burn walking, exercising, or even fidgeting through the day. For a complete daily calorie target you'll want to multiply this figure by an activity factor, which is exactly what our calorie calculator does. Muscle mass, thyroid function, genetics, and even sleep quality can shift your real BMR slightly above or below this formula-based estimate, so treat it as a well-informed starting point rather than an exact lab measurement.

Once you have your BMR, head over to the Calorie Calculator to turn it into a full daily calorie target based on how active you actually are.

Limitations to Keep in Mind

The Mifflin-St Jeor equation used here was derived from studies on a broad but still largely Western adult population, so it works best as a general estimate for healthy adults aged roughly 18-65 with an average body composition. It tends to be less accurate for people with very high or very low muscle mass, older adults whose metabolism has slowed with age, and people with diagnosed thyroid disorders — hypothyroidism or hyperthyroidism can shift real BMR up or down by 10-20%. It also isn't validated for children under 18, or for pregnant or breastfeeding women, whose energy needs follow separate trimester-based guidelines rather than a standard resting-metabolism formula. If you have a diagnosed metabolic or endocrine condition, or you're pregnant, treat this number as a rough reference only and ask your doctor or a registered dietitian for a figure adjusted to your specific situation.

Frequently Asked Questions

Q: Why does my BMR here differ from the number my gym app or trainer gave me?
A: Different apps use different formulas — Harris-Benedict, Mifflin-St Jeor, or the Katch-McArdle equation (which factors in body fat percentage) can each produce slightly different results for the same person. This calculator uses Mifflin-St Jeor because most nutrition research since the 1990s has found it more accurate for the general population than the older Harris-Benedict formula.

Q: Does BMR really decrease as I get older?
A: Yes, typically. Muscle mass tends to decline gradually after your 30s unless you actively strength train, and since muscle burns more calories at rest than fat tissue, resting metabolic rate usually drifts downward with age. This is one reason calorie needs in your 40s and 50s are often lower than in your 20s at the same weight.

Q: Is it safe to eat exactly at my BMR to lose weight faster?
A: Generally not recommended. Your BMR reflects only the calories needed for basic survival functions while lying still all day — eating at or below that level for extended periods can leave you fatigued, trigger muscle loss, and in some cases slow metabolism further. Most sustainable fat-loss plans keep intake above BMR but below total daily expenditure (TDEE).

Q: Can thyroid problems affect my actual BMR compared to this estimate?
A: Yes, significantly in some cases. An underactive thyroid (hypothyroidism) can lower real-world metabolic rate below what a formula predicts, while an overactive thyroid (hyperthyroidism) can raise it. If you have a diagnosed thyroid condition, or symptoms like unexplained weight change, fatigue, or temperature sensitivity, discuss your calorie needs with an endocrinologist rather than relying solely on this calculator.

Q: Should I use this number to make medical or dietary decisions on my own?
A: This calculator is meant for general education and fitness planning, not medical diagnosis. If you have a chronic condition, are underweight or significantly overweight, or are recovering from an eating disorder, please work with a doctor or registered dietitian to set an appropriate calorie target.

Factors That Influence Your Actual BMR

The formula gives a solid estimate, but several real-world factors can push your true resting metabolism above or below the calculated figure. Muscle mass is the single biggest lever — muscle tissue burns noticeably more calories at rest than fat tissue, so two people of identical weight, height, and age can have meaningfully different real BMRs depending on body composition. Genetics accounts for some baseline variation between individuals that no formula can capture, and thyroid hormone levels directly regulate metabolic rate, meaning conditions like hypothyroidism or hyperthyroidism can shift real BMR by 10-20% in either direction.

More Worked Examples

Seeing the formula applied to a few different profiles makes it easier to sanity-check your own result:

• 28-year-old woman, 58 kg, 160 cm: BMR = 447.593 + (9.247 × 58) + (3.098 × 160) − (4.330 × 28) = 447.593 + 536.3 + 495.7 − 121.2 ≈ 1,358 kcal/day
• 45-year-old man, 82 kg, 175 cm: BMR = 88.362 + (13.397 × 82) + (4.799 × 175) − (5.677 × 45) = 88.362 + 1,098.6 + 839.8 − 255.5 ≈ 1,771 kcal/day
• 60-year-old woman, 65 kg, 155 cm: BMR = 447.593 + (9.247 × 65) + (3.098 × 155) − (4.330 × 60) = 447.593 + 601.1 + 480.2 − 259.8 ≈ 1,269 kcal/day

Notice how the 60-year-old woman's BMR sits below the 28-year-old's despite a heavier body weight — the age deduction reflects the well-documented decline in resting metabolic rate that comes with ageing, largely driven by muscle loss.

📅 Last reviewed: July 2026 · Formulas verified against RBI/SEBI/IT Dept guidelines.