🔥 BMR Calculator (Basal Metabolic Rate)
Calculate the baseline calories your body consumes at complete resting state.
Basal metabolic rate, and turning it into a daily calorie target
Basal metabolic rate is what your body burns doing nothing at all: keeping your heart beating, your lungs working, your brain running and your temperature stable. For most people it accounts for 60% to 75% of total daily energy use, which is why the idea that exercise is the main lever on calorie burn is mostly wrong.
The Mifflin-St Jeor equation
Published in 1990, this is the formula most dietitians use because it outperformed the older Harris-Benedict equation against measured values in modern populations:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
A 35-year-old woman of 165 cm and 68 kg has a BMR of 680 + 1,031 − 175 − 161 = 1,375 calories a day. That is the floor, before she gets out of bed.
From BMR to total daily energy expenditure
Multiply BMR by an activity factor to get TDEE, the number that actually matters for eating:
| Activity level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little deliberate exercise |
| Lightly active | 1.375 | Light exercise 1–3 days a week |
| Moderately active | 1.55 | Moderate exercise 3–5 days a week |
| Very active | 1.725 | Hard exercise 6–7 days a week |
| Extremely active | 1.9 | Physical job, or twice-daily training |
The same woman, moderately active, has a TDEE of 1,375 × 1.55 = 2,131 calories. Sedentary, it would be 1,650. That 481-calorie gap is larger than most people's deliberate exercise, and it comes mostly from incidental movement rather than workouts.
The four components of daily burn
- BMR, 60–75%. Largely determined by lean body mass, which is why bigger and more muscular people burn more at rest.
- Thermic effect of food, about 10%. The energy used digesting what you eat. Protein costs the most to process, at 20–30% of its own calories, against 5–10% for carbohydrate and 0–3% for fat.
- Non-exercise activity thermogenesis, 15–30%. Walking, fidgeting, standing, housework. This is the most variable component between people and the one that quietly falls during a diet.
- Exercise, 0–30%. Deliberate training. Usually the smallest piece, and the one most overestimated.
Fitness trackers and gym machines routinely overestimate exercise calories, sometimes by 30% or more. If you are eating back the calories your watch says you burned, you may be eating back calories that were never spent.
Why metabolism slows on a diet
As you lose weight, BMR falls because there is less tissue to maintain. On top of that, the body reduces spontaneous movement and becomes slightly more efficient, an effect called adaptive thermogenesis, which can add another 5% to 15% reduction beyond what the weight loss alone predicts. This is the main reason a deficit that worked for two months stops working in month four. Recalculating TDEE every five kilograms keeps the target honest.
What actually raises BMR
Lean mass. A kilogram of muscle burns roughly 13 calories a day at rest against about 4.5 for a kilogram of fat, so the often-repeated claim that muscle burns 50 calories per pound is wildly overstated. Gaining five kilograms of muscle raises BMR by around 65 calories a day, which is real but modest. The bigger benefit of resistance training during weight loss is preserving the lean mass you already have.
A worked example
A 42-year-old man, 180 cm, 88 kg, lightly active. BMR = 880 + 1,125 − 210 + 5 = 1,800 calories. TDEE = 1,800 × 1.375 = 2,475. To lose about half a kilogram a week he needs roughly 1,975 calories a day. After losing 8 kg his BMR falls to 1,720 and TDEE to 2,365, so the same deficit now requires 1,865 calories.
This page explains published formulas and population-level ranges. It is general information, not medical advice, and it cannot account for your individual health. Talk to a doctor or a registered dietitian before changing how you eat, train or treat a condition.
Frequently Asked Questions (FAQs)
What is the difference between BMR and RMR?
BMR is measured under strict conditions: awake, fasted twelve hours, completely at rest, in a thermally neutral room. RMR, resting metabolic rate, is measured under less rigid conditions and comes out about 10% higher. In everyday use the terms are interchangeable and the formulas estimate something in between.
Should I eat below my BMR to lose weight faster?
It is not generally recommended. Eating below BMR tends to increase the proportion of lean tissue lost, worsens adherence, and makes it hard to get adequate protein and micronutrients. A deficit of 15% to 25% below TDEE, not below BMR, is the usual guidance.
Why is my BMR lower than my friend's at the same weight?
Lean mass, age and sex. Two people at 70 kg can differ by several kilograms of muscle, which changes BMR by 50 to 100 calories. Age reduces it by about 5 calories a year in the formula, and men average higher lean mass than women at the same weight.
How accurate is the Mifflin-St Jeor equation?
It predicts measured BMR within 10% for roughly 70% of people. That means a 1,600-calorie estimate could really be anywhere from 1,440 to 1,760. Use it as a starting point, then adjust based on what actually happens to your weight over two or three weeks.
Does eating more often speed up metabolism?
No. The thermic effect of food depends on how much and what you eat, not how it is divided across the day. Six small meals and three larger ones of the same composition produce the same total. Meal frequency is a question of appetite control and convenience.
Can I damage my metabolism with dieting?
Sustained severe restriction does reduce energy expenditure beyond what weight loss alone predicts, and some of that persists after the diet ends. It is a meaningful effect rather than permanent damage, and it is mitigated by moderate deficits, adequate protein and resistance training.