BMR calculator

Basal metabolic rate (BMR) is the energy your body needs at rest to keep vital systems running. This calculator estimates BMR with the Mifflin-St Jeor equation so you can see your resting baseline before activity is added.

BMR versus TDEE: know the difference

BMR is your resting energy burn—roughly what you would use lying still all day. Total daily energy expenditure (TDEE) adds the cost of walking, working, training, fidgeting, and digesting food. Your practical eating target for weight change is almost always based on TDEE, not BMR alone. Eating far below BMR for long stretches is usually unnecessary and hard to sustain for active adults.

People often confuse the two and set calorie targets too low. A useful sequence is: estimate BMR, multiply by a realistic activity factor to get TDEE, then create a modest deficit or surplus from that higher number. FreeNutri's BMR calculator is free and needs no account, so you can check the resting piece of the puzzle in seconds.

How Mifflin-St Jeor works

Mifflin-St Jeor estimates BMR from weight, height, age, and sex. In metric form: for men, BMR ≈ 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women, the same formula ends with −161 instead of +5. Convert pounds to kilograms by dividing by 2.2, and inches to centimeters by multiplying by 2.54.

Example: a 35-year-old woman at 5'5" (165 cm) and 160 lb (about 72.7 kg) lands near 1,420 kcal for BMR. That is not her daily food target. If she is lightly active, multiplying by about 1.375 suggests a TDEE near 1,950 kcal, which is a more realistic planning baseline.

What raises or lowers resting burn

Larger bodies and more lean mass generally mean higher BMR. Aging tends to lower average BMR partly because muscle mass often declines when people move less. Crash dieting can also reduce daily burn through lower body weight, less spontaneous movement, and adaptive changes. Strength training and adequate protein help preserve the lean tissue that supports a healthier metabolism.

Sleep, stress, and medications can influence energy use and appetite even when the formula stays the same. If your lifestyle changes—new job on your feet, new training block, major weight change—recalculate rather than clinging to an old number.

Using BMR without under-eating

Think of BMR as the engine idling figure, not the full trip budget. Set meal plans from TDEE, keep protein high enough to protect muscle, and include carbohydrates around training if performance matters to you. Extreme deficits that sit near or under BMR for weeks often backfire through fatigue, poor workouts, and rebound eating.

If hunger is constant and workouts collapse, raise calories even if the spreadsheet looks “perfect.” Sustainable progress usually comes from a moderate gap between intake and TDEE plus habits you can repeat on busy weeks.

Pair BMR with real-world tracking

After you have BMR and an activity-based TDEE, watch a two-to-four-week weight average. Flat weight during a planned deficit may mean true burn is lower than estimated, portions are higher than logged, or both. Adjust by 100–200 calories or add steps before making dramatic cuts.

Keep notes on energy, sleep, and training quality. Those soft signals often warn you earlier than the scale that intake is too aggressive. Recheck BMR when weight changes meaningfully so your resting baseline stays roughly current.

From BMR to a week you can live with

Once you know estimated BMR and TDEE, sketch a simple week: similar breakfasts, protein-centered lunches, and dinners you can cook in under thirty minutes. Put harder training on days when you can eat enough carbohydrates to perform. Leave buffer calories for a social meal so the plan does not shatter on Friday night. The math only works when the schedule matches your real calendar.

If you like spreadsheets, log for two weeks and compare predicted change with actual average weight. If reality diverges, trust the trend and update intake rather than arguing with the equation. BMR knowledge is useful; lived feedback is decisive. Recalculate after major weight change and keep protein steady while you experiment with carbs and fats. Athletes returning from a layoff often notice that old calorie targets feel high until training volume returns. Recalculate BMR and activity together after breaks longer than a couple of weeks so your plan matches your current routine, not last season’s peak. Office workers who start a walking habit should bump activity assumptions before cutting food again. Sometimes the missing piece is movement, not another hundred calories removed from lunch.