Your Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic life functions at complete rest — breathing, circulation, organ function, and cell production — with zero physical activity. It's the foundation of every calorie-based diet plan, and understanding it prevents the most common mistake in weight management: not eating enough.
What BMR Measures (and Doesn't)
BMR is measured under strict conditions: fasting state, complete rest, comfortable temperature, awake. In practice, your actual resting calorie burn (Resting Metabolic Rate, RMR) is slightly higher (5–10%) because you're rarely in a perfectly basal state. For practical use, BMR and RMR are interchangeable; the difference is less important than the activity multiplier applied after.
BMR accounts for 60–70% of your total daily calorie expenditure. Physical activity adds 20–30%; digesting food (thermic effect of food) adds about 10%. This is why dramatic calorie restriction often fails: cutting calories too far below BMR slows metabolism and causes muscle loss.
The Mifflin-St Jeor Formula (Most Accurate)
Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Worked Example — Man, 35 Years, 82 kg, 178 cm
- (10 × 82) = 820
- (6.25 × 178) = 1,112.5
- (5 × 35) = 175
- BMR = 820 + 1,112.5 − 175 + 5 = 1,762.5 kcal/day
Worked Example — Woman, 28 Years, 63 kg, 165 cm
- (10 × 63) = 630
- (6.25 × 165) = 1,031.25
- (5 × 28) = 140
- BMR = 630 + 1,031.25 − 140 − 161 = 1,360.25 kcal/day
BMR by Age and Weight — Reference Table (Women)
| Age | 55 kg | 65 kg | 75 kg | 85 kg |
|---|---|---|---|---|
| 25 | 1,302 | 1,402 | 1,502 | 1,602 |
| 35 | 1,252 | 1,352 | 1,452 | 1,552 |
| 45 | 1,202 | 1,302 | 1,402 | 1,502 |
| 55 | 1,152 | 1,252 | 1,352 | 1,452 |
Approximate values for height 165 cm. For other heights, adjust by ±6.25 kcal per cm from 165.
tdee-adding-activity">From BMR to TDEE — Adding Activity
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little/no exercise | × 1.2 |
| Lightly active | Exercise 1–3 days/week | × 1.375 |
| Moderately active | Exercise 3–5 days/week | × 1.55 |
| Very active | Hard exercise 6–7 days/week | × 1.725 |
| Extra active | Physical job + heavy training | × 1.9 |
Example: BMR 1,762 kcal × 1.55 (moderately active) = TDEE 2,731 kcal/day. To lose 0.5 kg/week: eat 2,731 − 550 = 2,181 kcal/day.
Why BMR Changes Over Time
BMR decreases with age (roughly 2% per decade after 25) due to muscle loss. Building and maintaining muscle mass is the most effective way to sustain a higher BMR as you age — resistance training 2–3× per week is more effective at preserving metabolic rate than cardio. Each kilogram of muscle burns approximately 13 kcal/day at rest; fat burns around 4.5 kcal/kg/day.