BMR Calculator: Complete Guide to Basal Metabolic Rate
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep you alive. It accounts for 60–75% of your total daily energy expenditure, making it the single most important number for any nutrition plan.
What Is BMR?
BMR represents the energy your body needs for essential functions: breathing, circulating blood, regulating temperature, maintaining organ function, and keeping your brain running. Even if you slept all day, you'd still burn your BMR in calories.
Three BMR Formulas Explained
Our calculator compares three scientifically validated formulas side by side:
1. Mifflin-St Jeor (Most Recommended)
Published in 1990, this is considered the most accurate formula for the general population:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
2. Harris-Benedict (Classic)
The original formula from 1919, revised in 1984. It tends to slightly overestimate BMR by 5–10%:
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
3. Katch-McArdle (Best for Athletes)
This formula uses lean body mass instead of total weight, making it the most accurate if you know your body fat percentage:
BMR = 370 + 21.6 × lean body mass(kg)
Which Formula Should You Use?
| Situation | Recommended Formula | Why |
|---|---|---|
| General use | Mifflin-St Jeor | Most validated for general population |
| Clinical settings | Harris-Benedict | Still used in many hospitals |
| Know your body fat % | Katch-McArdle | Accounts for muscle mass |
| Not sure | Mifflin-St Jeor | Best all-around choice |
From BMR to TDEE
BMR alone doesn't tell you how many calories to eat. You need to multiply it by an activity factor:
| Activity Level | Multiplier | Example (BMR 1500) |
|---|---|---|
| Sedentary (desk job) | ×1.2 | 1,800 kcal |
| Light (1–3 workouts/week) | ×1.375 | 2,063 kcal |
| Moderate (3–5 workouts/week) | ×1.55 | 2,325 kcal |
| Active (6–7 workouts/week) | ×1.725 | 2,588 kcal |
| Athlete (daily intense training) | ×1.9 | 2,850 kcal |
How to Use BMR for Your Goals
Fat Loss
- Eat 300–500 kcal below TDEE (not below BMR)
- Never eat below BMR for extended periods
- Prioritize protein (1.6–2.2 g/kg)
Muscle Gain
- Eat 200–400 kcal above TDEE
- Focus on progressive overload in training
- Track weight trend over 2–3 weeks
Maintenance
- Eat at TDEE
- Adjust based on real-world results after 2 weeks
Factors That Affect BMR
You can't change: Age, genetics, sex, height You CAN change: Muscle mass (most impactful), sleep quality, stress levels, diet history
Muscle burns 6–10 calories per pound at rest, while fat burns only 2–3. Building 10 lbs of muscle adds 60–100 calories to your daily BMR.
Calculate your calorie deficit → Plan your macros →
Common BMR Mistakes
- Eating below BMR — Causes muscle loss and metabolic adaptation
- Using BMR as your calorie target — BMR is only your resting burn; you need TDEE
- Ignoring activity changes — TDEE changes when your activity changes
- Trusting formulas blindly — Formulas estimate; your body is the truth