BMR Calculator
Estimate your basal metabolic rate at rest. Provide body fat % to use Katch–McArdle, or leave it blank to use Mifflin–St Jeor.
What BMR tells you—and how to use it
Basal metabolic rate (BMR) estimates how much energy your body uses at rest in a neutral, fasted state. It reflects the work of your heart, lungs, brain, liver, kidneys, and all the cellular housekeeping that keeps you alive. Even on a day without workouts, your body quietly burns a large share of your daily calories just by maintaining basic function. Knowing this baseline helps you plan intake with more confidence.
How this calculator estimates BMR
- Mifflin–St Jeor: A modern, widely used equation based on age, sex, height, and weight.
- Katch–McArdle: If you provide body fat %, we calculate BMR from lean body mass. This can be helpful for people who are very lean, very muscular, or carrying more fat than average.
- Activity table: We multiply your BMR by standard activity factors to showestimated daily calorie needs for different routines—from mostly seated days to intense training or physically demanding work.
What affects BMR
- Body size and composition: More mass burns more energy; lean mass is especially metabolically active.
- Age and sex: BMR tends to decline with age and differs on average between males and females.
- Hormones and health: Thyroid status, fever, recovery from injury, and certain medications can shift energy use.
- Recent intake and sleep: Severe dieting, poor sleep, and large changes in activity can temporarily affect needs.
From BMR to daily calories
BMR alone isn’t a daily target; it’s the baseline. Total daily energy expenditure (TDEE) adds everything you do on top of that—walking, training, chores, fidgeting, digestion. The activity table below your result provides a quick ladder of possibilities. If you’re adjusting body weight, choose a realistic activity row and then create a small, sustainable deficit or surplus around that value.
Practical tips
- Track a weekly average of body weight to smooth daily water swings.
- Keep steps and sleep relatively consistent while you test a calorie target.
- If progress stalls for 2–3 weeks, nudge intake by ~100–150 calories/day and reassess.
- Recalculate when weight changes meaningfully (about ±2–3%) or your routine shifts.
Getting a good body fat estimate (optional)
If you use the body fat % input, measure in a consistent way. Tape measurements (waist, neck, hip for women) taken in a relaxed posture, or a well-calibrated device, can improve the Katch–McArdle estimate. Professional methods like DEXA can offer more precision but aren’t necessary for everyday planning.
Limitations
Equations produce estimates, not lab measurements. Individual variation, medical conditions, and day-to-day behavior can shift energy needs. Use the numbers as a starting point, observe your results, and adjust. If you have a medical condition, consult a qualified professional before making large changes to training or diet.
Educational use only; not a medical diagnosis.
BMR Calculator — FAQ
What is BMR?
Basal Metabolic Rate (BMR) is the energy your body needs at rest to power vital functions like breathing, circulation, and cell maintenance. It’s the foundation for estimating total daily calories.
Which BMR formula do you use?
This calculator uses Mifflin–St Jeor, a modern formula that predicts BMR from age, sex, height, and weight. Research shows it performs well for the general population compared to older equations like Harris–Benedict.
What’s the difference between BMR and TDEE?
BMR is your resting baseline. TDEE (Total Daily Energy Expenditure) scales BMR by an activity multiplier to account for steps, chores, training, and job demands.
Does muscle mass affect BMR?
Yes. More lean mass generally raises BMR. Equations estimate this indirectly via weight, height, sex, and age; very muscular or very petite individuals may see small offsets versus the estimate.
How accurate is BMR?
BMR formulas provide a practical starting point. Real needs can vary with genetics, hormones, and body composition. Track progress for 2–3 weeks and adjust as needed.
How often should I recalculate BMR?
Recalculate when your weight changes meaningfully (≈2–3%), when activity level shifts, or every few months during a program.
Should I include exercise in BMR?
No. BMR excludes exercise by definition. Add an activity factor after BMR to estimate TDEE.
Use cases & examples
Example 1 — Male, 35, 5′10″ (70 in), 180 lb, Moderately Active
Convert units: 180 lb → 81.6 kg; 70 in → 177.8 cm. Mifflin–St Jeor (male): 10×kg + 6.25×cm − 5×age + 5.
- BMR ≈ 1,758 kcal/day
- TDEE (Moderate, ×1.55) ≈ 2,724 kcal/day
For gradual fat loss, many aim for ~250–500 kcal below TDEE; for slow gain, ~150–300 kcal above TDEE.
Example 2 — Female, 30, 5′5″ (65 in), 150 lb, Lightly Active
Convert units: 150 lb → 68.0 kg; 65 in → 165.1 cm. Mifflin–St Jeor (female): 10×kg + 6.25×cm − 5×age − 161.
- BMR ≈ 1,401 kcal/day
- TDEE (Light, ×1.375) ≈ 1,927 kcal/day
Choose a sustainable pace. Smaller adjustments are easier to maintain and review after 2–3 weeks.
Example 3 — Desk job vs. very active
A BMR of 1,600 kcal/day yields very different TDEEs across activity:
- Sedentary (×1.2): 1,920 kcal/day
- Moderate (×1.55): 2,480 kcal/day
- Very Active (×1.9): 3,040 kcal/day
Activity level is often the biggest driver of daily calorie needs after BMR.