BMR Calculator - Compare Mifflin-St Jeor, Harris-Benedict & Katch-McArdle
You're 35, 5'9", and 170 lb, wondering how many calories your body burns at complete rest before workouts or commuting. Mifflin-St Jeor puts your BMR near 1,700 kcal/day—compare it to Harris-Benedict and Katch-McArdle below, then layer activity for TDEE if you're planning meals.
BMR Formula Comparison
Calorie Deficit Timeline
Estimated weeks to lose 10 lbs at different deficit rates (using Mifflin-St Jeor BMR):
Methodology and limitations
Last reviewed:
Methodology
Calculates BMR using Mifflin-St Jeor, Harris-Benedict, and optionally Katch-McArdle (if body fat provided) formulas. Projects calorie deficit timelines at 0.5% and 1% weekly body weight loss rates.
Limitations
BMR formulas are population averages and do not account for individual metabolic variance, medical conditions, or adaptive thermogenesis during prolonged dieting.
Official sources
How BMR Is Calculated and Compared
You're 35, 5'9", and 170 lb, wondering how many calories your body burns at complete rest before workouts or commuting. Mifflin-St Jeor puts your BMR near 1,700 kcal/day—compare it to Harris-Benedict and Katch-McArdle below, then layer activity for TDEE if you're planning meals.
Method used
The calculator estimates BMR using Mifflin-St Jeor, Harris-Benedict, and optionally Katch-McArdle formulas. It compares results side by side and projects calorie deficit timelines for weight loss.
Mifflin-St Jeor: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (male) or −161 (female); Harris-Benedict uses different constants; Katch-McArdle uses lean mass
Practical example
A 35-year-old male, 5'9", 170 lbs has a Mifflin-St Jeor BMR near 1,696 kcal/day. A 40-year-old female, 5'4", 155 lbs on her feet all day can compare BMR to TDEE. With a 500 kcal daily deficit, 10 lbs lost takes about 10 weeks.
- Age: 35 years
- Sex: male, height: 5'9", weight: 170 lbs
- Optional: body fat percentage for Katch-McArdle
The result compares BMR across formulas, shows deficit projections for 0.5% and 1% weekly body weight loss, and includes timeline estimates.
Assumptions
- BMR formulas are population-based estimates.
- Deficit projections use 3,500 kcal per pound approximation.
- 1,200 kcal floor is enforced on deficit targets.
What this includes
- Three BMR formulas compared, optional Katch-McArdle with body fat, deficit timelines, goal weight projections.
What this excludes
- Activity multipliers (see TDEE), metabolic adaptation, medical conditions, pregnancy, athlete-specific needs, clinical diet plans.
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Frequently Asked Questions
What is BMR?
BMR, or basal metabolic rate, is the estimated number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, and cell maintenance. It does not include walking, workouts, or digestion above basal needs. Compare Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle here for context. Treat BMR as an educational baseline, not a medical calorie order.
How is BMR different from TDEE?
BMR is resting energy expenditure under standardized assumptions. TDEE multiplies BMR by an activity factor to estimate total daily calories burned including exercise and non-exercise movement. Meal planning usually starts from TDEE, not raw BMR, unless a clinician directs otherwise. Use BMR to understand the resting floor, then layer activity for realistic daily targets.
Which BMR formula is most accurate?
Mifflin-St Jeor is often preferred for general adult populations in modern practice. Katch-McArdle can fit athletes better when body fat is known because it uses lean mass. Harris-Benedict is an older alternative still shown for comparison. No equation matches every person—validate with weight trends over weeks and seek clinical advice for medical nutrition needs.
Can I lose weight by eating only my BMR?
Eating at BMR while remaining active creates a deficit relative to TDEE, but very low intake can impair training, hormones, and adherence. A moderate deficit from estimated TDEE is usually more sustainable than living at true basal calories. This is educational guidance only; restrictive diets with medical conditions need professional supervision.
Why do BMR formulas differ by gender?
Population equations include sex-specific constants because average body composition differs: men typically carry more lean mass at a given height and weight. The adjustment is statistical, not a judgment about individuals. Transgender and hormone-therapy contexts may need clinician-guided approaches beyond binary formula defaults—ask a knowledgeable provider when standard inputs do not fit.