BMR Calculator

The calculator needs four pieces of information — all easy to find or estimate accurately:

1. Age in years. Use your current age. The formula penalizes BMR by 5 calories per year of age, reflecting the gradual decline in resting metabolism most adults experience.
2. Sex. Select male or female. The Mifflin-St Jeor equation uses different intercepts (+5 for male, −161 for female) to reflect average differences in lean mass at the population level. If you have unusually high muscle mass for your sex, your true BMR may be a few percent above the calculator’s estimate.
3. Body weight in pounds. Use your current weight, not a goal weight. Step on a scale in the morning before eating for the most consistent reading. The calculator converts pounds to kilograms internally (1 lb = 0.453592 kg).
4. Height in feet and inches. Enter both fields. A 5′10″ person enters 5 and 10. The calculator combines these to centimeters using 1 ft = 30.48 cm and 1 in = 2.54 cm.

Your results show your BMR first — the calories your body burns just keeping you alive at rest — followed by four TDEE estimates at progressively higher activity levels. Pick the multiplier that matches your average week, not your most active week. Most people overestimate their activity level, which is the single biggest reason calorie targets fail. If you sit for work and exercise 3 times per week, you’re probably "Light," not "Moderate."

For weight loss, subtract 250–500 calories from your matching TDEE. For weight gain, add the same amount. Recalculate every 10–15 pounds of weight change — as you get smaller (or larger), your BMR moves with you, and a target that was correct three months ago may be off by 100–200 calories today.

Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to keep you alive. Breathing, pumping blood, replacing cells, regulating body temperature, processing waste — even on a day where you do absolutely nothing, your body is running expensive background processes that account for the bulk of your calorie burn.

For most adults, BMR represents roughly 60–70% of total daily energy expenditure. The rest comes from two sources: the calories you burn moving around (everything from formal exercise to fidgeting, collectively called the activity thermogenesis) and the small overhead your body pays to digest food itself (the thermic effect of food, typically 8–15% of calories consumed). When you multiply BMR by an activity multiplier, you get an estimate of your total daily energy expenditure (TDEE) — the calories you actually burn in a real day.

Several factors push BMR up or down. Body size matters most: a 200-pound person burns more at rest than a 130-pound person, simply because more tissue requires more energy to maintain. Lean muscle mass burns roughly three times the calories that fat tissue does per pound, which is why two people of identical weight can have meaningfully different BMRs depending on body composition. Age slowly drops BMR — roughly 2–3% per decade after 30, mostly because of gradual muscle loss rather than metabolism “slowing” on its own. Sex matters too: men typically have higher BMRs than women of equal weight and height because they tend to carry more lean mass. Hormones (especially thyroid output), genetics, ambient temperature, and certain medications can all shift BMR up or down by 5–15%.

BMR is the foundation for almost every nutrition strategy. Whether your goal is weight loss, muscle gain, or maintenance, the calorie target you choose is built on top of it. A 500-calorie daily deficit produces roughly one pound of fat loss per week (one pound of fat ~= 3,500 calories), which is the standard sustainable rate. A 250–500 calorie surplus paired with resistance training is the typical recommendation for adding lean mass.

Disclaimer: This calculator provides educational estimates only. It is not a substitute for medical or nutritional advice. People with thyroid conditions, diabetes, eating disorders, or who are pregnant or nursing should work with a registered dietitian or physician before adjusting calorie intake.

The calculator uses the Mifflin-St Jeor equation, published by Mifflin and colleagues in 1990 in the American Journal of Clinical Nutrition. A 2005 review by the Academy of Nutrition and Dietetics found it more accurate than the older Harris-Benedict equation (1919) for modern populations, with average error of about 5% for non-obese adults.

Mifflin-St Jeor equations:

• Male: BMR = 10w + 6.25h − 5a + 5
• Female: BMR = 10w + 6.25h − 5a − 161

Once BMR is known, daily calorie needs (TDEE) are estimated by multiplying BMR by an activity factor:

• Sedentary (desk job, no exercise): BMR × 1.20
• Light (light exercise 1–3 days/week): BMR × 1.375
• Moderate (moderate exercise 3–5 days/week): BMR × 1.55
• Very active (hard exercise 6–7 days/week): BMR × 1.725

A note on accuracy: the Mifflin-St Jeor equation was developed and validated on a healthy adult population. For very lean athletes (high muscle mass) it tends to underestimate BMR by a few percent; for individuals with significant obesity it can overestimate. Indirect calorimetry — measuring oxygen consumption in a metabolic chamber — is the gold standard if precision is critical, but for everyday nutrition planning the formula is plenty accurate.

Example 1 — Sedentary office worker (female). 35 years old, 160 lbs, 5′6″.

• Weight: 160 × 0.453592 = 72.57 kg
• Height: 5×30.48 + 6×2.54 = 167.64 cm
• BMR = 10×72.57 + 6.25×167.64 − 5×35 − 161
• BMR = 725.75 + 1,047.75 − 175 − 161 = 1,437 calories/day
• Sedentary TDEE = 1,437 × 1.20 = 1,724 calories/day

To lose ~1 lb/week she’d eat around 1,224 calories/day (a 500-calorie deficit) — though most clinicians would push her toward 1,400 calories combined with light walking, since aggressive deficits below 1,200 are hard to sustain and can shed lean mass.

Example 2 — Moderately active man. 40 years old, 200 lbs, 6′0″.

• Weight: 200 × 0.453592 = 90.72 kg
• Height: 6×30.48 = 182.88 cm
• BMR = 10×90.72 + 6.25×182.88 − 5×40 + 5
• BMR = 907.18 + 1,143.00 − 200 + 5 = 1,855 calories/day
• Moderate TDEE = 1,855 × 1.55 = 2,875 calories/day

If he’s trying to recomp (lose fat while maintaining muscle), eating at maintenance and adding resistance training is a reasonable approach. For a 1 lb/week cut, he’d target ~2,375 calories/day with adequate protein (around 0.8–1.0 g per pound of bodyweight).

Example 3 — Endurance athlete (female). 28 years old, 140 lbs, 5′5″.

• Weight: 140 × 0.453592 = 63.50 kg
• Height: 5×30.48 + 5×2.54 = 165.10 cm
• BMR = 10×63.50 + 6.25×165.10 − 5×28 − 161
• BMR = 635.00 + 1,031.88 − 140 − 161 = 1,366 calories/day
• Very active TDEE = 1,366 × 1.725 = 2,356 calories/day

For a competitive endurance athlete training daily, even 2,356 may underestimate true needs — high-volume training can push activity factors above 1.9 in some cases. If she finds she’s losing weight on 2,400 calories without trying, that’s the signal to step intake up by 200–300 calories rather than push her training harder.