BMR Calculator

What is a BMR calculator?

A BMR calculator estimates your basal metabolic rate — the number of calories your body burns at complete rest over 24 hours just to stay alive. That resting energy powers breathing, circulation, brain activity, organ function and keeping you warm, before any movement is added. The tool above turns four simple inputs — weight, height, age and sex — into a single figure in kilocalories per day (kcal/day).

Your BMR is the foundation of almost every calorie plan. It is the largest single slice of daily energy use for most people, so knowing it gives you a realistic baseline before you layer on activity, set a goal, or decide how much to eat to lose, maintain or gain weight.

How does the BMR calculator work?

This calculator uses the Mifflin-St Jeor equation, the formula most dietitians and researchers regard as the most accurate for the general population. It takes a slightly different constant for men and women:

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

The terms are straightforward:

• weight(kg) — body mass in kilograms.
• height(cm) — standing height in centimetres.
• age — age in whole years.
• sex — sets the final constant (+5 for men, −161 for women), reflecting the fact that men typically carry more lean mass.

If you enter imperial units, the tool converts first: pounds are multiplied by 0.45359237 to get kilograms, and inches are multiplied by 2.54 to get centimetres. The result is then rounded to the nearest whole kcal/day.

Examples

Here are fully worked calculations that match the tool’s output exactly.

Example 1 — Man, 70 kg, 175 cm, 30 years

• 10 × 70 = 700
• 6.25 × 175 = 1093.75
• −5 × 30 = −150
• Men constant: +5
• Total: 700 + 1093.75 − 150 + 5 = 1648.75 → about 1649 kcal/day

Example 2 — Woman, 70 kg, 175 cm, 30 years (same stats)

• 700 + 1093.75 − 150 − 161 = 1482.75 → about 1483 kcal/day

The only difference from Example 1 is the constant (−161 instead of +5), which is why the woman’s BMR is 166 kcal lower for identical weight, height and age.

Example 3 — Woman, 60 kg, 165 cm, 35 years

• 10 × 60 = 600
• 6.25 × 165 = 1031.25
• −5 × 35 = −175
• Women constant: −161
• Total: 600 + 1031.25 − 175 − 161 = 1295.25 → about 1295 kcal/day

Example 4 — Man, 154 lb, 70 in, 30 years (imperial)

• Convert: 154 × 0.45359237 = 69.85 kg; 70 × 2.54 = 177.8 cm
• 10 × 69.85 = 698.5
• 6.25 × 177.8 = 1111.25
• −5 × 30 = −150, men constant +5
• Total: 698.5 + 1111.25 − 150 + 5 = 1664.75 → about 1665 kcal/day

BMR reference table (Mifflin-St Jeor)

The table below shows BMR in kcal/day calculated straight from the formula, at a fixed height to isolate the effect of weight, age and sex. Men are shown at 175 cm and women at 165 cm.

Profile	60 kg	70 kg	80 kg
Man, 175 cm, age 30	1549	1649	1749
Man, 175 cm, age 50	1449	1549	1649
Woman, 165 cm, age 30	1320	1420	1520
Woman, 165 cm, age 50	1220	1320	1420

Two patterns stand out: BMR rises by roughly 100 kcal for every extra 10 kg of body weight, and it drops by about 100 kcal across 20 years of ageing (5 kcal per year). Use the closest row as a quick check, or enter your exact figures in the tool for a precise number.

Common uses

A BMR figure is useful well beyond curiosity:

• Set a calorie target. Multiply BMR by an activity factor (about 1.2 sedentary up to 1.9 very active) to estimate your total daily energy expenditure (TDEE), the maintenance calories that keep weight stable.
• Plan weight loss or gain. Subtract or add calories from TDEE — not from BMR — to create a sensible deficit or surplus.
• Track changes over time. Re-run it after weight changes to see how your resting burn shifts.
• Compare formulas. Check the Mifflin-St Jeor result against other estimates your fitness app may show.

Tips and common mistakes

• Do not eat at your BMR. BMR is your at-rest need only; an active person who eats at BMR is usually in a large, unintended deficit. Base intake on TDEE instead.
• BMR is not the same as TDEE. TDEE includes movement, exercise and digestion; it is always higher than BMR.
• Use consistent, current numbers. Enter your present weight and height; outdated figures give an outdated BMR.
• Round sensibly. A BMR of 1648.75 displays as 1649 — treat the figure as an estimate, not a precise calorie ration.
• Sex changes the constant, not the method. Switching from male to female lowers the result by 166 kcal for the same body, because the formula swaps +5 for −161.

Limitations and notes

The Mifflin-St Jeor equation is accurate for most adults, but it is still a population estimate, not a measurement of your individual metabolism. It does not account for body composition, so it can over- or under-estimate BMR for very muscular, very lean, or higher-body-fat individuals — two people of the same weight, height, age and sex receive the identical figure even if their muscle mass differs. It is also validated for adults; children, pregnant or breastfeeding people, and those with thyroid or other metabolic conditions may have very different needs. Real-world energy use also varies with genetics, hormones, temperature and recent dieting.

Health disclaimer: This BMR calculator is provided for general information and education only. It is not medical, nutritional or fitness advice, and it is not a substitute for professional assessment. Before making decisions about your diet, calorie intake or health, consult a qualified healthcare professional.

For more health self-checks, try the BMI calculator to gauge weight for height, the body fat calculator to estimate body composition, or the water intake calculator for daily hydration, and browse the full health & medical category for more tools.