BMR Calculator
Estimate your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor and Harris-Benedict (revised) equations. Enter age, sex, height, and weight to see your estimated resting daily calorie burn.
How It's Calculated
Formula
\text{Mifflin-St Jeor (male)} = 10w + 6.25h - 5a + 5
\text{Mifflin-St Jeor (female)} = 10w + 6.25h - 5a - 161
\text{Harris-Benedict, revised 1984 (male)} = 88.362 + 13.397w + 4.799h - 5.677a
\text{Harris-Benedict, revised 1984 (female)} = 447.593 + 9.247w + 3.098h - 4.330a
\text{where } w = \text{weight (kg)},\ h = \text{height (cm)},\ a = \text{age (years)}BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep basic functions running — breathing, circulation, cell repair. It is an estimate produced by a published predictive equation, not a measured value from a metabolic testing device (indirect calorimetry). This is an estimate for general informational and educational purposes, based on a published formula — it is not a medical diagnosis, and it is not a substitute for individualized advice from a qualified healthcare provider. This calculator computes two such equations side by side. Mifflin-St Jeor (1990) is the primary, recommended formula: subsequent validation research has generally found it more accurate for the modern general population than the older Harris-Benedict equation. Harris-Benedict, using the REVISED 1984 constants from Roza and Shizgal (not the original 1919 version, which uses different, less accurate coefficients), is shown as a secondary estimate for comparison. Both take age, sex, height, and weight as inputs — unlike BMI, sex is a real variable in both formulas here, changing the constant term applied. Neither formula accounts for body composition (muscle vs. fat mass) directly, so results are population averages, not individualized measurements. BMR is also not the same as your total daily calorie needs: it excludes the calories burned through daily activity, exercise, and digestion. That full picture is Total Daily Energy Expenditure (TDEE), calculated by applying an activity multiplier on top of BMR.
Worked Examples
Male, 30 years old, 80 kg, 180 cm
- Mifflin-St Jeor: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 800 + 1125 − 150 + 5 = 1780 kcal/day
- Harris-Benedict (revised 1984): 88.362 + 13.397 × 80 + 4.799 × 180 − 5.677 × 30 = 88.362 + 1071.76 + 863.82 − 170.31 = 1853.63 kcal/day
- The two estimates differ by about 74 kcal/day; the Mifflin-St Jeor figure (1780) is the recommended one to use.
Female, 25 years old, 60 kg, 165 cm
- Mifflin-St Jeor: 10 × 60 + 6.25 × 165 − 5 × 25 − 161 = 600 + 1031.25 − 125 − 161 = 1345.25 kcal/day
- Harris-Benedict (revised 1984): 447.593 + 9.247 × 60 + 3.098 × 165 − 4.330 × 25 = 447.593 + 554.82 + 511.17 − 108.25 = 1405.33 kcal/day
- The two estimates differ by about 60 kcal/day; the Mifflin-St Jeor figure (1345) is the recommended one to use.
Frequently Asked Questions
Why does this calculator show two different formulas?
Mifflin-St Jeor (1990) and Harris-Benedict (revised 1984) are both widely-cited published predictive equations for resting energy expenditure, and calculators commonly show both so you can compare them. They use different constants and will not produce identical results for the same inputs — that difference is expected, not an error.
Which BMR estimate is more accurate — which should I use?
Mifflin-St Jeor is generally considered the more accurate equation for the modern general population, per validation studies conducted since its publication (e.g. Frankenfield et al., 2005). This calculator marks it as the primary result for that reason. The Harris-Benedict (revised) figure is shown as a secondary reference point, not an equally-recommended alternative.
Why does sex change the result here, when it doesn't for BMI?
BMI is a simple ratio of weight to height squared and applies the same formula regardless of sex. BMR estimates resting energy expenditure, which differs by sex due to average differences in body composition (e.g. muscle mass) — both Mifflin-St Jeor and Harris-Benedict were derived with separate constants for male and female specifically to capture that difference. This is a deliberate feature of the BMR formulas, not an inconsistency with BMI.
Is BMR the same as how many calories I can eat per day?
No. BMR is only the calories your body burns at complete rest — it does not include calories burned through walking, exercise, digestion, or any other daily activity. Your total daily calorie burn is called TDEE (Total Daily Energy Expenditure), calculated by multiplying BMR by an activity-level factor. Use a TDEE calculator, not this BMR figure alone, to estimate calorie needs for weight maintenance, loss, or gain.
What ages and inputs does this calculator support?
Age must be between 15 and 100 years — both formulas were derived from adult populations and are not validated outside that range. Height and weight must be positive numbers; you can enter height in centimeters or total inches, and weight in kilograms or pounds.