Free BMR Calculator
Compare adult resting-energy estimates from Mifflin–St Jeor and revised Harris–Benedict without activity multipliers. Use advanced options and copy or download your results. Browser-based and no signup required.
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How to use the bmr calculator
Compare adult resting-energy estimates from Mifflin–St Jeor and revised Harris–Benedict without activity multipliers. No signup required.
- Choose units and enter adult age, weight, height and the formula sex option.
- Select Mifflin–St Jeor or revised Harris–Benedict as the primary resting-energy equation.
- Compare the primary estimate, both equation results and the resting hourly equivalent.
- Read the distinction between resting energy and daily calorie needs, then copy or download your report.
Who uses a BMR estimate
Basal metabolic rate is the energy your body uses at complete rest to keep basic functions running. People planning meals, coaches setting a starting point for clients, and students learning about energy balance all use it as a baseline. It is the floor that daily activity is added on top of.
This calculator is built for adults aged 18 to 100. You can enter height and weight in metric or US units. It shows your selected estimate, the results from both equations side by side, and the same figure expressed in calories per hour.
Because it shows two equations at once, it is also a useful teaching tool. You can see how much the method alone changes the answer, which is a good reminder that any BMR figure is an estimate with a margin, not a lab measurement of your metabolism.
A worked example
Take a 30 year old man who weighs 80 kg and is 180 cm tall. Mifflin-St Jeor gives 10 x 80 + 6.25 x 180 - 5 x 30 + 5, which is 800 + 1,125 - 150 + 5 = 1,780 kcal per day. That is about 74 kcal per hour.
The revised Harris-Benedict equation for men is 88.362 + 13.397 x 80 + 4.799 x 180 - 5.677 x 30. That works out to about 1,854 kcal per day. For a 35 year old woman at 65 kg and 165 cm, Mifflin-St Jeor gives 650 + 1,031.25 - 175 - 161 = about 1,345 kcal, and revised Harris-Benedict gives about 1,408 kcal.
How the two equations differ
Mifflin-St Jeor uses 10 times weight in kilograms, plus 6.25 times height in centimeters, minus 5 times age. It then adds 5 for males or subtracts 161 for females. It is widely used in modern nutrition practice.
The revised Harris-Benedict equation uses different weights for each sex. For males it is 88.362 + 13.397W + 4.799H - 5.677A. For females it is 447.593 + 9.247W + 3.098H - 4.330A. It often lands somewhat higher than Mifflin-St Jeor for the same person, as the example shows.
Neither equation measures you directly. They are population estimates based on size, age, and sex, so a real person can differ by a meaningful amount. Muscle mass, health conditions, and some medications can all shift actual needs.
Common mistakes to avoid
Do not mix units. If you switch to US units, enter pounds and feet or inches, not kilograms. A wrong unit can change the answer by hundreds of calories.
Another common slip is entering an old weight or rounding age down by several years. Both inputs carry real weight in the formulas, and five years of age alone moves the Mifflin-St Jeor result by 25 kcal per day.
Do not treat BMR as total daily needs. Walking, work, and exercise all add energy on top of it. For weight goals, medical conditions, pregnancy, or sports nutrition, use the figure as general information and talk with a doctor or registered dietitian.
Useful tips and limitations
- No activity multiplier is applied here; use the Calorie & TDEE tool for a daily expenditure estimate.
- These equations predict resting energy; a measured basal metabolic rate requires controlled clinical conditions.
- Compare both equations and treat the range between them as a reasonable estimate rather than one exact number.
- Recalculate after a notable change in weight or a birthday, since both inputs move the result.
Common questions
How is this BMR calculator different from TDEE?
This page estimates energy at rest without an activity factor. TDEE also includes activity and other daily energy expenditure, so it is usually higher.
Which equations can I compare for basal energy?
You can compare Mifflin–St Jeor and the 1984 revised Harris–Benedict equations. These predict resting energy, often loosely called BMR, rather than measuring it.
Can the resting calorie result be used as my eating target?
Not by itself. An eating target depends on total daily expenditure, health and other needs. The tool is not intended for pregnancy, breastfeeding, under-18s or individualized medical nutrition.
Why do the two equations give different numbers?
They were fitted to different study groups with different coefficients, so the same inputs produce somewhat different estimates.
What does the per hour figure mean?
It is the daily BMR divided by 24, a simple way to see resting energy use over one hour.
Can teenagers use this calculator?
No. It accepts ages 18 to 100 because these equations are meant for adults.
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