Quick answer
Basal metabolic rate (BMR) is the energy your body uses at complete rest in a day. This calculator estimates it with the Mifflin–St Jeor equation and shows the revised Harris–Benedict result alongside for comparison.
BMR is not the calories you need in a day, because it leaves out movement. To estimate daily needs, multiply it by an activity factor, which the TDEE and calorie calculators on this site do.
Related tools: BMI Calculator: Find your Body Mass Index (BMI) and weight status. TDEE Calculator: Total daily energy expenditure from BMR and activity level. Calorie Calculator: Daily calories to maintain, lose or gain weight.
How to use the BMR Calculator
- Choose units: Metric (kg, cm) and Imperial (lb, in).
- Choose sex: Male and Female.
- Enter weight (kg, or lb) (between 20 and 500).
- Enter height (cm, or in) (between 50 and 250).
- Enter age (years) (a whole number, between 15 and 100).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Units | Choose one: Metric (kg, cm); Imperial (lb, in) | Starts at Metric (kg, cm) |
| Sex | Choose one: Male; Female | Starts at Male |
| Weight (kg, or lb) | A number | ≥ 20, ≤ 500 |
| Height (cm, or in) | A number | ≥ 50, ≤ 250 |
| Age | A whole number, in years | ≥ 15, ≤ 100 |
Formula and method
Formula
Mifflin–St Jeor: BMR = 10w + 6.25h − 5a + 5 (men) or − 161 (women), w in kg, h in cm, a in years
Rounded to whole kcal/day.
Estimated calories burned at rest per day. Revised Harris–Benedict is shown for comparison. Informational estimate, not medical advice. Talk to a qualified health professional about your own situation.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Units = Metric (kg, cm); Sex = Male; Weight (kg, or lb) = 70; Height (cm, or in) = 175; Age = 30.
| Result | Value |
|---|---|
| Basal metabolic rate | 1,649 kcal/day |
| Harris–Benedict (revised) | 1,696 |
Example 2
Inputs: Units = Metric (kg, cm); Sex = Female; Weight (kg, or lb) = 70; Height (cm, or in) = 175; Age = 30.
| Result | Value |
|---|---|
| Basal metabolic rate | 1,483 kcal/day |
| Harris–Benedict (revised) | 1,507 |
The first line is the headline result (basal metabolic rate). Below it the bMR Calculator lists harris–Benedict (revised), which describe the same case from other angles. Rounded to whole kcal/day.
The two equations
Mifflin–St Jeor: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, or − 161 for women. For a 30-year-old man who weighs 70 kg and is 175 cm tall: 700 + 1,093.75 − 150 + 5 = 1,648.75, shown as 1,649 kcal per day.
Revised Harris–Benedict for men: 13.397 × weight + 4.799 × height − 5.677 × age + 88.362. For the same man: 937.79 + 839.83 − 170.31 + 88.36 = 1,695.67, shown as 1,696 kcal. The two equations differ by a few per cent, which is the size of uncertainty to expect in any BMR estimate.
How age changes BMR
A 70 kg, 175 cm man at different ages.
Every figure in this table comes from running this calculator, so it matches what the form returns.
| Age (years) | Basal metabolic rate | Harris–Benedict (revised) |
|---|---|---|
| 20 | 1,699 | 1,752 |
| 30 | 1,649 | 1,696 |
| 40 | 1,599 | 1,639 |
| 50 | 1,549 | 1,582 |
| 60 | 1,499 | 1,525 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Age: entering "10" shows "Age must be at least 15." beside that field and no result.
Choosing between the BMR Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [BMI Calculator](/health/bmi-calculator/) | units, weight and height | Your BMI |
| [TDEE Calculator](/health/tdee-calculator/) | units, sex and weight | Total daily energy expenditure |
| [Calorie Calculator](/health/calorie-calculator/) | units, sex and weight | Maintenance calories |
| [Macro Calculator](/health/macro-calculator/) | daily calories, carbohydrate and protein | Carbohydrate |
| [Protein Calculator](/health/protein-calculator/) | units, body weight and profile | Protein per day |
Background: nutrition estimates
Nutrition calculators estimate: they use population-average equations and food tables, and different tables give different numbers for the same food. Certain medical conditions change energy needs in ways basic formulas cannot see, and only laboratory analysis gives exact nutrient values.
Use the result as a starting point, track what actually happens over a few weeks and adjust; ask a qualified professional about medical or clinical decisions.
Assumptions and limitations
- Ages 15–100
- Estimates vary by ±10% or more between individuals
- Not a diagnosis
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for age to confirm this.
Frequently asked questions
What does the BMR Calculator calculate?
Estimate basal metabolic rate with the Mifflin–St Jeor and revised Harris–Benedict equations. It returns Basal metabolic rate and Harris–Benedict (revised).
What formula does the BMR Calculator use?
Mifflin–St Jeor: BMR = 10w + 6.25h − 5a + 5 (men) or − 161 (women), w in kg, h in cm, a in years. Estimated calories burned at rest per day.
What do I need to enter in the bMR Calculator?
You enter Units, Sex, Weight (kg, or lb), Height (cm, or in) and Age (years).
How is the result rounded or limited?
Rounded to whole kcal/day. Ages 15–100.
What are the limits of this calculator?
Ages 15–100. Estimates vary by ±10% or more between individuals. Not a diagnosis.
What does the “Units” option change?
It sets how the bMR is worked out. The choices are Metric (kg, cm) and Imperial (lb, in).
What is an example of a bMR result?
With units Metric (kg, cm), sex Male, weight (kg, or lb) 70, height (cm, or in) 175 and age 30, the basal metabolic rate is 1,649 kcal/day.
Where does the method come from?
The method follows: Mifflin MD et al., Am J Clin Nutr 1990;51:241–247; Roza AM, Shizgal HM, Am J Clin Nutr 1984;40:168–182 (revised Harris–Benedict).
Can I rely on this calculator for a decision?
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health. For this calculator in particular: Ages 15–100.
Related calculators
- BMI Calculator — Find your Body Mass Index (BMI) and weight status.
- TDEE Calculator — Total daily energy expenditure from BMR and activity level.
- Calorie Calculator — Daily calories to maintain, lose or gain weight.
- Macro Calculator — Split daily calories into grams of carbohydrate, protein and fat.
- Protein Calculator — Daily protein target by body weight and activity.
- Calories Burned Calculator — Estimate calories burned from activity, body weight and time using MET values.
- Carbohydrate Calculator — Daily carbohydrate range from calorie intake.
- Fat Intake Calculator — Daily fat range from calorie intake.
- Fiber Calculator — Daily fiber target from calorie intake.
Sources
- Mifflin MD et al., Am J Clin Nutr 1990;51:241–247
- Roza AM, Shizgal HM, Am J Clin Nutr 1984;40:168–182 (revised Harris–Benedict)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.