Resting Metabolic Rate Calculator
Enter your age, sex, height and weight to estimate how many calories your body burns at rest in a day. Two well-known equations are shown side by side so you can see how far they agree.
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Created by the Reeliy Editorial Team. Last updated: Oct 19, 2026
What resting metabolic rate is
Resting metabolic rate (RMR), also called resting energy expenditure (REE), is the energy your body uses in a day while at rest. It pays for breathing, circulation, keeping body temperature steady, running the brain and repairing tissue. For most adults it is the largest single part of daily energy use, typically 60 to 75 percent of the total.
RMR is the starting point for nearly every calorie plan. Multiply it by an activity factor and you get total daily energy expenditure, which you can explore with the TDEE calculator. Subtract or add to that figure to set a target for weight loss or gain.
RMR versus BMR
Basal metabolic rate (BMR) is measured under tighter conditions: after a night's sleep, fasted, lying still in a thermally neutral room. RMR is measured under looser conditions, so it tends to come out slightly higher, often by about ten percent. In practice the prediction equations are fitted to either kind of measurement and the two names are used almost interchangeably. Our BMR calculator uses the same idea with its own set of formulas.
How to use the calculator
Choose US or metric units, enter your age and sex, then your height and weight. Weight has its own unit menu and metric height can be entered in centimetres or metres. Blank age or height boxes are treated as zero, so fill them in. The results are given in calories (kilocalories) per day, rounded to the nearest whole number.
The two equations
Both equations take weight in kilograms (kg), height in centimetres (cm) and age in years.
Mifflin-St Jeor
Published in 1990 from measurements on healthy people of normal weight and with obesity, this is the equation most dietetic guidance recommends today.
men: RMR = 10 × kg + 6.25 × cm − 5 × age + 5
women: RMR = 10 × kg + 6.25 × cm − 5 × age − 161
Harris-Benedict
The older equation comes from data collected in the early twentieth century and was published by James Harris and Francis Benedict. The calculator uses the original coefficients:
men: RMR = 66.473 + 13.7516 × kg + 5.0033 × cm − 6.755 × age
women: RMR = 655.0955 + 9.5634 × kg + 1.8496 × cm − 4.6756 × age
Worked example
A 45-year-old woman, 165 cm tall, weighing 68 kg:
- Mifflin-St Jeor: 10 × 68 + 6.25 × 165 − 5 × 45 − 161 = 680 + 1,031.25 − 225 − 161 = 1,325 calories per day.
- Harris-Benedict: 655.0955 + 9.5634 × 68 + 1.8496 × 165 − 4.6756 × 45 = 655.1 + 650.3 + 305.2 − 210.4 = 1,400 calories per day.
The gap of 75 calories is about 6 percent, a fairly typical disagreement between the two. For a 30-year-old man at 5 ft 10 in and 180 lb (177.8 cm, 81.6 kg) the pair is 1,783 and 1,876 calories.
How RMR changes with age and sex
Resting energy use falls with age, mostly because lean tissue declines. In the Mifflin-St Jeor equation each year costs 5 calories a day, so each decade costs 50. The table uses a fixed example body for each sex (a man of 175 cm and 70 kg, a woman of 165 cm and 60 kg) so only age varies.
| Age | Man: Mifflin | Man: Harris-Benedict | Woman: Mifflin | Woman: Harris-Benedict |
|---|---|---|---|---|
| 20 | 1,699 | 1,770 | 1,370 | 1,441 |
| 30 | 1,649 | 1,702 | 1,320 | 1,394 |
| 40 | 1,599 | 1,634 | 1,270 | 1,347 |
| 50 | 1,549 | 1,567 | 1,220 | 1,300 |
| 60 | 1,499 | 1,499 | 1,170 | 1,254 |
| 70 | 1,449 | 1,432 | 1,120 | 1,207 |
How accurate are RMR estimates?
Equations predict the average person of a given size, age and sex. Real people differ because of how much of their weight is lean tissue, thyroid function, recent dieting, medication, hormones and genetics. A review of predictive equations for healthy adults found that Mifflin-St Jeor was the one that came closest to measured values most often, yet even it misses by more than ten percent for a sizeable minority of people.
The gold standard is indirect calorimetry, in which a breathing mask or hood measures oxygen consumption and carbon dioxide output over 10 to 30 minutes while you rest. Some clinics and sports labs offer it. If you cannot get a test, treat your estimate as a first guess and adjust it using your weight trend across several weeks.
These are estimates for information only and are not medical advice. Do not use them to plan very low calorie diets without professional supervision. See our disclaimer.
Putting your RMR to use
- Multiply by an activity factor (1.2 for a desk job with no exercise up to about 1.9 for very hard training) to estimate total energy use; the calorie calculator automates this.
- Do not eat below your RMR for long periods without guidance. Intake that low usually leads to fatigue, lost muscle and a harder time sticking to the plan.
- Build lean mass if you can. Muscle burns more at rest than fat, and strength training also slows the age-related decline in RMR.
- Use the weight loss calorie calculator to choose a daily intake for a given pace.
Frequently asked questions
Which result should I use, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor is generally preferred because it was built from more recent data. Harris-Benedict tends to give a higher figure, particularly for younger people. If the two differ by a lot, take the Mifflin figure or average them.
What is the difference between RMR and TDEE?
RMR is what you burn at rest. TDEE (total daily energy expenditure) adds the energy for movement, exercise and digesting food, so it is always higher than RMR.
Does the calculator work for children?
Both equations were fitted to adults, so the results are not reliable for children or teenagers who are still growing.
How many calories is my RMR in kilojoules?
Multiply calories by 4.184. For example, 1,500 calories per day is about 6,276 kJ per day.
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51(2):241-247.
- Harris JA, Benedict FG (1918). A biometric study of human basal metabolism. Proceedings of the National Academy of Sciences 4(12):370-373.
- Frankenfield D, Roth-Yousey L, Compher C (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association 105(5):775-789.
Cite this calculator and page
If you use this page in your work, you can cite it as:
Reeliy Editorial Team. (2026). Resting Metabolic Rate Calculator. Reeliy. https://reeliy.com/calculators/rmr-calculator“Resting Metabolic Rate Calculator.” Reeliy, 2026, https://reeliy.com/calculators/rmr-calculator.