BMR vs TDEE vs RMR: what each number means

BMR is the energy your body burns at complete rest, measured after sleep and 12 or more hours without food.^[1] RMR is measured under looser conditions and runs about 10% higher.^[1] TDEE is everything you burn in a day: resting burn plus digesting food plus movement.^[1]

The three numbers side by side

• BMR (basal metabolic rate). The least energy compatible with life, at complete physical, mental and digestive rest.^[1] It is measured lying down after sleep, before getting up, 12 or more hours after eating.^[1] It is 45% to 70% of daily burn, depending on age and lifestyle.^[2]
• RMR (resting metabolic rate). The energy used awake and resting, about 10% higher than BMR.^[1] It is measured lying down, with no food, drink or exercise for the prior 4 to 5 hours, and makes up about 60% to 70% of daily burn.^[1]
• TDEE (total daily energy expenditure). Resting burn plus the thermic effect of food plus physical activity.^[1] It is measured with doubly labeled water, the benchmark method for people living normally.^[3]

The roughly 10% gap between BMR and RMR is small next to the other uncertainties below.^[1] It matters most when you compare a lab report or two devices that report different measures.

What makes up TDEE

• Resting burn. The largest part, typically 60% to 70% of the total.^[1] Fat-free mass is the best single predictor of it.^[5] Fat tissue burns about 5 calories per kilogram, against 20 for fat-free mass.^[1]
• Digesting food. The thermic effect of food typically accounts for about 10% of daily burn.^[1] Protein costs the most to process, at 20% to 30% of its calories, against 0% to 3% for fat.^[1]
• Activity. This is the part that varies most. It covers exercise and everyday moving around, like fidgeting and walking, which is called NEAT.^[1]

Movement is why two people of the same size can need very different amounts of food. One review found that NEAT alone varies by 2,000 calories a day between two people of similar size, because of their jobs and leisure time.^[4] Activity ranges from 15% of daily burn for sedentary people up to 50% for physically active people.^[1]

Which number a BMR calculator gives you

Our calculator, like the Dalia app, uses the Mifflin-St Jeor equation and labels the result BMR. The equation was built from 498 healthy adults.^[5] Their resting burn was measured with lab equipment (indirect calorimetry).^[5] So the number predicts resting burn, which is closer to RMR than to a strict BMR.

A 2005 review of four common equations found Mifflin-St Jeor the most reliable, landing within 10% of measured RMR for more people than any other.^[6] The same review warned of noteworthy errors when it is applied to individuals.^[6] It also noted that older adults and US ethnic minorities were underrepresented in the studies.^[6]

Newer studies show the size of those misses. In 132 young Spanish adults, Mifflin-St Jeor was within 10% for 61% of normal-weight women.^[7] In 41 young Chilean women, it overestimated resting burn by 203.0 calories a day in those with overweight and 176.6 in those with obesity.^[8] It still overestimated less than the other equations tested.^[8]

How each one is measured

Resting burn is most often measured by indirect calorimetry. You rest while a machine tracks the oxygen you use and the carbon dioxide you breathe out.^[1] BMR can only be measured in a lab.^[9]

TDEE is measured with doubly labeled water. You drink water tagged with natural, nonradioactive isotopes, and their washout over several days shows how much energy you used.^{[3, 2]} It is ideal for people living their normal lives, but it is costly and cannot show hour-to-hour changes.^[10]

Why your watch shows a different number

Watches and apps estimate resting and active burn with their own methods, so two devices can disagree with each other and with an online calculator. In studies of people going about their day, step counters had average errors of −62.3% to −0.8% for calories burned.^[10] Treat any device number as an estimate, and compare it with itself over time rather than with another device.

For more on the daily number, see what TDEE is. To run your own numbers, use the TDEE and BMR calculator. To turn the estimate into a target, see calories and macros, explained and how many calories to eat to lose weight.

Should you eat below your BMR?

A 2026 US guideline says intensive weight loss programs should aim for a calorie deficit of 500 to 750 calories a day.^[18] Taken off TDEE, that can land below BMR for some people. The older 2013 US obesity guideline listed 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men, usually adjusted for body weight.^[12] That 2013 guideline kept very low calorie diets, under 800 calories a day, for medical settings with trained practitioners.^[12]

Your numbers change over time

Daily burn, adjusted for fat-free mass, stays stable from about age 20 to 60, then declines.^[13] Large weight loss lowers resting burn too.^[14] Whether it drops by more than the smaller body explains is disputed.^[15]

In 14 Biggest Loser contestants, resting burn was 499 calories a day lower than expected 6 years after extreme weight loss.^[14] In 171 women with overweight who lost weight on a diet program, the extra drop was about 54 calories a day.^[15] It did not predict who regained weight over 2 years.^[15] The National Academies advise watching your weight over time and adjusting what you eat as needed.^[16]

When to talk to a clinician