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Last updated 3 September 2026
BMR and TDEE, in plain terms
BMR is what your body would burn lying still all day — heartbeat, breathing, brain, temperature. It's the floor, and it accounts for most of what you burn even on an active day.
TDEE is BMR multiplied by an activity factor, and represents everything: moving around, exercise, digesting food. It's the number that matters for planning, because it's what you actually spend.
Using the goal targets
Eating at your TDEE holds your weight roughly steady. Eating below it loses weight, above it gains. The convention is that a 500 calorie daily deficit works out to around half a kilogram a week, since roughly 3,500 calories corresponds to half a kilo of fat — a rule of thumb rather than a law.
The extreme loss row is included for completeness, but a 1,000 calorie daily deficit is aggressive and hard to sustain, and can leave you short of nutrients. This calculator will not show a target below 800 calories for that reason.
Method, limitations and sources
Formula. Basal metabolic rate uses the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for men or −161 for women. Total daily energy expenditure multiplies that BMR by a standard activity factor, and the loss and gain targets adjust the total by a fixed calorie amount.
Inputs it needs. Sex, age, height, weight and activity level.
What it assumes. That your body composition and metabolism are close to the average of the group the equation was derived from — 498 healthy adults aged 19 to 78. It also assumes your self-reported activity level is accurate, which is where most of the error usually comes from: activity multipliers are broad categories, and people commonly place themselves a category too high.
Expected accuracy. Mifflin-St Jeor is generally the best-performing of the common prediction equations, but it still lands within 10% of a measured resting metabolic rate only most of the time, not always. For an individual, a couple of hundred calories of error is entirely ordinary. The practical approach is to treat the number as a starting point and adjust it against what actually happens over several weeks.
Where it is least reliable. Very muscular or very lean people, people with a high body weight, older adults, pregnant or breastfeeding women, children and teenagers, and anyone with a thyroid or metabolic condition or on medication that affects appetite or metabolism.
When not to use it. Do not use it to justify a very low calorie intake. Cutting deeply below your estimated needs is not a faster route to anything and carries real risks. If you are unwell, recovering from illness, pregnant, under 18, or have a history of disordered eating, this figure is not the right basis for a plan — speak to a doctor or a registered dietitian.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775–789.
- CDC — About Body Mass Index.
Common questions
What is the difference between BMR and TDEE?
BMR is what your body burns at complete rest just keeping you alive. TDEE is BMR multiplied by an activity factor, and represents everything you burn across a normal day including movement, exercise and digestion. TDEE is the number to plan meals around.
Which formula does this use?
Mifflin-St Jeor, using weight, height, age and sex. An Academy of Nutrition and Dietetics evidence review found it estimated resting metabolic rate to within 10% of measured values more often than the other equations in common clinical use. That is a comparison between equations, not a guarantee: errors larger than 10% are still common for any individual, and none of these formulas replaces a measured test.
Why is a 500 calorie deficit the usual advice for weight loss?
Roughly 3,500 calories corresponds to about half a kilogram of body fat, so a 500 calorie daily deficit works out near half a kilogram a week. It is a rule of thumb rather than a precise law, and real results vary between people.
Is this medical or dietary advice?
No. These are general estimates from a standard equation. Individual metabolism varies, and health conditions, medication and pregnancy all change the picture. Speak to a doctor or a registered dietitian for guidance specific to you.