The short version
BMR estimates the energy your body would use at rest. TDEE estimates total daily energy expenditure after applying an activity factor. The calorie calculator starts with a BMR equation, multiplies by an activity level, then optionally adjusts the result for a weight-change goal.
Why the formula choice matters
Different calculators can disagree because they use different BMR equations. Mifflin-St Jeor uses age, sex, height and weight. Revised Harris-Benedict uses the same broad inputs but a different coefficient set. Katch-McArdle uses lean body mass, which means it depends on a body-fat estimate. That can be useful for some users, but it also imports the error of the body-fat estimate.
What moves the result most
- Body size: height and weight affect the base energy estimate.
- Activity level: this is often the least precise input because “moderate†or “active†can mean different things in real life.
- Goal rate: weight-loss or weight-gain targets are scenario assumptions, not medical instructions.
- Formula selection: Mifflin-St Jeor, Harris-Benedict and Katch-McArdle can produce different answers for the same person.
How to use the calorie calculator well
Start with maintenance calories, not an aggressive goal. Track your weight trend and energy level for a few weeks, then adjust. A calculator cannot know your metabolic adaptation, medication effects, training load, illness, pregnancy status, eating disorder risk or clinical needs.
Common mistakes
- Treating TDEE as a precise measurement instead of a starting estimate.
- Choosing a high activity factor because workouts feel hard, while daily movement outside training is low.
- Using Katch-McArdle with a guessed body-fat percentage and assuming it is automatically more accurate.
- Applying weight-change targets without considering nutrition quality, medical context or sustainability.
Related calculators
Concrete BMR and TDEE example
BMR is the estimated energy used at rest. TDEE adds activity. With the Mifflin-St Jeor method, a 35-year-old male at 80 kg and 180 cm has an estimated BMR of 1,730 kcal/day: 10 x 80 + 6.25 x 180 - 5 x 35 + 5. If the same person uses a moderate activity multiplier of 1.55, the TDEE estimate is about 2,682 kcal/day.
The biggest practical error is treating activity multipliers as measured data. A person who trains three times per week but sits most of the day can easily sit between two activity levels. That is why calorie calculator results work best as estimates, with a way to compare maintenance, deficit and surplus scenarios.
Formula choice matters
Mifflin-St Jeor is commonly preferred for modern adult calorie estimates, while Harris-Benedict variants are still widely seen in older tools. The page names the formula because two valid methods can produce different maintenance estimates for the same height, weight, age and sex.
FAQ
Is TDEE the same as maintenance calories?
In calculator use, TDEE is usually treated as a maintenance-calorie estimate. Real maintenance can differ because activity, tracking accuracy, water weight, metabolic adaptation and health factors vary.
Which BMR formula should I choose?
Mifflin-St Jeor is a common default when only age, sex, height and weight are known. Katch-McArdle can be useful when body-fat percentage is reasonably measured, but a guessed body-fat value can make it worse.
Can this tell me exactly how much to eat?
No. It gives a starting estimate. Nutrition decisions should account for health status, preferences, training, medical needs and observed weight trend.
References
- Mifflin et al.: A new predictive equation for resting energy expenditure in healthy individuals, accessed 2026-05-16.
- NIH / NIDDK Body Weight Planner, accessed 2026-05-16.
- EFSA: Dietary Reference Values for energy, accessed 2026-05-16.
Last reviewed: 2026-05-16.