A worked example
A 30-year-old woman, 170 cm and 75 kg, burns around 1,500 kcal a day at rest by Mifflin-St Jeor. Training 1 to 3 hours a week and on her feet a lot, she lands at moderate activity: about 2,330 kcal. With a desk job instead it would be 2,070 kcal, which shows how much the everyday part matters.
How TDEE is estimated
TDEE, total daily energy expenditure, is resting energy plus everything you do on top of it. The resting part comes from a formula. Mifflin-St Jeor uses weight, height, age and sex and is the one most dietitians reach for. Katch-McArdle uses lean mass instead, so it needs your body fat percentage, and it tends to do better for very muscular people.
The resting figure is then multiplied by an activity factor from 1.2 to 1.9. Your two answers pick the factor with the same table Ampsu uses at sign-up. The factors are broad categories, and one level up or down moves the answer by a couple of hundred calories, which is why the page shows all five.
| Training per week | Mostly seated | On feet a lot | Heavy physical |
|---|---|---|---|
| None | Sedentary (×1.2) | Lightly active (×1.375) | Moderately active (×1.55) |
| 1–3 hours | Lightly active (×1.375) | Moderately active (×1.55) | Very active (×1.725) |
| 4–6 hours | Moderately active (×1.55) | Very active (×1.725) | Very active (×1.725) |
| 7+ hours | Very active (×1.725) | Very active (×1.725) | Extremely active (×1.9) |
Turning it into a target
The targets use the same presets Ampsu offers when you pick a goal: 250, 500 or 750 kcal a day under your burn to lose, 250 over it to gain. The app also has a 1000 kcal deficit and a 500 kcal surplus for faster changes. A kilogram of body fat is about 7700 kcal, which is where the weekly rate comes from. Targets for losing never go below 1200 kcal a day, so for a small, less active person the faster options can land on the same number, and one that would sit at or above the burn isn’t shown.
How accurate is it?
For most people Mifflin-St Jeor lands within about 10% of a measured resting rate, which is a few hundred calories either way once activity is added. Treat the result as a starting point. Eat to it for two or three weeks, watch the scale trend, and adjust. The adaptive TDEE calculator turns that log into a number of your own.
Questions people ask
How should I answer the two questions?
Count the training you actually do in a normal week, not the plan. And think of a typical workday for the second one: a desk job with a walk at lunch is still mostly seated. Most people overestimate, so if you’re between two answers, take the lower one and adjust after a couple of weeks.
Should I eat back the calories from a workout?
Not if your training is already in the first answer. That would count it twice.
Why does the result depend on sex?
Mifflin-St Jeor was fitted separately for women and men, because at the same size a female body tends to carry less lean mass. The two versions differ by a fixed 166 kcal a day. Enter a body fat figure and the estimate uses lean mass instead.
How many calories should I eat to lose weight?
A deficit of around 300 to 500 kcal below your TDEE is a common, sustainable place to start. The macro calculator helps split that target into protein, fat and carbs.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990
- Comparison of resting energy expenditure equations, including Katch-McArdle. Nutrients, 2022
- Physical activity level categories, in Dietary Reference Intakes for Energy (NASEM, 2023)