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How the TDEE calculator works
The calculator follows three steps, the same ones the Calorix app uses when it sets your daily targets.
1. Your resting energy (BMR)
First it estimates your basal metabolic rate with the Mifflin-St Jeor equation, which was built from resting energy measurements of 498 healthy adults aged 19 to 78, including people of normal weight and people with obesity:
- Men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
- Women: 10 × weight in kg + 6.25 × height in cm − 5 × age − 161
- Other: the same formula with −78, the midpoint of the two
2. Your activity
Next it multiplies your BMR by an activity factor:
| Activity level | What it looks like | Factor |
|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.2 |
| Lightly active | Light exercise 1 to 3 days a week | 1.375 |
| Moderately active | Moderate exercise 3 to 5 days a week | 1.55 |
| Very active | Hard exercise 6 to 7 days a week | 1.725 |
| Extremely active | Physical job or training twice a day | 1.9 |
The result is your TDEE, also called your maintenance calories.
3. Targets for your goal
To lose or gain weight, the calculator subtracts or adds energy based on a weekly pace, using the common estimate of about 7,700 kcal per kilogram of body weight. Losing 0.5 kg a week, for example, means about 550 kcal a day below your TDEE.
Two safety rules apply, exactly as in the app:
- Pace limit. The weekly pace is capped at 1% of your body weight, and anything above 0.75% is flagged. The CDC notes that people who lose weight at a gradual pace of about 1 to 2 pounds a week are more likely to keep it off.
- Calorie minimum. Targets never go below 1,200 kcal for women, 1,500 kcal for men or 1,350 kcal for “other”, the midpoint. The 2013 AHA/ACC/TOS obesity guideline describes reduced-calorie diets of 1,200 to 1,500 kcal a day for women and 1,500 to 1,800 kcal for men; Calorix uses the low end of each range as its minimum.
Calorie targets are rounded to the nearest 10 kcal, as in the app.
A worked example
Take a 30-year-old man who is 180 cm tall, weighs 80 kg and is moderately active:
- BMR = 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal
- TDEE = 1,780 × 1.55 = 2,759 kcal, shown as 2,760 kcal a day
- To lose 0.5 kg a week: 2,759 − 550 = 2,209 kcal, shown as 2,210 kcal a day
That pace sits below his 0.75% warning point (0.6 kg a week) and his 1% cap (0.8 kg a week), and 2,210 kcal is well above his 1,500 kcal minimum, so no adjustment is needed.
Teens are different
The calculators on this site are for adults. For teenagers, the Calorix app uses the Institute of Medicine’s estimated energy requirement, which includes the energy needed for growth, and it never sets a calorie deficit for anyone under 18. If you’re a parent with questions about a teen’s weight, a pediatrician is the right person to ask.
How accurate is your result?
Any formula gives an estimate, not a measurement. In a systematic review of predictive equations, Mifflin-St Jeor estimated resting metabolism within 10% of the measured value for more people than the other common equations, and had the narrowest error range. The same review notes that errors can still be meaningful for an individual, and that older adults and some ethnic groups were underrepresented in the research.
Activity factors add their own uncertainty, because people tend to overestimate how active they are. A good way to handle both:
- Start with the number from this calculator.
- Log your food and weigh yourself regularly for two to three weeks.
- If your weight trend doesn’t match your goal, adjust your intake by 100 to 200 kcal and check again.
Expect change to be gradual. Modelling research published in The Lancet shows that the body’s response to a change in intake is slow, with a half-time of about a year, so early weeks are noisy and steady habits matter more than any single day.
TDEE, BMR and the calories on your watch
- BMR is the floor: what you’d burn lying still all day.
- TDEE is the whole day, including walking, working and training.
- Active calories from a watch or phone count only the movement part. Adding them to a TDEE that already includes your exercise would count them twice.
How Calorix uses your TDEE
When you set up Calorix, it runs this same calculation from your profile, then turns it into a daily calorie budget with protein, carbs, fat, fiber and water targets. If you connect Apple Health, you choose whether calories burned from workouts are added back, and the app avoids counting the same activity twice. Targets update automatically when your weight or goal changes.
Want to plan a goal date as well? Try the calorie deficit calculator, or split your calories into protein, carbs and fat with the macro calculator.
Updated October 9, 2026
