Published by MetaSys Limited · Page updated · Editorial policy. Educational information; not a medical review.
How does the TDEE calculator work?
CalcFit uses the Mifflin–St Jeor equation to predict resting energy expenditure, then applies your selected activity factor to estimate daily energy use. The resting result is labelled BMR in the tool for familiarity; the original paper describes resting energy expenditure. Neither output is a laboratory measurement.
What formula does CalcFit use?
Resting kcal/day = 10 × weight in kg + 6.25 × height in cm − 5 × age in years + sex coefficient
The coefficient is +5 for the male equation and −161 for the female equation.
Estimated TDEE = resting kcal/day × activity factor
The coefficients come from Mifflin et al. (1990). The study developed a prediction equation from adult measurements. The two sex categories reflect that model; the calculator cannot account for every person's physiology, health condition or hormonal treatment.
A worked TDEE example
For a 30-year-old using the male equation, at 70 kg and 175 cm:
- Resting energy = (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 1,648.75 kcal/day.
- With the sedentary factor of 1.2: 1,648.75 × 1.2 = 1,978.5 kcal/day.
- The calculator rounds the displayed TDEE to 1,979 kcal/day.
These inputs are an arithmetic example. They are not a recommended body weight or calorie intake.
Which activity factor should I choose?
Consider a typical whole week, including work and everyday movement. The categories below are rough assumptions used by this tool; an exercise schedule alone does not measure your total activity. These multipliers are separate from the original resting-energy equation.
| Selection | Factor | Description in the tool |
|---|---|---|
| Sedentary | 1.2 | Desk job, little or no exercise |
| Lightly active | 1.375 | Light exercise 1–3 days/week |
| Moderately active | 1.55 | Moderate exercise 3–5 days/week |
| Very active | 1.725 | Hard exercise 6–7 days/week |
| Extra active | 1.9 | Physical job plus hard daily exercise |
For the example above, choosing moderate activity instead changes the estimate to 2,556 kcal/day. That difference illustrates why the activity assumption matters. It does not mean one selection is correct for you.
What can't a TDEE estimate tell you?
It cannot diagnose health, establish a safe calorie intake, or guarantee a rate of weight change. The tool's deficit and surplus scenarios are simple additions or subtractions, and its 30% protein / 40% carbohydrate / 30% fat split is an illustration, not an individualized nutrition recommendation.
For a model designed to explore changing energy needs over time, see the NIDDK Body Weight Planner and its eligibility guidance. Like this adult tool, it is not intended for children, pregnancy or breastfeeding. A qualified clinician or registered dietitian can help when results will inform a dietary change, particularly with a health condition or eating-disorder history.
Continue with the BMR calculator to explore resting energy, the macro calculator to understand a chosen calorie split, or our guide to interpreting calculator results.
Read Methodology & Sources and Calculator Limitations. Report an error.