What are basal metabolic rate (BMR) and daily energy expenditure (TDEE)?
Basal metabolic rate (BMR) is the amount of energy your body uses at complete rest – to run your heart, lungs, brain and other organs. The calculator works it out with the Mifflin-St Jeor equation: for men, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5; for women, the last term is −161 instead of +5.
Total daily energy expenditure (TDEE) is how much energy your body uses over a full day, once movement, work and digesting food are added to the basal metabolic rate. The calculator gets TDEE by multiplying BMR by an activity factor that matches the activity level you chose.
What do the activity levels and activity factors mean?
The activity factor is the number the calculator multiplies BMR by: 1.2 for a mostly sedentary lifestyle, 1.375 for light activity (moving once to three times a week), 1.55 for moderate activity (three to five times a week).
For high activity (intense exercise six to seven times a week) the calculator uses a factor of 1.725, and for very high activity (a physical job combined with regular training) it uses 1.9. Pick the level that describes your usual week, not a single unusual day.
Why the result is an estimate, and kcal versus kJ
Reviews often list the Mifflin-St Jeor equation among the more accurate simple estimates of BMR, but it remains an estimate: actual energy use varies between people even at the same weight, height and age, and a difference of around 10% is common. The European Food Safety Authority (EFSA) publishes dietary reference values for energy intake in adults, based on similar calculations.
The energy in food and the energy your body uses can be expressed in kilocalories (kcal) or kilojoules (kJ); 1 kcal equals 4.184 kJ. The calculator is meant for adults aged 18 and over and is not suitable during pregnancy or breastfeeding, when energy needs change. For personal nutrition goals, the best person to talk to is a doctor or a registered dietitian.
Frequently asked questions
How many calories a day do I need?
It depends on your sex, age, height, weight and activity level. The calculator above first works out your basal metabolic rate (BMR), then estimates your total daily energy expenditure (TDEE) from the activity level you choose.
What is basal metabolic rate (BMR)?
BMR is the energy your body uses at complete rest, just to run its organs. It is calculated with the Mifflin-St Jeor equation from your sex, weight, height and age.
What is TDEE?
TDEE (total daily energy expenditure) is BMR multiplied by an activity factor based on how active you are – from 1.2 for a sedentary lifestyle to 1.9 for very high activity.
How many kJ is 1 kcal?
1 kilocalorie (kcal) equals 4.184 kilojoules (kJ). Food labels in the EU often show energy in both units for this reason.
Is the calorie calculator suitable during pregnancy?
No. The calculator is built for adults aged 18 and over and does not account for the changed energy needs of pregnancy or breastfeeding. Talk to a doctor or dietitian instead.
Sources
- Mifflin MD et al. – A new predictive equation for resting energy expenditure in healthy individuals (1990)
- EFSA – Scientific Opinion on Dietary Reference Values for energy (2013)
- FAO/WHO/UNU – Human energy requirements (2004)
Updated: October 2026
For information only, not a substitute for medical advice.