How this calculator works
The calculator uses the Mifflin–St Jeor equation to estimate your resting energy use (basal metabolic rate), then multiplies it by an activity factor to estimate total daily energy. Kilocalories are multiplied by 4.184 to give kilojoules. The full method, with worked examples, is in how many kJ you should eat per day.
Reading your result
- Resting energy (BMR) is what your body uses at rest for breathing, circulation and other basic functions.
- Daily energy adds the energy from movement and activity, so it is the number to compare with your eating.
- Compare the result with the 8,700 kJ reference on Australian and New Zealand labels (2,079.35 kcal) to see how you differ from an average adult.
Limits of the estimate
This tool is for healthy adults aged 18 and over. It is an estimate and can be 10% or more away from your true needs. It does not replace advice from a doctor or accredited dietitian, especially during pregnancy or if you have a medical condition.
Frequently asked questions
Is this calculator accurate?
It gives a reasonable estimate for healthy adults, but individuals vary. Treat the result as a starting point.
Which formula does it use?
The Mifflin–St Jeor equation, followed by a standard activity multiplier.
Does it store my data?
No. The calculation runs in your browser and nothing you enter is sent to our server.
Last updated 11 Oct 2026. How we calculate.