Most adults need roughly 1,800 to 2,800 calories a day, but your number depends on your age, size and activity. Here is how to estimate it, with worked examples in both calories and kilojoules.
There is no single number. Adults need roughly 1,800 to 2,800 calories (about 7,500 to 11,700 kJ) a day depending on age, sex, size and activity. Australian labels use an average adult reference of 8,700 kJ (about 2,079 calories), but your own figure can be quite different.
Start with your basal metabolic rate (BMR), the energy your body uses at rest, then multiply by an activity factor to get your total daily energy expenditure (TDEE). One widely used BMR formula is Mifflin-St Jeor:
| Activity level | Typical factor |
|---|---|
| Little or no exercise | 1.2 |
| Light exercise 1-3 days a week | 1.375 |
| Moderate exercise 3-5 days a week | 1.55 |
| Hard exercise 6-7 days a week | 1.725 |
Woman, 35, 70 kg, 165 cm, light exercise: BMR = 700 + 1,031 − 175 − 161 = about 1,395 calories. TDEE = 1,395 × 1.375 = about 1,918 calories (about 8,030 kJ).
Man, 35, 85 kg, 178 cm, moderate exercise: BMR = 850 + 1,113 − 175 + 5 = about 1,793 calories. TDEE = 1,793 × 1.55 = about 2,778 calories (about 11,620 kJ).
To lose weight, eat below your TDEE; to gain, eat above it. A moderate deficit is usually easier to keep up. See what is a good calorie deficit and what is a good calorie surplus. Very low-calorie diets should only be done under medical supervision.
What you eat matters as well as how much. The Australian Dietary Guidelines and the Eat for Health website (eatforhealth.gov.au) set out recommended food groups and serves for different ages. Children, teens, pregnant or breastfeeding women and people with health conditions have different needs, so speak to a doctor or accredited dietitian.
How many calories should I eat a day?
Most adults need roughly 1,800 to 2,800 calories (about 7,500 to 11,700 kJ) depending on age, sex, size and activity. Use a calculator for a personal estimate.
How many calories is 8,700 kJ?
About 2,079 calories. It is the average adult daily reference shown on Australian food labels.
How do I calculate my daily calories?
Estimate your BMR with a formula such as Mifflin-St Jeor, then multiply by an activity factor to get your TDEE.
How many calories should I eat to lose weight?
Eat below your TDEE. A moderate deficit is usually easier to sustain than a very large one. Speak to a doctor or dietitian before major changes.
Do kilojoules and calories differ in how they count?
No. They are two units for the same energy. 1 calorie is 4.184 kJ.