Your daily calorie need is your resting metabolism, from the Mifflin–St Jeor equation, multiplied by how active you are. A lightly active woman of 35, 70 kg and 168 cm needs about 1,944 kcal a day to keep her weight. Fill in your own details above in metric, US or UK units.
The formula
Resting energy expenditure (BMR), in kcal a day:
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Then multiply by the activity factor that matches your week:
| Activity level | Factor |
|---|---|
| Sedentary: desk job, little or no exercise | 1.2 |
| Lightly active: exercise 1–3 days a week | 1.375 |
| Moderately active: 3–5 days a week | 1.55 |
| Very active: 6–7 days a week | 1.725 |
| Extremely active: physical job plus training | 1.9 |
Most people overestimate their activity. If you are unsure, start one level lower and adjust after a few weeks.
Examples
| Person | BMR | Sedentary | Moderately active |
|---|---|---|---|
| Woman, 30, 60 kg, 165 cm | 1,320 | 1,584 | 2,046 |
| Woman, 50, 70 kg, 162 cm | 1,302 | 1,562 | 2,017 |
| Man, 30, 80 kg, 180 cm | 1,780 | 2,136 | 2,759 |
| Man, 60, 85 kg, 175 cm | 1,649 | 1,979 | 2,556 |
Calorie needs fall by about 5 kcal a day for every year of age, which is why the same diet that kept you stable at 30 can lead to slow weight gain at 50.
Losing or gaining weight
| Goal | Daily change | Expected pace |
|---|---|---|
| Lose slowly | −250 kcal | About 0.25 kg (½ lb) a week |
| Lose steadily | −500 kcal | About 0.5 kg (1 lb) a week |
| Gain slowly | +300 kcal | Lean gain with strength training |
The calculator never suggests eating below your BMR. Very low intakes make it hard to get enough protein and nutrients and are best done under medical supervision.
Calories and kilojoules
Food labels in the US and Europe show kcal (often written “Calories” with a capital C); in Australia and New Zealand kilojoules come first. To convert, multiply kcal by 4.184: 2,000 kcal is 8,368 kJ. The calculator shows both.
Keep in mind
Formulas estimate the average person with your measurements; real needs vary by about 10% either way. Track your weight for two or three weeks and adjust by 100–200 kcal if it moves when you expected it to stay put. Pregnancy, breastfeeding, illness and competitive sport change the numbers – ask a doctor or a registered dietitian.
The calculation runs on your device, and once zet4u is saved there it works offline too.
Frequently asked questions
How many calories should I eat a day?
It depends on your size, age, sex and activity. A moderately active 30-year-old woman of 60 kg and 165 cm needs about 2,050 kcal; a man of 80 kg and 180 cm about 2,750. The calculator gives your own estimate.
How many calories should I cut to lose weight?
A daily deficit of about 500 kcal leads to roughly 0.5 kg (1 lb) of weight loss a week for most adults. Faster loss is hard to keep up and can cost muscle.
What is BMR?
Basal metabolic rate: the energy your body uses at complete rest, just to stay alive. It is usually 60–70% of what you burn in a day.
Which formula does this calculator use?
The Mifflin–St Jeor equation (1990), which studies have found to be the most accurate of the common formulas for healthy adults. It is multiplied by a standard activity factor.
What is the difference between kcal and kJ?
They are two units of energy. One kilocalorie (what food labels call a Calorie) is 4.184 kilojoules. Labels in Australia and New Zealand list kilojoules first.
Sources
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