How Many Calories Do I Need a Day?

Step 1: Basal metabolic rate (BMR)

BMR is the energy your body uses at complete rest — breathing, circulation, keeping warm. The Mifflin–St Jeor equation is the most widely used estimate for adults.

Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. Women: the same, but − 161 instead of + 5.

Step 2: Multiply by an activity factor

Your total daily energy expenditure is BMR times an activity multiplier.

• 1.2 — little or no exercise
• 1.375 — light exercise 1–3 days a week
• 1.55 — moderate exercise 3–5 days a week
• 1.725 — hard exercise 6–7 days a week
• 1.9 — very hard exercise or a physical job

Worked example

A 30-year-old man, 80 kg and 180 cm: 800 + 1,125 − 150 + 5 = 1,780 kcal BMR. With little exercise (× 1.2) he needs about 2,136 kcal a day to keep his weight steady.

A 30-year-old woman, 60 kg and 165 cm: 600 + 1,031.25 − 150 − 161 ≈ 1,320 kcal BMR. With moderate exercise (× 1.55) that is about 2,047 kcal a day.

Losing or gaining weight

A common rule of thumb is that eating about 500 kcal less than maintenance per day leads to roughly 0.5 kg of weight loss per week, and 500 kcal more leads to a similar gain. Real results vary because the body adapts over time.

Very low intakes are hard to sustain and can miss important nutrients, so large cuts are best discussed with a professional.

Limits of any calorie estimate

Formulas cannot see muscle mass, hormones, medication or health conditions, so two people with the same numbers can differ by a few hundred calories. Treat the result as a starting point and adjust based on how your weight changes over a few weeks.

This is general information, not medical advice. Pregnant people, teenagers and anyone with a health condition should get advice from a doctor or dietitian.