How many calories should I eat a day?

Step 1: your resting energy

Resting energy is what your body burns at rest. The Mifflin-St Jeor equation, published in 1990, estimates it from weight, height and age ^[1]:

Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

Step 2: multiply by how active you are

These activity factors are commonly used to turn resting energy into a daily total ^[2]. They are a rule of thumb, not a government standard.

How active you are	Multiply by
Mostly sitting	1.2
Light exercise 1–3 days a week	1.375
Moderately active	1.55
Very active	1.725
Very hard daily training or a physical job	1.9

Two worked examples

A 35-year-old woman, 70 kg, 165 cm, light exercise: 700 + 1,031 − 175 − 161 = 1,395 kcal at rest. × 1.375 = about 1,920 kcal a day.
A 35-year-old man, 85 kg, 180 cm, moderate exercise: 850 + 1,125 − 175 + 5 = 1,805 kcal at rest. × 1.55 = about 2,800 kcal a day.

How much less to eat to lose weight

The CDC says people who lose about 1 to 2 pounds a week are more likely to keep it off ^[3]. The NHS gives the same range: 0.5 to 1 kg a week ^[4].

Older advice says 3,500 kcal equals one pound. NIH researcher Kevin Hall showed this rule overestimates weight loss, because your body adapts as you eat less ^[5]. Loss slows over time. The free NIH Body Weight Planner models this ^[6].

Very low calorie diets are not suitable or safe for everyone, says the NHS ^[7]. Talk to a doctor before going very low.

Your number is a starting point

Every formula is an estimate. Track for two to three weeks, watch your weight trend, and adjust by small steps.

Quick answers

What is the most accurate formula for daily calories?

The Mifflin-St Jeor equation is widely used to estimate resting energy. Multiply it by an activity factor for a daily total. Treat the result as an estimate and adjust it using your weight trend.

How fast should I lose weight?

The CDC and NHS both point to about 1 to 2 pounds (0.5 to 1 kg) a week. People who lose weight at that pace are more likely to keep it off.

Does 3,500 calories equal one pound?

Not over time. NIH research shows the 3,500-calorie rule overestimates weight loss, because the body adapts as you eat less.

Sources

Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990. pubmed.ncbi.nlm.nih.gov

University of Kansas, American Indian Health: Exercise and calorie needs. aihd.ku.edu

CDC. Steps for losing weight. www.cdc.gov

NHS. Tips to help you lose weight. www.nhs.uk

Hall KD. Why is the 3500 kcal per pound weight loss rule wrong? pmc.ncbi.nlm.nih.gov

NIDDK. NIH Body Weight Planner. www.niddk.nih.gov

NHS. Overweight and obesity in adults: treatment. www.nhs.uk

General information, not medical advice. Talk to a doctor or registered dietitian about your own needs.