How Many Calories Should You Eat Per Day?
Calorie needs are not a single number. Here is how the published estimates are built, and how to work out a realistic figure for yourself.
What Determines Your Calorie Needs
Four factors account for most of the variation between people: body size, body composition, age, and physical activity. Larger bodies and higher muscle mass burn more at rest. Energy expenditure declines gradually with age, largely because lean mass tends to fall. Activity level is the largest modifiable factor and can easily swing daily needs by 500 calories or more. Genetics, hormones, and medications add further variation that formulas cannot capture.
How Basal Metabolic Rate Is Estimated
Basal metabolic rate (BMR) is the energy your body uses at complete rest. The Mifflin-St Jeor equation is currently among the most accurate general-population formulas. For men it is (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5. For women it is the same with 161 subtracted instead of 5 added. Multiplying BMR by an activity factor -- roughly 1.2 for sedentary through to 1.9 for extremely active -- gives total daily energy expenditure, or TDEE.
Average Intakes by Group
Published dietary reference values are useful as a sanity check. Adult women generally need somewhere between 1,600 and 2,400 calories per day depending on activity, while adult men typically need 2,000 to 3,000. These ranges are broad because they must cover sedentary desk workers and manual labourers alike. If your calculated number falls well outside the range for your group, it is worth checking your inputs before assuming the formula is wrong.
Applying the Number
Once you have a TDEE estimate, the practical step is to adjust it by goal. A deficit of about 500 calories per day is commonly associated with roughly 0.5 kg of loss per week, and a similar surplus with a comparable gain. Individual results vary, and a deficit that feels sustainable is more useful than a mathematically perfect one. Recalculate every few weeks as your weight changes, since the number moves with you.
Try It Yourself
Our Calorie Calculator applies the Mifflin-St Jeor formula and adjusts for your goal. If you want to see how those calories split across protein, carbohydrate, and fat, the Macro Calculator does that next.