Most adults need roughly 1,800 to 3,000 calories a day. Work out your resting burn (BMR) with the Mifflin-St Jeor formula, multiply it by your activity level, then eat 300 to 500 below that to lose fat or 200 to 300 above it to build muscle, and adjust after two or three weeks.
There is no single right number of calories. A tall man who trains five days a week can need twice as much food as a smaller person who sits most of the day. The good news: you can estimate your own number in a minute, then fine-tune it with two or three weeks of real data.
Step 1: your resting burn (BMR)
Your body burns energy even when you do nothing at all: breathing, keeping warm, running your brain and organs. This is your basal metabolic rate, or BMR. For most adults it is the biggest part of the day's burn, often 60 to 70 percent of it.
The most widely used formula today is Mifflin-St Jeor. It uses your weight, height, age and sex:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
For a 30-year-old man who weighs 80 kg and is 178 cm tall, that is 800 + 1,112 − 150 + 5 = about 1,770 calories a day at rest.
Step 2: add how much you move (TDEE)
Next, multiply your BMR by an activity factor to get your total daily energy expenditure, or TDEE. This is the number of calories that keeps your weight steady.
- Mostly sitting, little exercise: × 1.2
- Light exercise 1 to 3 days a week: × 1.375
- Moderate exercise 3 to 5 days a week: × 1.55
- Hard training 6 to 7 days a week: × 1.725
- Physical job and hard training: × 1.9
Our example man trains four days a week, so 1,770 × 1.55 is roughly 2,740 calories a day to keep his weight where it is.
Most people overestimate how active they are. If you are unsure, pick the lower level.
Step 3: set the number for your goal
- To lose fat: eat about 300 to 500 calories below your TDEE. That usually means losing around 0.5 percent of your bodyweight a week, which is fast enough to see and slow enough to keep your muscle.
- To keep your weight: eat at your TDEE.
- To build muscle: eat about 200 to 300 calories above it, and train hard. A bigger surplus mostly adds fat, not more muscle.
Avoid going very low. Cutting 1,000 calories or more a day leaves you tired, hungry and weaker in the gym, and it is much harder to keep going for long enough to matter.
Step 4: check it against real life
Every formula is an estimate. Two people with the same numbers can burn a few hundred calories apart. So treat your number as a starting point:
- Eat at your target for two to three weeks.
- Weigh yourself in the morning, after the toilet, three or more times a week.
- Compare the weekly average, not single days. Water and salt can move the scale by a kilo overnight.
- If the average is not moving the way you want, adjust by 100 to 200 calories and repeat.
Calories are not the whole story
Hitting your calories is what moves your weight, but what makes up those calories decides how you feel and what that weight is made of. Get enough protein (see how much protein you need), fill half your plate with vegetables, and keep most of your food close to how it grew. You will feel fuller on the same number of calories.
Sources
- The Mifflin-St Jeor equation: Mifflin et al., 1990
- Which resting-metabolism equations are most accurate: Frankenfield et al., 2005
The takeaway
Work out your BMR, multiply it by an honest activity level, then subtract or add a small amount for your goal. Track your weight for a few weeks and adjust. The calculator on this page does the maths for you, and the Shulah app keeps a running total of what you eat each day so you always know where you stand.