To calculate your calorie intake, you need two things: your basal metabolic rate (the calories your body burns at rest) and a multiplier that accounts for how active you are. The result is your total daily energy expenditure, or TDEE, which is the number of calories you need to maintain your current weight. From there, you adjust up or down depending on whether you want to lose fat, gain muscle, or stay where you are.
Step 1: Find Your Basal Metabolic Rate
Your basal metabolic rate (BMR) is the energy your body uses just to keep you alive: breathing, circulating blood, regulating temperature, repairing cells. It accounts for the largest share of the calories you burn each day. The most widely recommended formula for estimating it is the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics considers the most accurate for most people.
The equations use weight in kilograms, height in centimeters, and age in years:
- Men: (9.99 × weight) + (6.25 × height) − (4.92 × age) + 5
- Women: (9.99 × weight) + (6.25 × height) − (4.92 × age) − 161
To convert: divide your weight in pounds by 2.2 to get kilograms, and multiply your height in inches by 2.54 to get centimeters. So a 35-year-old woman who weighs 150 pounds (68 kg) and stands 5’6″ (167.6 cm) would calculate: (9.99 × 68) + (6.25 × 167.6) − (4.92 × 35) − 161, which comes out to roughly 1,400 calories per day at rest.
Step 2: Factor in Your Activity Level
Your BMR only covers what your body burns lying still. To get your actual daily calorie needs, multiply your BMR by an activity factor that reflects how much you move throughout the day. This includes both structured exercise and everyday movement like walking, standing at work, or chasing kids around.
- Sedentary (desk job, little or no exercise): BMR × 1.2
- Somewhat active (desk job, exercise 1–2 days per week): BMR × 1.3
- Moderately active (active job or exercise 3 days per week): BMR × 1.4
- Above average (on your feet all day, exercise 4–5 days per week): BMR × 1.5
- Very active (physical job, intense exercise 6 days per week): BMR × 1.6
- Extremely active (heavy labor plus daily intense training): BMR × 1.7
Using the example above, that 35-year-old woman with a BMR of 1,400 who exercises three days a week would multiply by 1.4, giving her a TDEE of about 1,960 calories per day. That’s roughly what she’d need to eat to maintain her current weight.
Most people overestimate their activity level. If you’re unsure, start with the lower multiplier and adjust after two to three weeks based on what actually happens to your weight.
If You Know Your Body Fat Percentage
The Mifflin-St Jeor equation uses total body weight, which means it treats a pound of muscle the same as a pound of fat. That’s a problem for people who carry significantly more muscle or significantly more fat than average, because lean tissue burns far more calories at rest than fat tissue does.
If you know your body fat percentage (from a DEXA scan, skinfold calipers, or a reliable smart scale), you can use the Katch-McArdle formula instead. First, calculate your lean body mass: multiply your total weight in kilograms by your body fat percentage, then subtract that from your total weight. Then plug it in:
BMR = 370 + (21.6 × lean body mass in kg)
A muscular 180-pound man at 12% body fat has about 71.7 kg of lean mass, giving him a BMR of roughly 1,919 calories. The standard Mifflin-St Jeor equation might estimate him lower because it doesn’t account for his above-average muscle mass. For athletes and people who strength train consistently, this formula tends to be more accurate.
Adjusting for Weight Loss
Once you have your TDEE, losing weight means eating below it. A daily deficit of about 500 calories typically produces a loss of half a pound to one pound per week. This varies by body size, sex, and how long you’ve been in a deficit, but it’s a reliable starting point for most people.
You may have heard the old rule that 3,500 calories equals one pound of fat. That math is roughly correct for small, short-term changes in overweight individuals, but it breaks down over time. Your body adapts to a calorie deficit by gradually burning fewer calories. You move a little less without realizing it, your digestion becomes slightly more efficient, and hormonal shifts slow your metabolism. This is why weight loss stalls after several weeks even when you haven’t changed your eating. The old rule assumes your metabolism stays static, which it never does.
This adaptation is also why going too low backfires. For most people, eating fewer than about 1,200 calories a day can slow metabolism enough to make further fat loss harder, not easier. A moderate deficit of 300 to 500 calories below your TDEE is sustainable and protects against muscle loss.
Adjusting for Muscle Gain
Building muscle requires a calorie surplus, meaning you eat more than your TDEE. The current consensus is that a surplus of 300 to 500 calories per day hits the sweet spot: enough extra energy to support muscle growth while minimizing unnecessary fat gain. Eating 1,000 calories over your TDEE won’t build muscle twice as fast. It will just add more fat alongside whatever muscle you’re gaining.
Where those extra calories come from matters. Protein has the highest thermic effect of any macronutrient, meaning your body uses 15 to 30% of protein calories just to digest and process it. Carbohydrates use 5 to 10%, and fats use only 0 to 3%. This doesn’t mean you should eat only protein, but it does mean that a higher-protein surplus is more efficient for muscle building than one loaded with fat.
Why Your Number Is an Estimate
Every calorie formula is an approximation. Two people of the same height, weight, age, and sex can have meaningfully different metabolic rates based on genetics, muscle mass, hormonal health, sleep quality, and something called non-exercise activity thermogenesis, or NEAT. NEAT is all the movement you do that isn’t formal exercise: fidgeting, walking to the kitchen, gesturing while you talk, standing instead of sitting. Research from the Mayo Clinic found that NEAT can differ by up to 2,000 calories a day between two people of similar size. That’s an enormous variable that no formula captures.
This is why the calculated number is a starting point, not a verdict. Use it for two to three weeks, track what happens to your weight, and then adjust. If you’re trying to lose weight and the scale isn’t moving after three weeks at your calculated deficit, drop another 100 to 150 calories and reassess. If you’re trying to gain and the scale hasn’t budged, add 100 to 200 more. Real-world feedback always beats a formula.
How to Count What You Eat
Knowing your target number only helps if you can roughly track what’s going in. Every gram of the three major macronutrients carries a set calorie value: protein has 4 calories per gram, carbohydrates have 4 calories per gram, and fat has 9 calories per gram. Alcohol, for reference, sits at 7 calories per gram. This is why fatty foods are so calorie-dense and why a tablespoon of olive oil (about 120 calories) packs more energy than a tablespoon of sugar (about 48 calories).
A food scale and a tracking app make this practical. Weigh your portions for the first few weeks until you can eyeball reasonable estimates. Most people are surprised by how small a true “serving” of peanut butter or pasta actually is. You don’t need to track forever. A few weeks of careful measurement builds a mental calibration that lasts, and many people eventually maintain their targets without logging every meal.