The number of calories you need depends on your age, sex, size, and how active you are. As a rough starting point, the U.S. Dietary Guidelines estimate that adult women need 1,600 to 2,400 calories per day and adult men need 2,000 to 3,000. But those are wide ranges, and pinpointing your number takes a bit more detail.
General Calorie Ranges by Age and Sex
The 2020-2025 Dietary Guidelines for Americans break calorie needs into age brackets, with ranges that account for sedentary to active lifestyles:
- Women ages 19 to 30: 1,800 to 2,400 calories per day
- Men ages 19 to 30: 2,400 to 3,000 calories per day
- Women ages 31 to 59: 1,600 to 2,200 calories per day
- Men ages 31 to 59: 2,200 to 3,000 calories per day
- Women 60 and older: 1,600 to 2,200 calories per day
- Men 60 and older: 2,000 to 2,600 calories per day
If you’re sedentary, you’ll land near the bottom of those ranges. If you exercise most days, you’ll be closer to the top. These numbers assume average height and a healthy weight for each group, so they’re useful as a ballpark but not a personalized answer.
How to Calculate Your Personal Number
The most widely recommended method starts with your resting metabolic rate (RMR), the calories your body burns just to keep you alive: breathing, pumping blood, maintaining body temperature. The Mifflin-St Jeor equation, endorsed by the Academy of Nutrition and Dietetics, calculates it like this:
- Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
To convert your weight, divide pounds by 2.2. To convert height, multiply inches by 2.54. For example, a 35-year-old woman who is 5’6″ (167.6 cm) and weighs 150 pounds (68.2 kg) would get: (10 × 68.2) + (6.25 × 167.6) – (5 × 35) – 161 = roughly 1,392 calories at rest.
That number only covers survival. To account for everything else you do during the day, multiply it by an activity factor:
- Sedentary (desk job, little exercise): multiply by 1.2
- Lightly active (exercise 1-3 days per week): multiply by 1.375
- Moderately active (exercise 3-5 days per week): multiply by 1.55
- Very active (hard exercise 6-7 days per week): multiply by 1.725
The woman in our example, if she exercises three times a week, would multiply 1,392 by 1.375, giving her roughly 1,914 calories per day to maintain her current weight. That final number is called your total daily energy expenditure, or TDEE. It’s the calorie level where your weight stays stable.
Adjusting for Weight Loss
Losing weight requires eating fewer calories than your body uses. A deficit of about 500 calories per day typically leads to roughly one pound of weight loss per week, since a pound of body fat stores around 3,500 calories. For the woman in our example, that would mean aiming for about 1,414 calories per day.
Going much below that gets tricky. Very low calorie intakes make it harder to get the vitamins and minerals you need, and they tend to increase hunger and fatigue in ways that make the diet hard to sustain. Most people do better with a moderate deficit they can stick with for months rather than a dramatic cut that lasts a few weeks. If you have a significant amount of weight to lose, the deficit can sometimes be larger because your maintenance calories are higher to begin with, but the 500-calorie-per-day reduction is a reliable starting point for most people.
Adjusting for Muscle Gain
Building muscle requires a calorie surplus, meaning you eat more than your maintenance level. The sweet spot for gaining muscle while limiting fat gain is about 10 to 20% above your daily maintenance calories. That works out to a gain of roughly 0.25 to 0.5% of your body weight per week.
If you’re newer to weight training (less than six months of consistent lifting), aim for the higher end of that surplus, around 20%. Your body responds more dramatically to new training stimulus and can put those extra calories to work building muscle. If you’ve been lifting for several years, the lower end (closer to 10%) is more appropriate because trained muscles grow more slowly and extra calories are more likely to be stored as fat. Using our earlier example, someone with a maintenance level of 3,000 calories would eat 3,300 to 3,600 calories per day during a building phase.
Why Your Metabolism Isn’t What You Think
A common belief is that metabolism steadily slows down starting in your 20s or 30s. Research published in Science tells a different story. A large study analyzing energy expenditure across the lifespan found that both total and resting metabolic rates stay remarkably stable from ages 20 to 60, regardless of sex. The real decline begins around age 60, when calorie burn drops by about 0.7% per year, partly because of losses in muscle mass.
What does change in your 30s and 40s is often your activity level, not your metabolism itself. A desk job, less recreational exercise, and more time spent sitting can reduce your daily calorie burn by hundreds of calories without any shift in your underlying metabolic rate. That’s why the calorie ranges in the federal guidelines shrink slightly for older age groups, even though the biological slowdown hasn’t fully kicked in yet.
Where Your Calories Come From Matters
Not all calories are processed equally by your body. Your digestive system itself burns calories breaking down food, a phenomenon called the thermic effect of food. Protein costs the most energy to digest: 15 to 30% of protein calories are burned during digestion alone. Carbohydrates use 5 to 10%, and fats use just 0 to 3%. This means that 200 calories of chicken breast has a different net effect than 200 calories of butter, even though the number on the label is the same.
For overall health, a reasonable distribution of your daily calories looks like this: 45 to 65% from carbohydrates, 20 to 35% from fats, and 15 to 25% from protein. Within those ranges, people trying to lose weight or build muscle often benefit from pushing protein toward the higher end, both because of the higher digestive cost and because protein helps preserve muscle during a calorie deficit and supports muscle growth during a surplus.
In practical terms, if you’re eating 2,000 calories a day and aiming for 25% protein, that’s 500 calories from protein, or about 125 grams (since protein has 4 calories per gram). Carbs at 50% would be 1,000 calories, or 250 grams. Fat at 25% would be 500 calories, or about 56 grams (since fat has 9 calories per gram).
Putting It All Together
Start by calculating your resting metabolic rate with the Mifflin-St Jeor equation, then multiply by your activity factor. That gives you the number of calories needed to maintain your current weight. From there, subtract about 500 calories if you want to lose roughly a pound per week, or add 10 to 20% if you’re trying to build muscle with a consistent resistance training program.
Give any new calorie target two to three weeks before deciding it’s working or not. Weight fluctuates day to day based on water retention, food volume, and hormones. Track the trend over weeks, not days. If you’re losing more than about two pounds per week or gaining fat faster than expected during a surplus, adjust by 100 to 200 calories and reassess. Small, consistent changes are easier to stick with and far easier to fine-tune than dramatic swings in intake.