The number of calories you need to maintain your weight depends on your size, age, sex, and how active you are, but most adults fall somewhere between 1,600 and 3,000 calories per day. You can get a personalized estimate by calculating your basal metabolic rate (the calories your body burns at rest) and then adjusting for your activity level. The result is your total daily energy expenditure, or TDEE, the number you need to eat around each day to keep your weight stable.
How Your Body Burns Calories
Your body uses energy in three main ways, and understanding them helps explain why two people of the same size can have very different maintenance calories.
The biggest chunk, about 60 to 70 percent of all the calories you burn, goes to basic survival functions: breathing, circulating blood, repairing cells, keeping your organs running. This is your resting metabolic rate, and it ticks along whether you’re sleeping or sitting on the couch. The second component is the energy your body spends digesting food, which accounts for roughly 10 percent of your daily burn. Protein-heavy meals cost more to digest (15 to 30 percent of the calories in protein get used up just processing it) compared to carbohydrates (5 to 10 percent) or fats (0 to 3 percent).
The third component is all your physical movement, both intentional exercise and everything else: walking to the kitchen, fidgeting, standing at your desk, carrying groceries. That “everything else” category can vary by up to 2,000 calories per day between two people of similar size, according to research from the Mayo Clinic. This is why someone with a physically active job or a restless temperament can eat significantly more without gaining weight.
Calculating Your Maintenance Calories
The most widely recommended formula for estimating resting metabolic rate is the Mifflin-St Jeor equation. The Academy of Nutrition and Dietetics considers it the most accurate option when you can’t get a lab measurement, predicting metabolic rate within 10 percent of the true value for about 70 percent of people.
The formulas use weight in kilograms, height in centimeters, and age in years:
- Men: (10 × weight) + (6.25 × height) − (5 × age) + 5
- Women: (10 × weight) + (6.25 × height) − (5 × age) − 161
To convert pounds to kilograms, divide by 2.2. To convert inches to centimeters, multiply by 2.54. For example, a 35-year-old woman who weighs 150 pounds (68 kg) and stands 5’6″ (168 cm) would calculate: (10 × 68) + (6.25 × 168) − (5 × 35) − 161 = 1,394 calories at rest.
That number only covers what your body needs lying in bed all day. To get your actual maintenance calories, multiply it by an activity factor:
- Sedentary (desk job, little or no exercise): multiply by 1.2
- Lightly active (light exercise 1 to 3 days per week): multiply by 1.375
- Moderately active (moderate exercise 3 to 5 days per week): multiply by 1.55
- Very active (hard exercise 6 to 7 days per week): multiply by 1.725
- Super active (intense training or physical job): multiply by 1.9
Using the example above, that 35-year-old woman with a sedentary lifestyle would need about 1,673 calories per day to maintain her weight (1,394 × 1.2). If she exercised moderately a few days a week, her maintenance number jumps to roughly 2,161 calories (1,394 × 1.55). The difference between sedentary and moderately active is nearly 500 calories a day, which illustrates how much regular movement shapes your calorie needs.
Why the Formula Is a Starting Point
These equations give you a useful estimate, not a precise measurement. Several factors can push your real number higher or lower. Muscle tissue burns more calories at rest than fat tissue, so two people at the same weight can have different metabolic rates depending on body composition. The formulas don’t account for this directly.
Your daily movement outside of exercise also matters more than most people realize. Someone who paces while on the phone, takes the stairs, and walks to lunch is burning hundreds of extra calories compared to someone who sits most of the day, even if neither person does formal workouts. This kind of incidental movement is one of the biggest hidden variables in your maintenance number.
Diet composition plays a small but real role too. Because protein costs more energy to digest than carbs or fat, a higher-protein diet slightly increases your total daily burn. The difference isn’t dramatic, but it’s one reason protein-rich diets tend to make weight maintenance easier.
How Age Affects Your Calorie Needs
You’ve probably heard that metabolism slows down as you get older, but the timeline is different from what most people assume. Research published in Science and covered by Harvard Health found that metabolic rate stays remarkably stable between the ages of 20 and 60, after adjusting for changes in body size and composition. The formula includes an age variable that slightly reduces your estimate each year, but the real-world effect between ages 20 and 60 is modest.
What actually changes in middle age is body composition: people tend to lose muscle and gain fat gradually, which lowers metabolic rate indirectly. The fix is staying physically active and maintaining muscle, not simply accepting that you need to eat less every year. After 60, metabolic rate does decline more noticeably, making activity and muscle preservation even more important.
Metabolic Adaptation After Weight Loss
If you’ve recently lost a significant amount of weight, your maintenance calories are likely lower than the formula predicts. This is called metabolic adaptation. Your body responds to weight loss by becoming more energy-efficient, burning fewer calories than expected for someone your new size. Research from the University of Alabama at Birmingham found that women who lost about 16 percent of their body weight experienced measurable metabolic adaptation, and those with greater adaptation took longer to reach their goals.
The larger the weight loss, the stronger this effect tends to be. If you’ve lost 30 or more pounds, your actual maintenance number could be 100 to 300 calories below what any calculator tells you. This doesn’t last forever, but it can persist for months or even years. The practical takeaway: if you’re maintaining after major weight loss and the formula says you should be fine at 2,000 calories but you’re slowly gaining, you’re not doing anything wrong. Your body is simply running more efficiently than the math assumes.
Finding Your Real Number
The best way to pin down your personal maintenance calories is to treat the formula as a starting point and then track what actually happens. Eat at your calculated level for two to three weeks while weighing yourself under consistent conditions (same time of day, same clothing). Your weight will fluctuate day to day from water, food volume, and hormonal shifts, so look at the weekly trend rather than any single reading.
If your weight stays stable over two to three weeks, you’ve found your maintenance range. If you’re slowly gaining, reduce by 100 to 200 calories and reassess. If you’re losing, add a similar amount. This trial-and-error process sounds tedious, but it only takes a few weeks to dial in, and it accounts for all the individual variables that no equation can capture.
Keep in mind that your maintenance calories aren’t a fixed number. They shift with the seasons, your activity patterns, stress levels, sleep quality, and changes in body composition. Think of maintenance as a range rather than a single target, typically a window of about 100 to 200 calories in either direction on any given day.