Most adults need somewhere between 1,600 and 3,000 calories per day to maintain their current weight, with the exact number depending on your age, sex, height, weight, and how physically active you are. That’s a wide range, which is why a personalized estimate matters more than any single guideline. The good news is that calculating your number takes about two minutes with a simple formula.
How to Calculate Your Number
Your maintenance calories come down to two things: how many calories your body burns just to keep you alive (your resting metabolic rate), and how many additional calories you burn through movement. The most reliable way to estimate the first part is the Mifflin-St Jeor equation. A systematic review in the Journal of the American Dietetic Association compared the most commonly used formulas and found that Mifflin-St Jeor predicted resting metabolic rate within 10% of the measured value in more people than any other equation, with the narrowest error range.
Here’s how it works:
- For men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- For women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
If you prefer pounds and inches, convert first: divide your weight in pounds by 2.2 to get kilograms, and multiply your height in inches by 2.54 to get centimeters. The result gives you the calories your body burns at complete rest. To get your actual maintenance number, you need to account for physical activity.
Activity Level Changes Everything
Once you have your resting metabolic rate, multiply it by an activity factor. The Food and Agriculture Organization of the United Nations classifies activity levels into three broad categories:
- Sedentary or lightly active (multiply by 1.4 to 1.69): Office work, light walking, mostly sitting throughout the day.
- Moderately active (multiply by 1.7 to 1.99): Regular exercise several days a week, or a job that involves standing and moving for hours.
- Vigorously active (multiply by 2.0 to 2.4): Heavy physical labor, training for endurance sports, or multiple intense workouts per day. Values above 2.4 are difficult to sustain over the long term.
A 35-year-old woman who is 5’5″ and 150 pounds would have a resting metabolic rate of roughly 1,400 calories. If she’s moderately active, her maintenance calories land around 2,380 to 2,800. If she’s mostly sedentary, that drops to about 1,960 to 2,370. The difference between sitting at a desk and exercising regularly can easily be 500 or more calories per day.
Most people overestimate how active they are. If you work out three or four times a week but spend the rest of your day at a computer, you’re closer to the low end of “moderately active” or the high end of “sedentary.” Be honest with yourself here, because this multiplier has more influence on your final number than almost any other variable.
Why Your Body Burns What It Burns
Your resting metabolic rate accounts for roughly 60 to 70% of the calories you burn each day. That energy goes toward breathing, circulating blood, maintaining body temperature, and keeping your organs running. Your brain, liver, kidneys, and heart are the real calorie burners: pound for pound, these organs use 15 to 40 times more energy than muscle tissue and 50 to 100 times more than fat tissue.
Muscle does matter, though. Each pound of muscle burns roughly 4.5 to 7 calories per day at rest. Each pound of fat burns considerably less. That might sound small, but it adds up. Someone carrying 20 extra pounds of muscle compared to another person of the same weight burns an additional 90 to 140 calories per day just existing. This is one reason why two people of identical height and weight can have noticeably different calorie needs.
Your body also burns calories digesting food, a process called the thermic effect of food. Not all nutrients cost the same energy to process. Protein increases your metabolic rate by 15 to 30% of the calories consumed. Carbohydrates cost 5 to 10%, and fats cost 0 to 3%. This doesn’t mean you should eat only protein, but it does explain why higher-protein diets tend to make weight maintenance slightly easier.
What Changes After Weight Loss
If you’ve recently lost weight, your maintenance calories are lower than the formula predicts. When you lose weight, you lose some muscle along with fat. Since muscle burns more calories than fat, your metabolism slows. Your body also becomes more efficient at using energy, a survival mechanism that worked well for our ancestors but makes modern weight maintenance frustrating.
This means the calorie level that helped you lose weight eventually becomes your new maintenance level. You burn fewer calories at a lighter weight, both because there’s less of you to fuel and because your body has adapted to conserve energy. If your weight loss stalls and you’re eating the same amount that previously produced results, this metabolic shift is the most likely explanation. Recalculating your maintenance calories at your new weight, and being realistic about your current activity level, gives you a more accurate target.
How to Find Your Real Number
Formulas give you a starting point, not a final answer. The Mifflin-St Jeor equation is the best available estimate, but “within 10%” still means your true number could be 150 to 250 calories higher or lower than what the math says. Individual differences in genetics, gut bacteria, hormones, and daily movement patterns all create variation that no equation captures perfectly.
The most reliable method is to track what you eat and what you weigh over two to three weeks. Weigh yourself at the same time each day (morning, after using the bathroom), take a weekly average, and compare week to week. If your average weight stays stable, you’ve found your maintenance calories. If it drifts up, you’re eating above maintenance. If it drifts down, you’re below.
Don’t rely on your smartwatch to do this work for you. Wrist-worn fitness trackers have estimated error rates of 30 to 80% for calories burned, according to research from Harvard’s School of Engineering. They’re useful for comparing one day’s activity to another, but the absolute calorie number on the screen is often far from reality. Your own weight trend over time is a much more trustworthy signal than any device.
Practical Tips for Staying on Target
Once you know your maintenance number, consistency matters more than precision. You don’t need to hit the exact number every day. What matters is that your weekly average lands close to the target. Eating 200 calories over on Monday and 200 under on Wednesday balances out.
Protein deserves extra attention. Because it costs your body more energy to digest and helps preserve muscle mass, keeping protein intake relatively high (around 25 to 30% of your total calories) supports a healthier metabolic rate over time. This is especially important if you’re maintaining after weight loss, since preserving muscle offsets some of the metabolic slowdown that comes with a lighter body.
Recalculate every 10 to 15 pounds of weight change, or whenever your activity level shifts significantly. A new job that keeps you on your feet, a running habit you picked up, or a season where you’re less active all change the equation. Your maintenance calories aren’t a fixed number. They’re a moving target that shifts with your body and your life.