Your maintenance calories are the total number of calories your body burns in a day, including everything from breathing and digesting food to walking and exercising. Most adults fall somewhere between 1,800 and 3,000 calories per day, but the exact number depends on your size, body composition, age, and how active you are. There are several reliable ways to estimate yours, and a simple method to confirm the estimate using real-world data.
Start With a Predictive Equation
The most widely recommended starting point is the Mifflin-St Jeor equation, which estimates your resting metabolic rate (the calories your body burns just to keep you alive at rest). The formulas use your 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: divide your weight in pounds by 2.2 for kilograms, and multiply your height in inches by 2.54 for centimeters. The number you get is your resting metabolic rate in calories per day.
This equation tends to overestimate slightly. When researchers compared it against indirect calorimetry (the gold standard, where you breathe into a machine that measures your actual oxygen consumption), the Mifflin-St Jeor equation predicted about 1,607 calories per day on average in a group whose actual measured rate was 1,451 calories. That’s roughly a 10% overshoot, which is worth keeping in mind. It’s a starting point, not a final answer.
Multiply by Your Activity Level
Your resting metabolic rate only accounts for the energy your body uses lying still. To get total daily energy expenditure (your actual maintenance calories), you multiply that number by a physical activity level factor. The Food and Agriculture Organization of the United Nations classifies these into three tiers:
- Sedentary or light activity (desk job, minimal exercise): multiply by 1.4 to 1.69
- Moderately active (regular exercise, on your feet part of the day): multiply by 1.7 to 1.99
- Vigorously active (intense daily training, physical labor): multiply by 2.0 to 2.4
Values above 2.4 are difficult to sustain over long periods. Most people with a typical office job who exercise three to four times per week fall somewhere around 1.5 to 1.7. A common mistake is overestimating activity level, so if you’re unsure, start at the lower end of the range that seems right for you.
When Body Composition Matters More
Standard equations use total body weight, but muscle tissue burns significantly more energy at rest than fat tissue does. If you carry more muscle than the average person at your weight, or conversely if you have a higher body fat percentage, a weight-based equation can miss the mark. The Katch-McArdle formula addresses this by using lean body mass instead:
BMR = 370 + (21.6 × lean body mass in kg)
You need a reasonable estimate of your body fat percentage to use this. If you know yours from a DEXA scan, body fat calipers, or even a rough visual estimate, subtract your fat mass from your total weight to get lean mass. For someone who is notably muscular or notably high in body fat, this formula often gives a more useful baseline than Mifflin-St Jeor.
Why Wearable Devices Are Unreliable
Smartwatches and fitness trackers display a “calories burned” number that feels precise but often isn’t. Research from Harvard’s School of Engineering found that estimated error rates for wearable calorie tracking range from 30 to 80%. That means a watch telling you that you burned 500 calories during a workout could be off by 150 to 400 calories in either direction. Wearables are useful for tracking trends over time (did you move more this week than last?), but the absolute calorie number is too unreliable to use as your maintenance target without verification.
The Real-World Tracking Method
The most accurate way to find your maintenance calories doesn’t require any equation at all. It requires patience and a food scale. Here’s how it works:
Track everything you eat for two to three weeks while weighing yourself daily under consistent conditions (same time of day, same clothing or none, after using the bathroom). Calculate your average weekly calorie intake and your average weekly weight. If your weight stays stable across two or more weeks, your average intake during that period is very close to your true maintenance calories.
Daily weight fluctuates due to water retention, sodium intake, and digestive contents. That’s why you need at least two weeks and should look at weekly averages rather than day-to-day changes. A stable trend line over 14 to 21 days is strong evidence you’ve found the right number. If your weight is trending down, your intake is below maintenance. If it’s trending up, you’re above it. Adjust by 100 to 200 calories and track for another week or two.
What Your Diet Is Made of Also Matters
Not all calories cost the same amount of energy to digest. Your body uses calories just to break down and absorb food, a process called the thermic effect of food. Protein costs the most: your body spends 15 to 30% of protein calories just processing them. Carbohydrates cost 5 to 10%, and fats cost 0 to 3%. This means that two diets with identical calorie counts but different ratios of protein, carbs, and fat will leave your body with slightly different amounts of usable energy. A higher-protein diet effectively raises your metabolic rate modestly compared to a diet built mostly around fats and refined carbs.
This doesn’t mean you need to restructure your entire diet around protein, but it does explain why some people find they can eat slightly more total calories without gaining weight when protein makes up a larger share of their intake.
Maintenance Calories Change Over Time
Your maintenance number is not fixed. It shifts as your weight, age, activity level, and body composition change. One important mechanism to understand is metabolic adaptation: after significant weight loss, your body often burns fewer calories than equations would predict for your new weight. Imagine someone who weighs 220 pounds and maintains on 2,500 calories. After losing 22 pounds, you’d expect their needs to drop to around 2,200 calories based on the weight change alone. But when measured in a metabolic chamber, their actual expenditure might only be 2,000 calories. That 200-calorie gap is metabolic adaptation.
The reassuring finding is that this adaptation doesn’t appear to predict weight regain. Research published in 2022 in the journal Obesity found that people with greater metabolic adaptation simply took longer to reach their weight-loss goals, but they didn’t necessarily regain more weight afterward. A related 2023 study in the American Journal of Clinical Nutrition found that metabolic adaptation is linked to increased appetite after weight loss, but again, not to actual regain. The practical takeaway: if you’ve lost a significant amount of weight, your true maintenance calories are likely lower than any calculator tells you, and the tracking method described above becomes especially important.
Signs Your Estimate Is Too Low
If you’ve set a calorie target and are consistently eating below your actual maintenance level, your body will send signals. Persistent fatigue that doesn’t improve with sleep is one of the earliest signs. Poor sleep quality, difficulty falling asleep, and frequent waking are also common when calorie intake is chronically too low.
Other red flags include feeling cold when others around you are comfortable (your body lowers its core temperature to conserve energy), prolonged periods of irritability or low mood, and for women, irregular or missed periods. These hormonal disruptions happen because the reproductive system is one of the first things your body deprioritizes when energy is scarce. If you’re experiencing several of these symptoms, your maintenance estimate likely needs to come up, and the tracking method with gradual 100 to 200 calorie increases is the safest way to find the right level.
Putting It All Together
Use an equation as your starting estimate. The Mifflin-St Jeor formula with an honest activity multiplier will get most people within a few hundred calories of their true number. If you know your body fat percentage, the Katch-McArdle formula may be more precise. Then validate that estimate by tracking your intake and weight for two to three weeks. Adjust based on what the scale trend tells you, not what the equation says. Your maintenance calories are ultimately an empirical number, something you discover through observation rather than calculation alone.