Your maintenance calories are the number of calories you burn in a full day, accounting for everything from breathing to exercise. For most adults, this falls somewhere between 1,800 and 3,000 calories per day, depending on size, muscle mass, age, and how active you are. You can get a solid estimate using a two-step process: first calculate your resting metabolic rate with a proven formula, then multiply it by a number that reflects your activity level.
Step 1: Calculate Your Resting Metabolic Rate
Your resting metabolic rate (RMR) is the energy your body uses just to keep you alive: pumping blood, maintaining body temperature, running your brain. It accounts for roughly 60 to 70 percent of the calories you burn each day. The most reliable formula for estimating it is the Mifflin-St Jeor equation, which a systematic review in the Journal of the American Dietetic Association found predicted RMR within 10% of lab-measured values in more people than any competing formula, with the narrowest error range.
Here’s the math:
- 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
If you’re more comfortable with 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. For example, a 35-year-old man who weighs 180 pounds (81.8 kg) and stands 5’10” (177.8 cm) would calculate: (10 × 81.8) + (6.25 × 177.8) − (5 × 35) + 5 = 1,754 calories per day at rest.
Step 2: Factor In Your Activity Level
Your RMR only captures what you burn at rest. To get your total daily energy expenditure, which is your actual maintenance number, multiply it by an activity factor:
- Sedentary (desk job, little to 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
Using the example above, if that 35-year-old man exercises moderately three to four times a week, his estimated maintenance calories would be 1,754 × 1.55 = about 2,719 calories per day. Most people overestimate their activity level. If you work out three or four times a week but sit at a desk the rest of the time, “lightly active” is often more accurate than “moderately active.” Start conservative and adjust from there.
When Body Composition Changes the Math
The Mifflin-St Jeor equation uses total body weight, which means it doesn’t distinguish between muscle and fat. This matters because lean tissue burns significantly more energy at rest than fat tissue does. Two people who weigh the same but carry very different amounts of muscle can have maintenance calorie needs that are hundreds of calories apart.
If you know your body fat percentage (from a DEXA scan, skinfold calipers, or even a rough estimate), the Katch-McArdle formula accounts for this directly. It calculates RMR using only your lean body mass:
RMR = 370 + (21.6 × lean body mass in kg)
To find your lean mass, take your total weight in kilograms and subtract your fat mass. If you weigh 82 kg at 20% body fat, your lean mass is about 65.6 kg, giving you an RMR of 370 + (21.6 × 65.6) = 1,787 calories. You’d then apply the same activity multipliers from Step 2. This formula is particularly useful for people who are very muscular or carry significantly more body fat than average, since weight-only formulas tend to underestimate for the first group and overestimate for the second.
Why Your Estimate Is a Starting Point, Not a Final Answer
No formula perfectly captures what’s happening inside your body. Research comparing predicted energy expenditure to lab measurements (using indirect calorimetry, which measures the actual gases you breathe in and out) has found that individual accuracy is low. Fewer than half of predictions land within 10% of the true value, and the margin of error can be 230 to 317 calories per day. Across different equations, systematic bias ranges from underestimating by 6% to overestimating by 18%.
Several factors explain why the math doesn’t perfectly match reality. Genetics play a role: some people simply run hotter or cooler metabolically. Your gut microbiome, hormonal profile, sleep quality, and stress levels all nudge the number up or down in ways no equation captures. Even what you eat changes the equation slightly. Your body spends energy digesting food (called the thermic effect of food), and that cost varies by macronutrient. Protein costs the most to process, increasing your metabolic rate by 15 to 30% of the protein calories consumed. Carbohydrates cost 5 to 10%, and fats cost 0 to 3%. Someone eating a high-protein diet genuinely burns more calories through digestion alone than someone eating the same number of calories mostly from fat.
How Dieting History Affects Your Number
If you’ve recently been eating in a calorie deficit, your maintenance calories are likely lower than any formula will predict. This is because of a phenomenon called adaptive thermogenesis: your body reduces its energy expenditure beyond what the loss of body weight alone would explain. In one study of overweight adults on a calorie-restricted diet, metabolic rate dropped by an average of 178 calories per day within just the first week, and that reduction stayed remarkably consistent throughout six weeks of dieting and even after the diet ended.
This metabolic slowdown is meaningful. An extra 100-calorie-per-day drop in metabolic rate during the first week of a diet was associated with about 2 kg (4.4 lbs) less weight loss over six weeks. For someone coming out of a prolonged diet, true maintenance calories may be noticeably below what a formula suggests. The effect does reverse over time as you return to eating more, but it can take weeks to months. This is one reason people regain weight quickly after a diet: they return to a calorie level that was maintenance before, but their metabolism hasn’t caught up yet.
The Practical Way to Dial In Your Number
The most accurate approach combines a formula-based estimate with real-world tracking. Start by calculating your number using the steps above, then eat at that level for two to three weeks while weighing yourself daily under consistent conditions (same time, same clothing, after using the bathroom). Average your weight each week rather than comparing individual days, since daily weight fluctuates by 1 to 4 pounds from water, sodium, and digestion.
If your weekly average stays stable over two to three weeks, you’ve found your maintenance calories. If you’re slowly gaining, reduce by 100 to 150 calories and observe again. If you’re slowly losing, add the same amount. This iterative process sounds tedious, but it typically takes three to four weeks to land on a reliable number, and it accounts for all the individual variables that no equation can capture.
Keep in mind that maintenance calories aren’t fixed. They shift with the seasons, with changes in your exercise routine, with aging, and with fluctuations in body composition. Rechecking every few months, or whenever your routine changes significantly, keeps the number useful.