Your daily caloric needs depend on four things: your age, sex, body size, and how active you are. The most reliable way to estimate them is a two-step process: first calculate your basal metabolic rate (BMR), the calories your body burns just to stay alive, then multiply by an activity factor that accounts for everything else you do in a day. For most adults, the result lands somewhere between 1,600 and 3,000 calories per day.
Step 1: Calculate Your Basal Metabolic Rate
Your BMR is the energy your body uses at complete rest: breathing, circulating blood, maintaining body temperature, and keeping organs running. It typically accounts for 60 to 70 percent of the calories you burn each day. The Mifflin-St Jeor equation is the most widely recommended formula for estimating it, shown in a systematic review published in the Journal of the American Dietetic Association to predict resting metabolic rate within 10 percent of lab-measured values more often than any competing equation.
The formula uses your weight in kilograms, height in centimeters, and age in years:
- For men: (10 × weight) + (6.25 × height) – (5 × age) + 5
- For 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. So 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 = 680 + 1,050 – 175 – 161 = 1,394 calories per day at rest.
Keep in mind that even the best formula is an estimate. The Mifflin-St Jeor equation has a narrower error range than older formulas like the Harris-Benedict equation, but individual variation still exists, particularly across different age groups and ethnic backgrounds. Treat the number as a solid starting point, not a precise measurement.
If You Know Your Body Fat Percentage
People with significantly more or less muscle than average may get a more accurate estimate from the Katch-McArdle formula, which uses lean body mass instead of total weight. This matters because muscle tissue burns more calories at rest than fat tissue does. The formula is simple: 370 + (21.6 × lean body mass in kg).
To find your lean body mass, subtract your body fat from your total weight. If you weigh 80 kg and have 10 percent body fat, your fat mass is 8 kg, leaving 72 kg of lean mass. Plugging that in: 370 + (21.6 × 72) = 1,925 calories per day. You’ll need a reasonable body fat estimate for this to be useful. Calipers, body composition scales, or a DEXA scan can all provide one, though accuracy varies by method.
Step 2: Factor In Your Activity Level
Your BMR only covers survival functions. To get your total daily energy expenditure (TDEE), the actual number of calories you need, you multiply your BMR by an activity factor:
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (light exercise 1-3 days/week): BMR × 1.375
- Moderately active (moderate exercise 3-5 days/week): BMR × 1.55
- Very active (hard exercise 6-7 days/week): BMR × 1.725
- Extremely active (physical job plus intense training): BMR × 1.9
Using the example above, that 35-year-old woman with a BMR of 1,394 who exercises moderately a few times a week would multiply 1,394 × 1.55, giving her a TDEE of roughly 2,161 calories per day. That’s her maintenance number, the amount she’d eat to stay at her current weight.
What Makes Up Your Total Calorie Burn
Your TDEE isn’t just BMR plus exercise. Three components contribute to it, and understanding them helps explain why two people of the same size can have very different calorie needs.
The first is your BMR, the biggest slice. The second is the thermic effect of food: your body uses energy to digest what you eat. This typically accounts for about 10 percent of your caloric intake. The cost varies by macronutrient. Protein takes the most energy to process, increasing your metabolic rate by 15 to 30 percent of the calories in that protein. Carbohydrates cost 5 to 10 percent, and fats just 0 to 3 percent. This is one reason higher-protein diets can slightly boost overall calorie burn.
The third component, and the most variable, is physical activity, which includes both structured exercise and everything else you do while moving: walking around the office, fidgeting, cooking, carrying groceries. This non-exercise movement can account for enormous differences between people. Research from the Obesity Medicine Association shows that the gap between a very sedentary person and a highly active one of similar body size can reach up to 2,000 calories per day, driven largely by occupation and lifestyle habits. The average person with a desk job burns about 140 fewer calories per day through work-related movement than workers did in 1960.
Quick Reference: USDA Calorie Estimates
If you want a ballpark without doing any math, the Dietary Guidelines for Americans provides estimated calorie ranges by age, sex, and general activity level. These are based on reference body sizes, so they won’t be as personalized as the formula approach, but they’re useful as a sanity check.
For adult men, the range runs from about 2,400 to 3,000 calories between ages 21 and 35 (sedentary to active), gradually declining to 2,000 to 2,400 by age 76 and older. For adult women, the range is 1,800 to 2,400 calories in the late 20s, tapering to 1,600 to 2,000 by the mid-60s. “Sedentary” in these guidelines means only the movement of basic daily living. “Active” means the equivalent of walking more than 3 miles per day on top of your normal routine.
Adjusting for Weight Loss or Gain
Once you have your TDEE, you adjust based on your goal. To lose weight, you eat below that number. To gain weight, you eat above it. Maintenance means hitting it roughly on target.
A common starting point for weight loss is a deficit of about 500 calories per day, which typically produces a loss of half a pound to one pound per week. That rate varies depending on your starting weight, sex, and activity level, but it’s a widely used benchmark from the Mayo Clinic and most nutrition guidelines. Going much below your BMR for extended periods is generally counterproductive, because your body has ways of pushing back.
One of those pushback mechanisms is metabolic adaptation. When you restrict calories for more than a few days, your body reduces its energy expenditure beyond what you’d expect from weight loss alone. Research on overweight adults found that after just one week of caloric restriction, this adaptive response averaged about 178 calories per day, and it remained relatively stable throughout the dieting period and even after it ended. This means the deficit you calculated on paper may shrink over time, which is one reason weight loss often slows after the first few weeks.
For muscle gain, a smaller surplus of 200 to 300 calories above maintenance is a common recommendation, paired with resistance training. A larger surplus will speed weight gain, but a greater share of it will be fat rather than muscle.
Why Your Number Will Need Updating
Your caloric needs aren’t static. They shift as your weight changes, as you age, and as your activity patterns evolve. Every 5 to 10 pounds of weight change is a reasonable point to recalculate, because a lighter body burns fewer calories at rest and during movement. Age also chips away at your BMR, at a rate of roughly 5 calories per year built into the Mifflin-St Jeor formula.
The most practical approach is to use your calculated TDEE as a starting point, track your weight for two to three weeks while eating consistently, and then adjust. If your weight is stable, you’ve found your true maintenance. If it’s drifting in a direction you don’t want, shift your intake by 100 to 200 calories and reassess. No formula can capture every individual variable, from genetics to sleep quality to stress hormones, but the math gets you close enough that small real-world adjustments can do the rest.