To calculate your daily calorie intake, you need two numbers: your basal metabolic rate (BMR), which is the energy your body burns at complete rest, and a multiplier based on how active you are. Together, these give you your total daily energy expenditure, or TDEE. That number is your starting point for maintaining, losing, or gaining weight.
Step 1: Calculate Your BMR
Your BMR represents the calories your body needs just to keep you alive: breathing, circulating blood, maintaining body temperature, and running your organs. It typically accounts for 60 to 70% of all the calories you burn in a day. The remaining energy goes toward physical activity and digesting food (which burns roughly 10% of what you eat).
The most widely recommended formula is the Mifflin-St Jeor equation. The Academy of Nutrition and Dietetics rates it as the most accurate option for estimating metabolic rate, including in people who are overweight or obese. It predicted resting metabolic rate within 10% of the actual measured value in 70% of individuals studied. You’ll need your weight in kilograms, height in centimeters, and age in years.
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
To convert: divide your weight in pounds by 2.2 for kilograms, and multiply your height in inches by 2.54 for centimeters.
A Worked Example
Say you’re a 35-year-old woman who weighs 155 pounds (70.5 kg) and stands 5’6″ (167.6 cm). Plugging into the formula: (10 × 70.5) + (6.25 × 167.6) − (5 × 35) − 161 = 705 + 1,047.5 − 175 − 161 = 1,416 calories. That’s your BMR, the bare minimum your body burns lying in bed all day.
Step 2: Factor In Your Activity Level
Your BMR alone isn’t useful for planning meals because it ignores everything you do once you get out of bed. To get your TDEE, multiply your BMR by an activity factor:
- Sedentary (desk job, little or no exercise): BMR × 1.2
- Lightly active (light exercise 1 to 3 days per week): BMR × 1.375
- Moderately active (moderate exercise 3 to 5 days per week): BMR × 1.55
- Very active (hard exercise 6 to 7 days per week): BMR × 1.725
- Extra active (very intense daily training or a physical job): BMR × 1.9
Using the example above, that 35-year-old woman with a BMR of 1,416 who exercises moderately three to four days a week would multiply 1,416 × 1.55, landing at roughly 2,195 calories per day. That’s her estimated maintenance intake, the amount that should keep her weight stable.
Why Activity Multipliers Are Only Estimates
The trickiest part of this calculation is honestly assessing how active you are. One major variable is non-exercise activity thermogenesis, or NEAT. This is all the movement you do that isn’t formal exercise: walking around your office, fidgeting, cooking, cleaning, even standing instead of sitting. According to research from the Mayo Clinic, NEAT can vary by up to 2,000 calories per day between two people of similar size. Someone with an active job who’s on their feet all day burns dramatically more than someone who sits for eight hours, even if neither of them sets foot in a gym.
This means the activity multiplier is your best guess, not a precise measurement. If you choose “moderately active” but spend most of your non-exercise hours sitting, you may be overestimating. Be conservative with your selection and adjust based on real-world results over two to four weeks.
An Alternative for Muscular Body Types
The Mifflin-St Jeor equation uses total body weight, which works well for most people. But if you carry significantly more muscle than average (or significantly more body fat), a formula that accounts for body composition will be more accurate. Lean body tissue is far more metabolically active than fat tissue, so two people at the same weight can have very different calorie needs depending on how much of that weight is muscle.
The Katch-McArdle formula handles this by using lean body mass instead of total weight: BMR = 370 + (21.6 × lean body mass in kg). You’ll need to know your body fat percentage to use it. If you’ve had a DEXA scan, hydrostatic weighing, or even a reliable estimate from skinfold calipers, subtract your fat mass from your total weight to get lean mass, then plug it in.
Adjusting for Weight Loss or Gain
Your TDEE is your maintenance number. To change your weight, you adjust from there.
For weight loss, the NHS recommends reducing your daily intake by about 600 calories below your maintenance level. For reference, this would bring the average man from roughly 2,500 calories down to 1,900 and the average woman from 2,000 down to 1,400. A deficit in this range typically produces a loss of about one pound per week, which is a pace that’s sustainable and less likely to cause muscle loss or metabolic slowdown.
For muscle gain, a smaller surplus is typical. Adding 250 to 500 calories above your TDEE provides enough extra energy to support muscle growth when combined with resistance training, without excessive fat gain.
How Calorie Needs Change With Age and Sex
Your calorie needs aren’t fixed. They shift meaningfully across your lifetime. The Dietary Guidelines for Americans lay out estimated needs by age, sex, and activity level. A few highlights show the pattern:
- Active men in their late teens peak at around 3,200 calories per day
- Active men ages 36 to 40 need roughly 2,800
- Sedentary men over 61 drop to about 2,000
- Active women ages 19 to 25 need around 2,400
- Sedentary women over 51 need roughly 1,600
The decline happens because you lose muscle mass gradually as you age, and muscle is the most metabolically expensive tissue in your body. This is one reason strength training becomes increasingly important over time: it helps preserve the tissue that keeps your metabolic rate higher.
Pregnancy and breastfeeding also shift needs. Calorie needs don’t increase at all during the first trimester, rise by about 340 calories in the second trimester, and by roughly 450 in the third. During breastfeeding, needs go up by 330 to 400 calories per day above pre-pregnancy levels.
Why Your Tracking Will Never Be Perfect
Even with a solid TDEE estimate, the calorie counts you log in a food diary or app carry their own margin of error. Research from the National Cancer Institute found that people consistently underreport how much they eat, especially those with higher intakes. People who eat less than average tend to slightly overreport. No self-report method, whether it’s a food diary, a 24-hour recall, or a questionnaire, is truly unbiased. Food labels themselves are allowed to be off by up to 20% in the U.S.
This doesn’t mean tracking is useless. It means you should treat your calculated number as a starting point, not a verdict. Weigh yourself under consistent conditions (same time of day, same clothing) once or twice a week, and track the trend over two to four weeks. If your weight is stable, you’ve found your true maintenance. If it’s drifting up or down, adjust by 100 to 200 calories and reassess. The math gets you in the right neighborhood. Your body’s response tells you the exact address.