Your daily calorie needs depend on three things: your body’s baseline metabolism, how active you are, and whether you’re trying to lose, gain, or maintain weight. Most adults need somewhere between 1,600 and 3,000 calories per day, but that range is so wide it’s almost useless. To get a number that actually applies to you, you need to work through a few simple steps.
Start With Your Basal Metabolic Rate
Your basal metabolic rate (BMR) is the number of calories your body burns just keeping you alive: breathing, circulating blood, regulating temperature, repairing cells. For most people, this accounts for about 60 to 70 percent of total daily calorie burn. It’s the foundation of your calorie target, and everything else builds on top of it.
The most widely used formula for estimating BMR is the Mifflin-St Jeor equation. You need 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
So a 35-year-old woman who weighs 70 kg (154 lbs) and stands 165 cm (5’5″) would calculate: (10 × 70) + (6.25 × 165) – (5 × 35) – 161 = 1,396 calories per day at rest. That’s before any movement at all.
If you know your body fat percentage (from a DEXA scan or reliable body composition test), you can use the Katch-McArdle formula instead. It factors in lean body mass, which makes it more accurate for people who carry significantly more muscle than average: BMR = 370 + (21.6 × lean mass in kg). Standard equations use total body weight, so they can underestimate calorie needs in muscular people and overestimate them in people with higher body fat percentages.
Factor In Your Activity Level
Your BMR tells you what your body burns at complete rest. To estimate what you actually burn in a full day, you multiply it by an activity factor. This gives you your total daily energy expenditure (TDEE), which is the number you’ll use to set your calorie target.
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (exercise 1-3 days/week): BMR × 1.375
- Moderately active (exercise 3-5 days/week): BMR × 1.55
- Very active (hard exercise 6-7 days/week): BMR × 1.725
- Extremely active (physical job + heavy training): BMR × 1.9
Using the example above, that 35-year-old woman with a BMR of 1,396 who exercises three times a week would multiply by 1.55, landing at roughly 2,164 calories per day to maintain her current weight.
The biggest mistake people make here is overestimating their activity level. If you work out for an hour but spend the other 15 waking hours sitting, you’re probably closer to “lightly active” than “moderately active.” Be honest with yourself at this step, because the difference between multipliers can mean 200 to 400 calories per day.
Why Daily Movement Matters More Than You Think
Formal exercise typically burns a relatively small portion of your total daily calories. A much larger and more variable contributor is all the non-exercise movement you do throughout the day: walking to the kitchen, fidgeting, standing, doing chores, taking the stairs. Researchers call this non-exercise activity thermogenesis, or NEAT. According to research from the Mayo Clinic, NEAT can vary by up to 2,000 calories per day between two people of similar size. That’s an enormous gap, and it largely explains why some people seem to eat freely without gaining weight while others gain on relatively modest portions.
This also means that small changes in your daily habits, like standing more, walking after meals, or taking movement breaks, can meaningfully shift your calorie balance without any structured exercise.
Adjust for Your Goal
Once you have your TDEE, you adjust it based on what you’re trying to accomplish.
For Weight Loss
Cutting about 500 calories per day from your TDEE typically leads to roughly half a pound to one pound of weight loss per week. The old rule that 3,500 calories equals one pound of fat is a useful approximation, but real-world results vary depending on your starting weight, body composition, and how long you’ve been dieting. Larger deficits produce faster initial losses, but they also increase muscle loss, trigger stronger hunger signals, and are harder to sustain. A moderate deficit of 300 to 500 calories is the range most people can stick with long-term without feeling miserable.
There’s also a practical floor to be aware of. Going below roughly 1,200 calories per day for women or 1,500 for men makes it very difficult to get adequate nutrition, and the fatigue and hunger that come with extreme restriction usually lead to cycles of restriction and overeating.
For Muscle Gain
Building muscle requires a calorie surplus, but the body can only synthesize new muscle tissue at a limited rate. The current consensus is that a surplus of 300 to 500 calories per day maximizes lean muscle growth while minimizing fat gain. Going much higher doesn’t speed up muscle building; it just adds more body fat alongside whatever muscle you’re gaining. Pairing this surplus with adequate protein and a progressive resistance training program is what makes the surplus productive rather than just extra stored energy.
For Maintenance
If you’re happy with your current weight and body composition, your TDEE is your target. In practice, most people don’t need to hit the exact number daily. Your body averages things out over days and weeks. Consistently eating within 100 to 200 calories of your TDEE in either direction will keep your weight stable.
What Your Food Does After You Eat It
Not all calories are processed identically by your body. Digesting food itself burns calories, a process called the thermic effect of food. Protein costs the most energy to digest, increasing your metabolic rate by 15 to 30 percent of the calories consumed. Carbohydrates raise it by 5 to 10 percent, and fats by just 0 to 3 percent. This doesn’t mean you should eat only protein, but it does help explain why higher-protein diets tend to support weight management: you’re effectively absorbing fewer net calories from protein, and protein keeps you fuller longer.
How Age Affects Your Calorie Needs
A widespread belief holds that metabolism slows steadily starting in your 20s or 30s. A large 2021 study published in Science found something different. Metabolic rate, adjusted for body size and composition, stays remarkably stable from age 20 all the way to about 60. The weight gain most people experience in their 30s and 40s is more likely driven by changes in activity levels, eating habits, and muscle mass than by an inherent metabolic slowdown.
After 60, metabolism does begin to decline at about 0.7 percent per year. By age 90, adjusted energy expenditure is roughly 26 percent below that of middle-aged adults. So if you’re under 60, your metabolism probably isn’t the problem. If you’re over 60, a gradual reduction in calorie intake or increase in activity can help offset the shift.
Why Fitness Trackers Are a Rough Guide
Wearable devices are popular tools for estimating daily calorie burn, but their accuracy for energy expenditure is poor. A Stanford study testing seven popular fitness trackers found that even the most accurate device was off by an average of 27 percent, and the least accurate missed by 93 percent. These same devices measured heart rate within 5 percent error, so they’re useful for tracking workout intensity. But the calorie number on your wrist should be treated as a loose estimate, not a precise measurement.
If you’re using a tracker, it’s better to rely on the trend over weeks (are you consistently hitting your goals?) rather than trusting the daily calorie number as gospel.
Putting Your Number Into Practice
Calculating your calorie target is the starting point, not the finish line. Any formula gives you an estimate based on population averages, and your actual metabolism could be somewhat higher or lower. The most reliable approach is to eat at your calculated target for two to three weeks, track your weight, and see what happens. If your weight stays stable, you’ve found your maintenance level. If it drifts up or down, adjust by 100 to 200 calories and reassess.
You don’t need to track calories forever. Many people use the calculation phase to build an intuitive sense of portion sizes and meal composition, then transition to eating by habit once they understand what a day’s worth of food looks like for their body. The goal is a number you can use, not a number that uses you.