Most adults need somewhere between 1,600 and 3,000 calories per day, but your specific number depends on your age, sex, height, weight, and how active you are. That’s a wide range, which is why a generic answer isn’t very useful. The better approach is understanding how to calculate your own number based on a few straightforward inputs.
How Your Body Burns Calories
Your body uses energy in three main ways. The biggest share, roughly 60 to 70 percent of your daily burn, goes to keeping you alive: breathing, circulating blood, maintaining body temperature, and running your organs. This is your basal metabolic rate, or BMR. Physical activity accounts for 15 to 30 percent, depending on how much you move. The remaining 5 to 15 percent goes toward digesting food itself, a process called the thermic effect of food.
When all three are added together, you get your total daily energy expenditure (TDEE). Eating roughly that number maintains your weight. Eating below it leads to weight loss. Eating above it leads to weight gain.
Calculating Your Personal Number
The most widely used formula for estimating BMR is the Mifflin-St Jeor equation, which researchers have found to be the most accurate for most people. It works like this:
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
To convert your weight to kilograms, divide pounds by 2.2. For height in centimeters, multiply inches by 2.54. As an example, a 35-year-old woman who is 5’6″ and weighs 150 pounds would calculate: (10 × 68.2) + (6.25 × 167.6) − (5 × 35) − 161, giving a BMR of about 1,396 calories per day.
That number only covers what your body burns at complete rest. To get your TDEE, multiply your BMR by an activity factor:
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (light exercise 1 to 3 days per week): BMR × 1.375
- Moderately active (exercise 3 to 5 days per week): BMR × 1.55
- Very active (hard exercise 6 to 7 days per week): BMR × 1.725
Using the same example, that 35-year-old woman with a moderately active lifestyle would have a TDEE of roughly 2,164 calories. That’s her maintenance number, the amount that keeps her weight stable.
Adjusting for Weight Loss
If your goal is to lose weight, you need to eat fewer calories than your TDEE. A deficit of about 500 calories per day typically produces a loss of half a pound to one pound per week. That pace sounds slow, but it’s the range most likely to preserve muscle and keep the weight off long term.
There are important floors you shouldn’t drop below. Harvard Health recommends that women eat no fewer than 1,200 calories per day and men no fewer than 1,500 calories per day without medical supervision. Going lower than that risks nutrient deficiencies and can trigger your body to slow its metabolism aggressively to compensate.
This metabolic slowdown is real and measurable. When you restrict calories, your body reduces its energy expenditure by more than the loss of body mass alone would predict. Research on overweight adults found this adaptive response kicked in within the first week of dieting, averaging about 178 calories per day less than expected. That decline remained relatively stable throughout the dieting period. It’s one reason why weight loss often stalls after several weeks and why very aggressive calorie cuts tend to backfire.
Adjusting for Muscle Gain
Building muscle requires eating more than your TDEE, but the surplus doesn’t need to be enormous. A clinical trial in healthy young men found that a 10 percent calorie surplus (about 200 to 300 extra calories for most people) wasn’t enough to produce significant gains in body protein mass over six weeks. A 40 percent surplus did produce meaningful muscle growth, about 0.44 kg over the study period, but it also came with a strong correlation to fat gain.
For most people trying to add muscle without excessive fat, a surplus of 250 to 500 calories per day is a practical middle ground. The extra energy gives your body the raw materials it needs for repair and growth after strength training, while limiting how much of the surplus gets stored as fat.
Why Body Composition Matters
Two people who weigh the same can have very different calorie needs based on how much of their weight is muscle versus fat. Muscle tissue burns roughly 4.5 to 7 calories per pound per day at rest. That’s not a huge number on its own, but someone carrying 20 extra pounds of muscle could be burning 90 to 140 more calories daily without doing anything. Over months and years, that difference adds up.
Your organs are actually the biggest metabolic drivers, burning 15 to 40 times more energy per unit of weight than muscle and 50 to 100 times more than fat. You can’t change the size of your liver or kidneys, but this explains why the formula is just an estimate. Individual variation in organ size, genetics, and hormonal status means your real number could be 200 or more calories off from any calculator’s prediction.
What You Eat Changes How Many Calories You Absorb
Not all calories are processed the same way. Your body spends energy breaking down and absorbing food, and that cost varies dramatically by nutrient type. Protein has the highest thermic effect: your body uses 15 to 30 percent of protein calories just to digest it. Carbohydrates cost 5 to 10 percent, and fats cost 0 to 3 percent.
This means that if you eat 200 calories of chicken breast, your body might net only 140 to 170 of those calories after digestion. The same 200 calories from butter would net you closer to 194 to 200. This doesn’t mean you should eat only protein, but it does mean that a higher-protein diet effectively lowers your usable calorie intake without changing the number on your plate. It also helps preserve muscle during a calorie deficit, which keeps your metabolic rate from dropping as much.
Putting It All Together
Start by calculating your BMR using the formula above, then multiply by your activity factor to get your TDEE. If you want to lose weight, subtract 500 calories. If you want to gain muscle, add 250 to 500 calories. Track your weight over two to three weeks and adjust from there, because no formula is perfectly accurate for every individual.
Your calorie needs aren’t static. They shift as you age (the formula subtracts 5 calories for every year), as your activity changes, and as your body composition evolves. Someone who loses 20 pounds will have a lower TDEE than when they started, simply because there’s less body to fuel. Recalculating every 10 to 15 pounds of change, or every few months, keeps your target realistic and prevents the kind of plateau that makes people give up.