logo builtwithscience
ABOUT
Menu
close

Calorie Calculator

A calorie calculator is a tool that estimates how many calories you need to eat each day based on your age, weight, height, gender, activity level and body composition. The Built With Science calorie calculator uses a formula based on the Katch-McArdle equation, which factors in your lean body mass for a more individualized estimate than standard formulas. Whether your goal is fat loss, muscle gain or maintaining your current weight, the calculator below will give you a science-backed starting point.

What is a Calorie Calculator?

A calorie calculator is a tool that estimates your daily energy needs based on your individual stats and activity level. It calculates your Total Daily Energy Expenditure (TDEE), which is the number of calories your body burns in a 24-hour period through basic functions like breathing and digestion, plus any physical activity.

Most calorie calculators use your Basal Metabolic Rate (BMR) as a starting point. Your BMR is the number of calories your body needs just to stay alive at complete rest. The calculator then multiplies your BMR by an activity factor to estimate your TDEE.

Once you know your TDEE, you can adjust your calorie intake up or down depending on whether you want to lose fat, build muscle, or maintain your current weight. If you want a more focused estimate of your maintenance calories before setting those targets, you can also use the TDEE calculator.

Calorie Deficit Calculator

A calorie deficit is when you eat fewer calories than your body burns, forcing it to use stored energy (body fat) for fuel. This is the only way to lose fat, as no diet works without creating a deficit, regardless of what foods you eat or when you eat them.

To use this calculator for fat loss, select your goal and find your deficit calories. A moderate deficit of 300-500 calories below your TDEE typically works best for most people. This creates a sustainable rate of fat loss (about 0.3-0.7% of body weight per week) while preserving muscle mass.

If you're leaner (under 15% body fat for men, under 25% for women), stick to the smaller deficit. If you have more fat to lose, you can handle a larger deficit without as much muscle loss risk.

Maintenance Calorie Calculator

Maintenance calories are the number of calories you need to eat to maintain your current body weight - no gain, no loss. This is essentially your TDEE: the total energy your body uses in a day.

Knowing your maintenance calories matters because every goal runs through them. A calorie deficit for fat loss is defined relative to your maintenance. A calorie surplus for muscle gain is added on top of your maintenance. Even body recomposition - losing fat while building muscle at the same time - typically works by eating at or slightly below maintenance while lifting weights.

This calculator estimates your maintenance calories internally using a Katch-McArdle formula that accounts for your lean body mass, then adjusts that number up or down based on your selected goal.

While the calculator doesn't display your maintenance number directly, it uses it as the foundation for every result it gives you. If you want to estimate your maintenance calories manually, take your current body weight in pounds and multiply by 14-16 depending on your activity level.

Calorie Surplus Calculator

A calorie surplus is when you eat more calories than your body burns, providing extra energy for muscle growth. If your goal is to build muscle as efficiently as possible, you need to be in a surplus. It's very difficult to maximize muscle gain while in a deficit.

To use this calculator for lean bulking, select "build muscle" as your goal. A surplus of 200-300 calories per day is the sweet spot for most people. Going much higher (500+ calories) doesn't build muscle faster - it just adds more body fat.

The exception: if you're a beginner lifter or returning after a long break, you can build muscle in a deficit or at maintenance for the first several months. But once you're past the beginner stage, a controlled surplus becomes necessary to keep making progress.

How Many Calories Should I Eat?

The right calorie intake depends entirely on your goal:

For fat loss: Eat 300-500 calories below your TDEE. The calculator shows options for slow, moderate, and fast weight loss - moderate (about 0.5-0.75% of body weight lost per week) works best for most people. Going too aggressive increases muscle loss and makes the diet harder to stick to.

For maintenance: Eat at your TDEE. This is your baseline. If you're not sure what your goal should be, start here for 2-3 weeks to establish your actual maintenance before making changes.

For muscle gain: Eat 200-300 calories above your TDEE. More isn't better, as a 500+ calorie surplus just adds extra fat without building muscle any faster.

These numbers are estimates. Track your weight for 2-3 weeks and adjust based on results. If you're losing weight faster than expected, add calories. If you're not losing at all, reduce calories. The calculator gives you a starting point, and your body gives you the feedback to dial it in.

Once your calorie target is set, you can also calculate your daily water needs to round out your nutrition targets, especially if changes in body weight, activity level, or training volume affect how much fluid you need.


How This Calculator Works

This calorie calculator uses a formula based on the Katch-McArdle equation. Unlike simpler formulas that only use weight, height, age, and gender, Katch-McArdle factors in your lean body mass - your total weight minus your body fat.

This makes it more accurate for individuals who carry more (or less) muscle than average, since muscle tissue burns significantly more calories at rest than fat tissue does.

This is why the calculator asks for your body fat percentage. That input allows it to estimate your lean mass and produce a more individualized Basal Metabolic Rate (BMR). The calculator then multiplies your BMR by an activity factor based on your reported activity level to estimate your Total Daily Energy Expenditure (TDEE).

If you do not know your current body fat percentage, use the Built With Science body fat calculator first. That estimate can help the calculator produce a more personalized starting point.

From there, it applies adjustments depending on your goal — subtracting calories for fat loss or adding them for muscle gain — at slow, moderate, and fast rates.

If building strength is part of your goal, you can also use the 1RM calculator to estimate your max and choose training weights that match your program.

Keep in mind that all calculator estimates have a margin of error of about 10-15%. Use your results as a starting point and adjust based on real-world feedback from your body. 

Calorie Calculator FAQ

A calorie deficit is when you consume fewer calories than your body burns in a day. This forces your body to tap into stored energy, primarily body fat, to make up the difference. A deficit is the fundamental requirement for fat loss; no diet works without one. 

Most people do well with a deficit of 300-500 calories below their Total Daily Energy Expenditure (TDEE). Larger deficits can speed up fat loss but also increase hunger, muscle loss, and the likelihood of burning out on your diet.
To lose weight, eat fewer calories than you burn. Select "lose weight" as your goal in the calculator above and it will estimate your daily calorie target. The calculator targets a moderate deficit that typically produces fat loss of 0.3-0.7% of your body weight per week, a sustainable pace that preserves muscle.

Track your weight weekly and adjust if progress stalls - you can either reduce calories by 100-200 per day or increase your daily step count by 1,000-2,000 steps. Both create a larger deficit, so pick whichever feels more sustainable for you.
TDEE stands for Total Daily Energy Expenditure. It's the total number of calories your body burns in a 24-hour period, including your Basal Metabolic Rate (the calories you burn at rest) plus all physical activity from workouts to walking to fidgeting.

Your TDEE is essentially your maintenance calories, eat this amount and your weight stays stable. Eat below it to lose weight; eat above it to gain weight.
BMR stands for Basal Metabolic Rate. It's the number of calories your body burns at complete rest just to keep you alive, powering your brain, heart, lungs and other organs. BMR typically accounts for 60-75% of your total daily calorie burn. 

This calculator uses a Katch-McArdle formula that estimates your BMR based on your lean body mass, which is why it asks for your body fat percentage.
BMR (Basal Metabolic Rate) is the calories you burn at complete rest - just existing. TDEE (Total Daily Energy Expenditure) is your BMR plus all the calories you burn through activity: exercise, walking, even digesting food. 

Your TDEE is always higher than your BMR. When setting calorie targets for fat loss or muscle gain, you use TDEE, not BMR - eating at your BMR would put most active people in a very large deficit.
To maintain your weight, eat at your TDEE, the number of calories your body burns in a day. The calculator above estimates this for you.  Since calculator estimates have some margin of error, treat this as a starting point. 

Eat at your calculated maintenance for 2-3 weeks while tracking your weight. If your weight stays stable, you've found your true maintenance. If it changes, adjust calories by 100-200 in the appropriate direction.
For most adults, 1,200 calories is too low. It's difficult to meet your nutritional needs at this intake, and such a large deficit often leads to muscle loss, fatigue, hormonal disruption, and eventual diet burnout. 

The only people who might appropriately eat 1,200 calories are very small, sedentary individuals whose TDEE is already low. For most people, a more moderate deficit of 300-500 calories below TDEE produces better long-term results with fewer downsides.
To lose one pound per week, you need a weekly deficit of about 3,500 calories, or 500 calories per day below your TDEE. This is a moderate deficit that works well for most people. 

However, the "3,500 calories per pound" rule is a simplification. Actual fat loss varies based on your starting body composition, how long you've been dieting, and metabolic adaptation. Use one pound per week as a rough target, not an exact expectation.
Calorie calculators provide estimates, not exact numbers. Even the most accurate formulas have a margin of error around 10-15%. This is because they can't account for individual variation in metabolism, NEAT (non-exercise activity thermogenesis), or how your body responds to different foods.

Use your calculator result as a starting point, then adjust based on what actually happens to your weight over 2-3 weeks. The calculator gets you in the ballpark; real-world tracking dials it in.
Generally, no, or at least not all of them. Fitness trackers and machines significantly overestimate calories burned during exercise, often by 30-50% or more. If you eat back all those "earned" calories, you may erase your deficit entirely. 

The activity multiplier in this calculator already factors in your overall activity level, so your exercise is somewhat accounted for. If you do extra-intense workouts beyond your normal routine, eating back 25-50% of those estimated calories is reasonable.
Once you know your calorie target, you can use the macro calculator to break it into macronutrients (protein, carbs, and fat), or set them manually. Start with protein: aim for 0.7-1 gram per pound of body weight to support muscle. Set fat at around 25-30% of total calories for hormonal health. Fill the remaining calories with carbohydrates.

To convert between calories and grams, protein and carbs are 4 calories per gram while fat is 9 calories per gram. So if your target is 2,400 calories and you weigh 180 lbs, that's roughly 180g protein (720 cal), 80g fat (720 cal), and 240g carbs (960 cal).
The Katch-McArdle equation is a formula used to estimate Basal Metabolic Rate based on lean body mass rather than just total body weight. This makes it more accurate than formulas like Harris-Benedict or Mifflin-St Jeor for people who know their body fat percentage, since it accounts for how much of your weight is muscle versus fat.

This calculator uses the Katch-McArdle formula as its foundation, then applies an activity multiplier to estimate your Total Daily Energy Expenditure.

Ready To Transform Your Body With Science?

Take our 30 second quiz below to find the most effective program for you and your fitness goals

Start Your Quiz
chevron-down-circle