How the Calorie Calculator Works
This calculator estimates how many calories you burn per day — your Total Daily Energy Expenditure (TDEE) — then adjusts that number based on your goal. Eat at your TDEE to maintain weight. Eat below it to lose fat. Eat above it to gain muscle.
The calculation starts with your Basal Metabolic Rate (BMR), which is the number of calories your body burns at complete rest just to keep you alive — breathing, pumping blood, maintaining body temperature. BMR is then multiplied by an activity factor to account for movement and exercise.
The Formulas
By default, this calculator uses the Mifflin-St Jeor equation, published in 1990 and widely considered the most accurate BMR formula for the general population:
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
If you enter your body fat percentage, the calculator switches to the Katch-McArdle formula, which uses lean body mass instead of total weight. This is more accurate for people who are particularly lean or carry more muscle than average:
Lean mass = weight × (1 − body fat % ÷ 100)
Activity Multipliers
Your BMR is multiplied by a factor based on how active you are throughout the week. These multipliers account for both structured exercise and general daily movement (walking, standing, fidgeting).
| Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, no training |
| Light | 1.375 | 1-2 training days per week |
| Moderate | 1.55 | 3-4 training days per week |
| Heavy | 1.725 | 5-6 training days per week |
| Athlete | 1.9 | Twice daily or hard labor + training |
Most people overestimate their activity level. If you spend most of your non-gym time sitting, choose Sedentary or Light regardless of how hard you train.
Macros: Protein, Fat, and Carbs
Protein is set at 1g per pound of bodyweight (2.2g/kg). This might seem high — especially during a cut, where you're eating less food overall — but that's exactly when protein matters most. When you're in a calorie deficit, your body is looking for energy wherever it can find it, including your muscle tissue. Higher protein intake signals your body to preserve muscle and burn fat instead. Research consistently shows that protein intakes of 0.9-1.1g/lb during a deficit significantly reduce muscle loss compared to lower intakes. During a bulk, 0.7-0.9g/lb is sufficient since the calorie surplus itself is muscle-sparing, but rounding up to 1g/lb keeps things simple across all goals.
Protein also has the highest thermic effect of any macronutrient — your body burns roughly 20-30% of protein calories just digesting it, compared to 5-10% for carbs and 0-3% for fat. And it's the most satiating macro, meaning it keeps you fuller longer. Both of these effects are especially valuable when calories are restricted.
Fat is set at 25% of total calories. This supports hormone production, joint health, and absorption of fat-soluble vitamins (A, D, E, K). Going below 20% long-term can impair recovery and hormonal function.
Carbohydrates fill the remaining calories. Carbs are the primary fuel for high-intensity training. Cutting them too aggressively will hurt performance before it improves body composition.
How Fast Should I Lose Weight?
A deficit of 500 calories per day produces roughly 1 pound of fat loss per week (3,500 cal ≈ 1 lb). This is the most commonly recommended pace — fast enough to see results, slow enough to preserve muscle and avoid metabolic adaptation.
Larger deficits (750-1,000 cal/day) can work for people with more fat to lose, but increase the risk of muscle loss, fatigue, and diet adherence problems. This calculator warns you if your deficit exceeds 35% of your TDEE.
How Fast Should I Gain Weight?
A surplus of 250-300 calories per day is sufficient for most people to build muscle without excessive fat gain. Larger surpluses don't accelerate muscle growth — they just add more fat. Natural lifters can gain roughly 0.5-1 lb of muscle per month under optimal conditions, so a controlled surplus is ideal.
How Accurate Is This?
All calorie calculators are estimates. Individual metabolism varies based on genetics, body composition, hormonal status, sleep quality, stress, and non-exercise activity thermogenesis (NEAT). Use the number as a starting point, weigh yourself daily for 2-3 weeks, look at the trend, and adjust. If your weight isn't moving in the direction you want, change your intake by 200-300 calories and reassess.
Frequently Asked Questions
How many calories should I eat per day?
It depends on your age, sex, height, weight, and activity level. Most adults need between 1,600 and 3,000 calories per day to maintain weight. Use the calculator above for a personalized estimate, then subtract 500 calories to lose about 1 pound per week or add 250-300 to gain weight gradually.
What is the most accurate calorie calculator formula?
The Mifflin-St Jeor equation is considered the most accurate for the general population. If you know your body fat percentage, the Katch-McArdle formula can be more precise because it accounts for lean body mass rather than total weight.
How many calories should I eat to lose weight?
A safe and sustainable rate is 1-2 pounds per week, requiring a daily deficit of 500-1,000 calories below your TDEE. Deficits larger than 35% of your TDEE are not recommended — they increase muscle loss, tanked energy, and the likelihood of regaining the weight.
What is TDEE?
Total Daily Energy Expenditure is the total number of calories your body burns in a day from all sources: basal metabolism, physical activity, and digesting food. It represents your maintenance calories — eating this amount keeps your weight stable.
Should I eat the same calories on rest days?
For most people, keeping calories consistent every day is the simplest and most effective approach. If you prefer, you can eat slightly less on rest days and more on training days, as long as your weekly average hits your target.