How it's calculated
Your Total Daily Energy Expenditure (TDEE) is calculated using the Mifflin-St Jeor equation and your activity level, then adjusted by ±500 kcal/day for a weight-loss or weight-gain goal. Protein is set at 2 g per kg of body weight, fat at 25% of target calories, and the remainder comes from carbohydrates.
How the calorie adjustment works
| Goal | Adjustment from TDEE | Approximate rate of change |
|---|---|---|
| Lose weight | −500 kcal/day | ~0.5 kg (1 lb) per week |
| Maintain weight | No change | Weight stable |
| Gain weight | +500 kcal/day | ~0.5 kg (1 lb) per week |
Clinical use
- Protein at 2 g/kg body weight is a commonly recommended target to help preserve (or build) lean muscle mass during a calorie deficit or surplus, above the minimum needed to avoid deficiency.
- These macro splits are a reasonable general starting point, not a rigid prescription — personal preference, training goals, and specific dietary approaches (low-carb, higher-fat, etc.) can all justify different splits while still hitting the same total calorie target.
- A ±500 kcal/day adjustment is a moderate, sustainable pace of change for most people — more aggressive deficits/surpluses can work short-term but are harder to sustain and carry more risk of muscle loss (in a deficit) or excess fat gain (in a surplus).
- These are estimates based on population equations — individual metabolism varies, so treat the numbers as a starting point to adjust based on your actual measured progress over several weeks.
Frequently asked questions
How is my calorie target calculated?
Your Total Daily Energy Expenditure (TDEE) is estimated from your weight, height, age, sex, and activity level using the Mifflin-St Jeor equation, then adjusted by 500 kcal/day up or down depending on whether your goal is to gain, lose, or maintain weight.
Why is protein based on body weight instead of a percentage?
Protein needs scale more directly with body weight (and especially lean body mass) than with total calorie intake, so setting it in grams per kg — rather than as a percentage of calories — gives a more physiologically sensible target, particularly for preserving muscle during a calorie deficit.
Can I adjust the fat and carb split?
Yes — the 25% fat target used here is a reasonable default, but if you prefer a higher-fat, lower-carb approach (or vice versa), you can shift calories between fat and carbohydrate while keeping protein and total calories the same.
Why does this calculator suggest a 500 kcal/day change for weight goals?
A 500 kcal/day deficit or surplus corresponds to roughly 0.5 kg (1 lb) of weight change per week, which is a widely used, moderate and sustainable pace — more aggressive changes are possible but come with greater risk of muscle loss (when cutting) or excess fat gain (when bulking).
References
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51:241-247.
- Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. Br J Sports Med. 2018;52:376-384.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.