Calorie Surplus Calculator

Enter your maintenance calories (TDEE) and the daily surplus you want to run — or let the tool estimate your TDEE from the Mifflin-St Jeor equation. You'll get your target calories, the weekly weight-gain rate that surplus produces, and a protein/fat/carb macro split.

What a calorie surplus actually is

A calorie surplus means eating more energy than your body burns in a day. Your body stores that extra energy, and over time the scale goes up. Without a surplus, weight gain is essentially impossible — this is the single most important concept in bulking, building muscle, or recovering from being underweight. The question is never whether you need a surplus, but how big it should be and where the calories should come from.

How big should your surplus be?

One pound of body weight stores roughly 3,500 calories of energy. So a surplus of about 500 kcal per day adds up to ~3,500 kcal over a week — roughly one pound of gain every two weeks (0.5 lb/week). Double the surplus and you roughly double the rate. This calculator uses that conversion to translate your chosen surplus into an expected weekly rate, and it works in reverse too: pick the rate you want and read off the surplus.

For most people aiming to add muscle with minimal fat, a moderate surplus of 250-500 kcal per day is the sweet spot. Larger surpluses gain weight faster but a greater share of that weight is body fat, since the body can only build muscle at a limited rate. Research on overfeeding consistently shows that beyond a point, extra calories simply add fat. If you are significantly underweight, a larger surplus is reasonable and often necessary — just pair it with resistance training so more of the gain is lean mass.

Where the surplus calories come from

Total calories drive the scale, but macronutrient quality drives body composition. Protein protects and builds muscle; carbohydrates fuel hard training and help recovery; fats support hormones. This tool defaults protein to about 1 gram per pound of body weight (a research-supported level for muscle gain), sets fat at roughly a quarter of calories, and fills the rest with carbohydrates. If you struggle to eat enough, lean on calorie-dense foods — nut butters, olive oil, whole milk, granola, dried fruit, and rice — rather than just eating larger volumes of low-calorie food.

Sources: Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990 (PubMed) · Academy of Nutrition and Dietetics · NIH / NIDDK Weight Management · Mayo Clinic.

Frequently asked questions

How many calories is a good surplus?

For most people, 250-500 calories above maintenance per day is a good starting surplus — enough to gain steadily while keeping fat gain modest. Significantly underweight individuals may use a larger surplus under guidance.

How much weight will a 500 calorie surplus add?

Because a pound of body weight stores about 3,500 calories, a consistent 500 kcal daily surplus adds roughly one pound every two weeks, or about 0.5 lb per week, on average.

Can I calculate a surplus without knowing my TDEE?

Yes. Switch the toggle to "estimate it" and the calculator computes your BMR with the Mifflin-St Jeor equation and multiplies by an activity factor to estimate TDEE, then adds your surplus.

Will a bigger surplus build muscle faster?

Only up to a point. The body builds muscle at a capped rate, so beyond a moderate surplus the extra calories mostly become fat. A lean bulk with a 250-500 kcal surplus and progressive resistance training is the most efficient approach for most people.

Why is my real weight change different from the estimate?

Predictive equations carry about a 10% error and daily weight fluctuates with water, glycogen, and food in transit. Judge progress by the weekly average over 2-3 weeks, not day-to-day, and adjust by 100-200 kcal as needed.

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