Weight Gain Calculator — Calories & Time to Gain Weight
Find out exactly how many calories you need to eat each day to reach your target weight — plus your TDEE, weekly gain rate, protein needs, and a projected timeline to your goal.
kg
kg
cm
years
Biological sex
Activity level
kcal/day
TDEE + surplus — eat this daily to gain weight at the chosen rate
- 1
BMR (Mifflin–St Jeor)
10 × 70 + 6.25 × 175 − 5 × 25 + 5 = 1,674 kcalBasal Metabolic Rate — calories the body burns at complete rest. - 2
TDEE = BMR × activity factor
1,674 × 1.55 = 2,594 kcal - 3
Daily target = TDEE + surplus
2,594 + 500 = 3,094
How does this calculator work?
Your daily calorie target for weight gain = TDEE + surplus. TDEE is calculated from the Mifflin–St Jeor BMR multiplied by an activity factor. A 500 kcal/day surplus adds roughly 0.45 kg/week. Time to goal ≈ (kg to gain × 7 700) ÷ daily surplus ÷ 7 weeks. Protein recommendation is 1.8 g/kg of target body weight.
Formula
How this is calculated
The calculator first estimates your Basal Metabolic Rate (BMR) using the Mifflin–St Jeor equation — the most accurate single-equation predictor of resting energy expenditure for most adults: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 for men, and the same formula − 161 for women. Your Total Daily Energy Expenditure (TDEE) is then BMR multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active). Eating above TDEE creates the surplus needed for weight gain.
A rule of thumb used by sports dietitians is that 7,700 kcal of surplus produces roughly 1 kg of body-mass gain — a blend of lean tissue and fat. At a 500 kcal/day surplus you gain about 0.45 kg per week; at 250 kcal/day you gain about 0.23 kg per week. Smaller surpluses tend to produce more muscle-to-fat gain if combined with resistance training, while larger surpluses are faster but add more fat. The timeline shown assumes the surplus remains constant — in practice, TDEE rises as body weight increases, so calorie targets should be recalculated every few weeks.
The protein recommendation of 1.8 g per kg of target body weight reflects the upper end of the evidence-based range for muscle-protein synthesis during a gaining phase. Actual protein needs may differ based on training status and individual response. This tool is intended as a practical starting point — consult a registered dietitian for personalised guidance.
Frequently asked questions
A common estimate is 7,700 kcal of cumulative surplus to gain 1 kg of body mass. At a 500 kcal/day surplus, that takes about 15–16 days. Because new tissue is a mix of lean mass and fat, the actual figure varies between individuals.
Not necessarily. Research suggests that muscle-protein synthesis saturates well below very large surpluses, so excess calories beyond roughly 300–500 kcal/day tend to be stored mostly as fat. A moderate surplus combined with progressive resistance training is the most effective approach for lean mass gain.
Yes. Your TDEE increases as your body mass grows, because larger bodies burn more energy at rest and during activity. Recalculate your target every 2–4 weeks or whenever your weight gain stalls to keep the surplus on track.
Also known as
TG we-Calculate Editorial Team. (2026). Weight Gain Calculator — Calories & Time to Gain Weight [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/weight-gain-calculator
TG we-Calculate Editorial Team. "Weight Gain Calculator — Calories & Time to Gain Weight." TG we-Calculate. 2026. https://we-calculate.com/calculator/weight-gain-calculator.
TG we-Calculate Editorial Team, "Weight Gain Calculator — Calories & Time to Gain Weight," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/weight-gain-calculator
@misc{wecalculate_weight_gain_calculator, title = {Weight Gain Calculator — Calories & Time to Gain Weight}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/weight-gain-calculator}}, year = {2026}, note = {TG we-Calculate} }
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