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Weight Gain Calculator

Gaining weight in a healthy, controlled way requires eating above your Total Daily Energy Expenditure (TDEE) — a calorie surplus. This calculator estimates your TDEE, adds your chosen surplus, and breaks down the optimal protein, carbs, and fat targets to maximise muscle gain while minimising excess fat accumulation. Set an optional goal weight to see how long your bulk will take.

Quick Answer

To gain 0.5 lb per week, eat about 250 calories above your TDEE daily. Pair this with resistance training and adequate protein to maximise muscle gain.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter your details above to calculate your calorie surplus.

How the Formula Works

  1. Calculate your TDEE using the Mifflin-St Jeor equation and an activity multiplier.

    TDEE = BMR × Activity Multiplier

  2. Add your chosen calorie surplus to your TDEE to get your daily calorie target.

    Daily Calories = TDEE + Surplus

  3. Estimate weekly weight gain using the 3,500-calorie rule.

    Weekly Gain (lbs) = (Surplus × 7) / 3,500

  4. Distribute macros for gaining: 1 g protein per lb of bodyweight, 25% of calories from fat, and the rest from carbohydrates.

    Protein = 1 g × bodyweight (lbs) | Fat = 25% of daily calories | Carbs = remainder

Methodology & Sources

Reviewed and updated April 5, 2026 · Prepared by GetHealthyCalculators Editorial Team

References

  • Evidence-based recommendations for natural bodybuilding contest preparation · Journal of the International Society of Sports Nutrition
  • Dietary protein for athletes: From requirements to optimum adaptation · Journal of Sports Sciences
  • A new predictive equation for resting energy expenditure in healthy individuals · American Journal of Clinical Nutrition

Limitations

  • The 3,500-calorie-per-pound rule is a simplification — actual weight gain rate varies with genetics, training volume, and adherence.
  • TDEE estimates have a margin of error of roughly 10%; your actual maintenance calories may differ.
  • The protein recommendation of 1 g per lb of bodyweight is conservative and appropriate for most people; some research supports up to 0.8–1.2 g per lb for maximising muscle protein synthesis.
  • This calculator assumes all weight gained is a mix of muscle and fat; actual body composition change depends heavily on training quality and consistency.
  • Results are projections only. Individual metabolic adaptation, sleep quality, and stress levels all influence outcomes.

Frequently Asked Questions

How many calories do I need to gain weight?
You need to eat more calories than your body burns each day. Add 250–600 calories above your TDEE depending on how quickly you want to gain. A surplus of 250 cal/day adds roughly 0.5 lb per week, while 600 cal/day can add up to 1.2 lbs per week.
How much protein do I need when bulking?
Aim for approximately 1 gram of protein per pound of bodyweight per day. This supports muscle protein synthesis during a calorie surplus and minimises the proportion of fat gained. Higher intakes (up to 1.2 g/lb) are unlikely to cause harm and may offer marginal additional benefit.
What is a lean bulk?
A lean bulk uses a small calorie surplus (around 250 cal/day) to add muscle gradually while keeping fat gain to a minimum. Progress is slower than an aggressive bulk, but body composition improvements are often more noticeable because less fat accumulates alongside the muscle.
Is it possible to gain muscle without gaining fat?
Body recomposition — gaining muscle while simultaneously losing fat — is possible, particularly for beginners and those returning to training after a break. However, for most intermediate and advanced lifters, a modest surplus with high protein and consistent resistance training is the most practical strategy for muscle gain.
How long should a bulk last?
Most structured bulks last 8–20 weeks, depending on starting body composition and goals. Bulking when your body fat is already elevated (above ~15–20% for men or ~25–30% for women) can increase fat gain disproportionately. Many lifters alternate bulk and cut phases across the year.
Why is there a warning for very high calorie targets?
Eating above 5,000 calories per day is unusual for most non-elite athletes and may be a sign of an over-estimated TDEE or an unrealistically large surplus. Very high intakes can be difficult to sustain, may cause digestive discomfort, and tend to accelerate fat gain. A registered dietitian can help personalise very high calorie plans.

Fine-tune your bulk with the Lean Bulk Calculator

Lean Bulk Calculator

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