Weight Gain Calculator
Calculate the caloric surplus needed for healthy weight gain. A surplus of 300-500 calories/day promotes lean muscle gain of ~0.5 lb/week when combined with resistance training. Higher surpluses risk excess fat gain.
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Evidence-based formulas Mifflin-St Jeor BMR ISSN protein guidelines
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📊 Weight Progress
📊 Caloric Breakdown
📊 Weight Projection
📊 Macro Split
Weight Gain Plan
Surplus: 458 cal/day. Gain 10.0 kg in 24 weeks. Protein: 117g/day.
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
— ACSM
— ISSN
Healthy weight gain requires a caloric surplus of 300-500 calories/day for lean muscle (~0.25-0.5 lb/week). Resistance training is essential—diet alone adds fat. Protein at 1.6-2.2g/kg maximizes muscle protein synthesis. Higher surpluses (>500 cal) risk excess fat gain. BMR uses Mifflin-St Jeor; TDEE = BMR × activity factor.
Sources: WHO, NIH, ACSM, ISSN.
Key Takeaways
- • 300-500 cal surplus promotes lean gain; higher = more fat
- • Protein 1.6-2.2g/kg with resistance training 3-5x/week
- • Beginners gain muscle faster; advanced lifters 0.5-1 lb/month
- • Underweight (BMI <18.5) benefits from gradual gain to healthy range
Did You Know?
How Does Weight Gain Work?
Caloric Surplus
Calories in > Calories out. BMR (Mifflin-St Jeor) × activity factor = TDEE. Add 300-500 cal for lean gain.
Protein for Muscle
1.6-2.2g/kg supports muscle protein synthesis. Without resistance training, surplus becomes fat.
Rate of Gain
0.25-0.5 lb/week = lean. 1+ lb/week = more fat. Timeframe determines weekly rate: gain / weeks.
Expert Tips
Surplus vs. Gain Rate
| Daily Surplus | Weekly Gain | Assessment |
|---|---|---|
| 250 cal | ~0.25 lb | Very lean, slow |
| 300-500 cal | 0.25-0.5 lb | Optimal lean gain |
| 500-750 cal | 0.5-0.75 lb | Moderate fat gain |
| >750 cal | >1 lb | Excess fat gain |
Frequently Asked Questions
How many calories do I need to gain weight?
Add 300-500 calories above your TDEE for lean muscle gain (~0.25-0.5 lb/week). A 500 cal/day surplus yields ~1 lb/week. Higher surpluses increase fat gain. Use the Mifflin-St Jeor equation for BMR, then multiply by activity factor for TDEE.
What is a healthy rate of weight gain?
For lean muscle: 0.25-0.5 lb per week (100-250g). Beginners may gain 1-2 lbs/month of muscle; advanced lifters 0.5-1 lb/month. Gaining faster than 1 lb/week typically adds excess fat.
How much protein for muscle gain?
Target 1.6-2.2g per kg bodyweight (0.7-1g per lb). Research shows 1.6g/kg maximizes muscle protein synthesis. Spread intake across 4-6 meals. Resistance training is essential—diet alone won't build muscle.
What causes slow weight gain?
High metabolism, poor appetite, inadequate calories, or digestive issues. Solutions: liquid calories (shakes, milk), smaller frequent meals, calorie-dense foods (nuts, avocado), and tracking intake. Medical conditions may require a doctor's evaluation.
Is weight gain safe for underweight people?
Yes. BMI <18.5 indicates underweight; gaining to a healthy range improves bone density, immune function, and energy. Aim for 0.5-1 lb/week with nutrient-dense foods. Consult a provider if you have eating disorders or medical conditions.
Can this calculator replace medical advice?
No. This tool is for educational purposes only. Consult a healthcare provider before starting any weight gain program, especially if underweight, recovering from illness, or taking medications.
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any weight gain program, especially if underweight, recovering from illness, or taking medications.
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