How to Use the Weight Gain Calculator
The weight gain calculator estimates how many calories you need to eat daily to reach your target weight. Fill in your details below and get a personalized week-by-week calorie and weight projection.
- Unit system: Choose metric (kg, cm) or imperial (lbs, ft/in).
- Sex: Select your biological sex — it affects your BMR formula.
- Height: Enter your height (50 cm – 299 cm, or 1'8" – 9'11").
- Current weight: Enter your current weight (15–700 kg / 33–1543 lbs).
- Age: Enter your age in years (18–120). Younger and older individuals have different metabolic rates.
- Activity level: Choose the option that best describes your typical week.
- Target weight: Your desired weight goal. Must be greater than your current weight (20–300 kg / 44–661 lbs).
- Pace: Normal (0.5 kg / 1 lb per week) or Strict (1 kg / 2 lbs per week).
Results include your maintenance calories (TDEE), the daily calorie surplus needed, and a week-by-week table showing how your weight and required calorie intake will change until you reach your goal.
Risks Associated with Being Underweight
Being underweight is not just a cosmetic concern — it carries real health risks:
- Malnutrition and vitamin deficiencies
- Osteoporosis and weakened bones
- Decreased immune function
- Reduced fertility
- Increased risk of complications during surgery or illness
- Fatigue and lack of energy
A BMI below 18.5 is generally considered underweight. If you are concerned about your weight, consult a healthcare professional.
How to Gain Weight?
To gain weight, you need to consume more calories than you burn — a calorie surplus. Here are evidence-based tips:
- Don't skip main meals. Eat breakfast, lunch, and dinner consistently.
- Add calorie-dense snacks: nuts, nut butter, oat bars, avocado, cheese.
- Boost meals with toppings: seeds, olive oil, sauces, full-fat dairy.
- Eat before drinking — beverages can reduce appetite.
- Prioritize protein to support muscle gain alongside the calories.
- Consider strength training to ensure gained weight is lean muscle.
- Track your intake using a food diary or app to confirm you're hitting your calorie targets.
How Many Calories Do I Need to Gain Weight?
Your calorie needs are determined by your Total Daily Energy Expenditure (TDEE), which depends on:
- Basal Metabolic Rate (BMR) — calories burned at rest (based on age, sex, height, weight)
- Physical activity — the more active you are, the higher your TDEE
- Thermic effect of food — energy used to digest and absorb nutrients
To gain weight, add a calorie surplus on top of your TDEE:
- Normal pace (+0.5 kg / 1 lb per week): +500 kcal/day surplus
- Strict pace (+1 kg / 2 lbs per week): +1,000 kcal/day surplus
It takes approximately 7,000–7,700 kcal to gain 1 kg of body weight, or about 3,500 kcal per pound.
Behind the Scenes of the Weight Gain Calculator
This calculator uses the Mifflin-St Jeor equation to calculate BMR — widely regarded as the most accurate formula for non-athletic adults:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
BMR is then multiplied by an activity factor to get TDEE. The calorie surplus is added to TDEE and recalculated weekly as your weight increases — making the projection dynamic and more accurate than a static estimate.
Disclaimers and Warnings
- This calculator provides an estimate only. Individual metabolism varies.
- Not suitable for children under 18, pregnant or breastfeeding individuals.
- Consult a doctor or registered dietitian before making significant dietary changes.
- Rapid weight gain (more than 1 kg/week) may lead to excess fat storage rather than lean mass.
- The projections assume a consistent calorie intake and activity level.
Frequently Asked Questions
Is it healthy to gain weight quickly?
Gaining more than 1 kg (2 lbs) per week is generally not recommended. Faster gains tend to result in more fat storage than muscle. A slow, steady approach with strength training yields better body composition.
Should I use metric or imperial units?
Both work equally well. The calculator converts internally, so choose whichever unit you're more comfortable with.
Why does my required calorie intake increase each week?
As your weight increases, your BMR and TDEE increase too. The calculator recalculates your energy needs each week based on your new projected weight, so the calorie target grows slightly over time.
What activity level should I choose?
- Little / Sedentary: Desk job, minimal movement
- Light (1–2x/week): Light walks or occasional gym sessions
- Moderate (3–5x/week): Regular exercise or active job
- Hard (6–7x/week): Daily intense training
- Physical job / Intense exercise: Manual labor + training
- Professional athlete: Twice-daily training sessions
Can I use this calculator if I'm pregnant?
No. Pregnancy weight gain has specific medical guidelines. Please use a dedicated pregnancy weight gain calculator and consult your healthcare provider.