Health

Weight Gain Calculator

Calculate the daily caloric surplus you need to reach your target weight within your chosen timeframe. Optionally enter your TDEE to get a precise daily calorie target.

Enter your weights and timeframe to see the result.

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Caloric Surplus Formula

Weight gain is driven by a sustained caloric surplus above your maintenance level. The required daily surplus is derived from your target weight gain and the energy density of body tissue.

Daily Surplus = (Gain × 3,500 kcal/lb) ÷ Days

Daily Target = TDEE + Daily Surplus

Example: 10 lb gain over 70 days = 500 kcal/day surplus

Planning a Smart Bulk

Gaining weight without a plan often leads to excess fat accumulation rather than lean mass. A structured approach — sometimes called a lean bulk — uses a controlled caloric surplus of 200 to 500 calories per day above maintenance. This pacing gives your muscles time to actually absorb and use the extra energy for growth.

Protein intake is the most important dietary variable. Eating sufficient protein, typically 0.7 to 1 gram per pound of body weight per day, ensures your body has the building blocks for muscle synthesis. Total calorie intake drives the rate of weight gain; protein quality and distribution drive how much of that gain is muscle versus fat.

Track your actual weight weekly by weighing yourself under consistent conditions, such as first thing in the morning. If you are gaining faster than your target rate, reduce the surplus slightly. If progress has stalled, consider increasing calories by 100 to 200 per day and reassessing in two weeks.

Frequently asked questions

How do I calculate the calories needed to gain weight?
To gain weight, you need to consume more calories than your body burns. One pound of body weight roughly equals 3,500 calories, while one kilogram equals approximately 7,700 calories. To find your daily surplus, multiply your total weight gain goal by this factor and divide by the number of days in your plan. Add the result to your TDEE to get your daily calorie target.
How fast can I gain weight healthily?
A healthy rate of weight gain for most people aiming to build muscle is 0.25 to 0.5 pounds per week, or roughly 0.1 to 0.25 kilograms per week. Faster gains are largely fat rather than muscle. For people who are underweight and primarily need to restore body mass, rates up to one pound per week may be appropriate. Always consult a healthcare professional if you have medical reasons for weight gain.
What is TDEE and why does it matter for weight gain?
TDEE stands for total daily energy expenditure — the total number of calories your body burns in a day including your basal metabolic rate, the thermic effect of food, and your activity level. To gain weight, you must eat above your TDEE. Knowing your TDEE makes it possible to set a precise daily calorie target rather than guessing. Use a TDEE calculator to find this number based on your height, weight, age, and activity.
Should I eat a large surplus or a small surplus to gain muscle?
Research on natural (non-assisted) athletes suggests that a lean bulk with a modest surplus of 200 to 300 calories per day above TDEE maximises the ratio of muscle gained to fat gained. Larger surpluses do lead to faster total weight gain but the additional mass is predominantly fat. Beginners can often gain muscle effectively with a 200 to 400 calorie surplus, while experienced athletes may need less.
What should I eat to gain weight in a healthy way?
To gain weight healthily, prioritise a high protein intake of 0.7 to 1 gram per pound of body weight to support muscle synthesis. Carbohydrates are the primary fuel for training and recovery. Healthy fats from sources like nuts, avocado, and olive oil support hormonal health. Eat calorie-dense foods such as whole grains, legumes, dairy, eggs, and lean meats to hit your calorie surplus without relying on junk food.
Does strength training matter when trying to gain weight?
Yes, resistance training is essential if your goal is to gain lean muscle mass rather than primarily fat. Without a training stimulus, a caloric surplus will be stored predominantly as fat. Progressive overload — gradually increasing the weight or volume in your workouts — signals the body to build muscle tissue using the extra calories. Aim for three to four strength sessions per week focusing on compound movements like squats, deadlifts, and presses.

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