To gain one pound of body weight, you generally need to consume an extra 3,500 calories beyond what your body burns. This is a widely accepted rule often referred to as the "3,500 calorie rule"

. However, some research suggests that the exact number can vary slightly, with estimates ranging from about 3,436 to 3,752 calories per pound of body fat, depending on individual factors and body composition

. For practical purposes:

• Eating an additional 500 calories per day over your maintenance level would theoretically lead to about one pound of weight gain per week (500 calories/day × 7 days = 3,500 calories)

• To gain weight more quickly, a surplus of 1,000 calories per day might result in about 2 pounds gained per week, though individual results vary based on metabolism, activity level, and body composition

It's important to note that weight gain includes not only fat but also muscle and water, depending on diet and activity. Also, the 3,500 calorie rule is a useful guideline but not a precise predictor for everyone, as metabolic adaptations and other factors influence actual weight changes

. In summary:

• About 3,500 extra calories are needed to gain one pound of body weight.
• A daily surplus of 250 to 500 calories is recommended for safe, gradual weight gain.
• Individual variations exist, so monitoring progress and adjusting intake is key.

This approach helps ensure weight gain is more controlled and can prioritize muscle over fat if combined with appropriate exercise