The time it takes to gain weight depends on various factors including calorie intake, metabolism, age, sex, activity level, and health status. Generally, if you consume about 500 extra calories per day above your maintenance needs, you can expect to gain approximately 15 pounds (6.8 kg) over six months. This slower approach tends to promote muscle gain rather than fat

. If you increase your calorie intake by about 1,000 calories daily, you might gain around 25 pounds (11.4 kg) in six months, but a larger portion of this gain is likely to be fat

. Weight gain is not linear; as your body adjusts, you may need to increase calories further to continue gaining weight. Most people follow a weight gain protocol for at least six months before transitioning to maintenance to allow their body to stabilize at the new weight

. The rate of weight gain can be faster if eating significantly above maintenance, with some people gaining about 2 pounds per week when consuming over 1,000 extra calories daily, though this may lead to more fat gain

. In summary:

• Moderate surplus (~500 calories/day): ~15 pounds in 6 months, mostly muscle if combined with resistance training.
• Larger surplus (~1,000 calories/day): ~25 pounds in 6 months, more fat gain likely.
• Faster gains possible but often result in higher fat accumulation.
• Weight gain varies by individual factors like genetics, metabolism, and activity level

A gradual, consistent increase in calories combined with strength training is the recommended approach for healthy weight gain.