Gaining weight is like losing weight. If you want it to stay you need a lifestyle change. Slowly but surely increasing calories so that you have a decent excess every or most days will work better long term. Instead of going crazy stuffing yourself could get exhausting quick and expensive too. Granted some people can do it that way. One of the biggest mistakes I see new gainers make (not that I'm an expert or anything
) is not realizing how many calories they need to gain and then how many pounds/kilograms they need to gain for it to be noticeable. Starting off with a food diary to keep track of how many calories you're eating in a day is a great way to know if you need to make adjustments. It also allows you to add up the excess calories and get an idea how long it will take to gain each pound. We need about 2000-2500 calories a day just to exist. That isn't counting any calories burned from any physical activity. Then it takes 3500 calories in excess of your daily calories to gain 1lb of body fat. Further still it takes usually more than 5-10lbs of fat to even start to notice a change depending on how your body stores it. I don't say this to scare you away. Just to have realistic expectations. Gaining is a slow and steady process that takes time. I've found that I make sure to eat 2500 calories a day then I use heavy cream or other high calorie things to add the excess each day. Heavy cream isn't for everyone. But 1 quart has 3500 calories. So basically you'll gain 1lb everytime you finish one. As long as you are eating your daily calories. It doesn't have to be heavy cream, many things can do the job. High fat and high calorie things can also take one's digestive track some time to get used to. Usually best to have smaller amounts thru the day or after eating to aid in digestion. Hopefully some of that info helps. There are many weight gain calculators online. Finding out how many calories you'll need to eat a day to say gain 10lbs in a month makes it much easier to plan and make sure you are eating enough each day. Best of luck!