Basically, this is how I figure out my maintenance calories, for the next 7 days, eat like you normally would and write down everything you eat. You can use a simple free app called
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Then at the end of the week you can total up everything you ate and divide it by 7, that's the average you ate per day and that will be your approximate maintenance calories got your current body weight.
What I like to do for diet (in a perfect world), especially if your trying to get bigger, eat 1gm of protein per lb of bodyweight, get about 80gm fat from good healthy fat sources and the rest of your calories from carbs.
So say you found out your maintenance is 2000 calories per day and you weigh 165lbs, start eating about 2400 calories, maybe 2 weeks later you see that you gained 5lbs great. Once a week goes by where the scale stopped moving, add another 400 calories and repeat the process.
Just don't go from 2000-3500 or something crazy like that all at once, baby steps. A few years back I made a drastic jump from 3000 straight to 4000+ and I got super fat. Just cus your on gear don't mean you can eat junk. I learned that the hard way