So, to maintain his current body weight he will consume 2,670 calories per day. The Daily Calorie Surplus. Now you need to add 300 – 500 calories per day on top of that to build muscle. If you’re a very skinny ‘hard gainer’ then you must make sure your daily calorie surplus is closer to 400 – 500 every day. This is an ideal surplus of calories, big enough to build muscle yet small enough to avoid excessive gains in unnecessary fat. Our example male above will take his daily calorie maintenance level of 2,670 calories and consume an additional 400 calories. So, he will now eat 3,070 calories per day to build muscle mass. Of course, there’s no perfect set-in-stone calorie surplus, some people might do great with 300, while others do better with 500. You might find that you’re gaining too much fat with 500, and you need to cut back a bit.