Over eat one day, Under eat the next?

Scientifically, your body doesn't function on a day-by-day basis. It's more of a weekly and even monthly average calorie consumption.

Your body won't know the difference if you eat 1500 one day and 3000 the next. I do this all the time as a matter of fact and have lost/gained/maintained weight just fine.

If you have the willpower/self-control to stick to your calories then yes, IT'S PERFECTLY OK.