Calories don’t matter….but they kind of do

So, if you personally eat two meals a day of vegetables protein and a fat, and no snacks – that is probably around 1200 calories, yes?
Just wondering – do you find that you gain weight if you eat a little bit more on some days? or if you get really hungry and have a late dinner, do you let yourself eat a snack before dinner?
And/or – how do you account for unexpected changes? (Sometimes my day doesn’t go how I planned it the night before. And I don’t want to feel uptight or stressed out if my husband/kids throw a curveball…).