The "100/100" health and fitness rule of thumb is to eat 100 fewer calories a day while burning 100 more calories a day.
This from CalorieLab:
"...eliminate 100 to 200 calories a day from your diet. This “mindless margin” is too small for the body to notice, and cutting 100 calories a day will allow you to lose 10 pounds a year without doing anything else different. Cutting out a 270 calorie candy bar a day would allow you to lose 27 pounds in a year without making any other changes."
What does 200 calories look like? Click Here.