How many calories are you consuming each day in each meal?
To answer this you need to know the calorific value of each ingredient in your meal. Lets start with breakfast. The most common breakfast foods are: Low fat yogurt, chocolate donut, cereal with milk - all these range between 150 to 250 calories. Bagel and cream cheese, biscuits with sausage and egg and cheese are in the range of 450 -550 calories.
If your lunch constitutes tuna salad sandwich with whole wheat bread, grilled chicken or salmon wrap then the calories would be around 200 -300. If you consume Pizza or burger instead then it shoots up to 500 plus calories. Similarly for dinner.
Snacks if comprising a fruit or nuts would add not more than 50 to 100 calories. But team it up with chips or chocolate bar and it shoots to 300 calories.
So, choosing what you eat for each meal adds up.