We all accept that eating away from home can add more calories.

Some days you are "good" and eat less, and some days you are "bad" and eat more, but the assumption is that it averages out to 2, 000 calories per day over the long run.

If you take in more calories than you are burning then you gain weight.

Note that the graph assumes that you, like most people, eat a random number of calories per day.

Even so, I calculated that for the next eight days, we’d have to survive on 450 calories per day.