Well, 1 pound of fat is 3,500 calories (above the 1,500-2,500 you probably burn a day) so eating an additional 3,500 calories (above your normal diet) per day for 30 days would only get you 30 pounds. You'd likely have to eat more than triple your normal food intake for a month (unless you're already gaining weight at a rapid clip). If you're eating 2,000 calories/day and you up that to 6,000 calories/day you'd only get to 120,000 excess calories after a month (8 pounds less than your 40 pound goal).

1 pound is more than you'd think in calories - which is one of the reasons losing weight is so hard. If you're eating 2,000 calories and cut your daily food in half, it would take over 3 days to lose a pound of fat.