When you pick your own pumpkin, cure it so it will last longer, say horticulturists with the University of Georgia Extension Service. Most commercially sold pumpkins are already cured.
Curing takes 10-20 days. It's best done in a room 80-85 degrees. Since you probably won't have that in your home, just keep it in a dry place, like an air-conditioned room. Leave it undisturbed and don't handle it.
Once cured, the pumpkin can last two to three months if stored at 50-55 degrees.
Don't put a pumpkin in the refrigerator, though. If you get them too cool, they'll get pits in the surface that can cause rot.
Whether you buy your pumpkin pre-picked or pick it yourself, make sure you store it where there is good air movement all around.