I called Home Depot the other day asking just this question. We bought four gallons of paint 1 1/2 years ago to do my kids' bedrooms. Never got done, and now we're in the process of building another house, so I hate to waste my time on this house now. I called to see if paint would still be good for the new house since it would be about 2 1/2 years old then. She asked if it had been stored indoors (it has), and she said it should be fine for at least 3-4 years, especially since it had never been opened. She then added that she had just used some paint that her parents had used in 2001 to do a room at her house with no problems.