One conventional rule says to purchase a new mattress every ten to fifteen years. But depending on where you use it and how much punishment it takes (kids can wear out even the firmest mattress), or even the climate that you live in, you may need to replace the mattress within, say, five years. Or it may last you twenty years. Ultimately, if everything else in your life is equal-no stressors or other factors that could affect sleep-and you wake up feeling stiff and sore, you should think about replacing your mattress. Your lifestyle and your body may undergo rapid changes, so that your mattress has to change too.

As a rule, if your mattress sags, tears or looks generally shabby, you should replace it. You should also keep these questions in mind:

• Are you more tired than you were a year ago?
• Does your body ache when you wake up?
• Would a new mattress help you sleep better?