The first area to give attention to is your sleep experience.
When you wake how do you feel? Are you regularly waking with feelings of stiffness? Do you find that any of your body members are often feeling numb? In general, discounting other health problems, do you wake with aches and pains? If you are experiencing any of these things regularly then your mattress could be the problem.
Another way to tell if a mattress need to be replaces is to make a comparison.
Compare how you sleep in your bed with how you feel after sleeping in a hotel bed or possibly in a friends guest bed.
This takes a little forethought, but if you take advantage of such opportunities it can tell you some important things about your mattress at home.
If you are married, you can prompt your mate to help you with such an analysis.
There are of course some more obvious sings that a mattress should be replaced.
If a mattress has areas where it sags, such as a permanent dip in the contour of the mattress, it should be replaced.
Even if the sag is restricted to a small area it can cause problems for the sleeper.
Lumps in the mattress are also a clear sign that it is overdue for replacing.
Furthermore, if the mattress top or sides are wearing through or the internal parts of the mattress are exposed it is definitely time to replace it.
Depending on the materials used in the construction of a mattress, it will last varying lengths of time.
As a general rule however, if a mattress has been in continuous use for 5 to 7 years it is probably nearing the end of its life.
As was mentioned before, just because a mattress feels comfortable when you lay on it, this does not mean that it is still giving you proper support.
Is it time to replace your mattress? Taking the time to periodically examine how you are sleeping and what the condition of your mattress is can help you answer that question.
Finally, investing in a good nights sleep makes sense for all aspects of a persons life.