1. Look for signs of wear and tear
If your mattress has visible damage, it can be a rough indicator of it's present condition. A mattress can last between 5 to 10 years. But this depends on the frequency of use and the quality of the mattress. You can also look for sagging in the mattress. A sagging mattress cannot fully support your body while asleep.
2. Waking up constantly with aches and pains
How do you feel when you lay down on bed? Is it comfortable to sleep on your mattress? Sometimes the lack of support from your mattress is only evident from the constant backaches or neck pains you experience upon waking up in the morning. Lack of comfort gives you one more reason to trade in your old mattress with a new one.
3. Compare it with another mattress
If you get a chance to sleep on a different mattress, and feel much better, then it could be that your own mattress isn't serving it's purpose. The deterioration of your mattress takes time, making it difficult for you to figure out the change in quality. Comparing it with a new one makes it easier to assess the quality of your mattress.
4. Changes in your lifestyle
Even when your mattress is doing it's job well, your needs might change with time. Kids grow older, your partner or spouse shares your bed, or your spine demands more support from your mattress. All these can make your mattress less useful and needs replacing.