To start with, there's no set formula for when you should purchase a new mattress. It often depends on the individual mattress itself. Some become worn, less comfortable and less supportive within a couple of years whereas other higher quality mattresses can last over a decade.
However, there are some important signs which indicate when you should consider purchasing a new mattress. These include:
If you wake up aching or tired this is a sign that you've been sleeping in discomfort, leading to poor quality sleep
If you tend to sleep better in other beds or look forward to sleeping in other beds, perhaps when away on holiday
If your mattress is starting to feel bumpy it's time for a new one
Have you looked after your mattress? Flipping a mattress regularly can help to extend its life
Sealy Queen Mattress
In addition to the above points people over the age of 40 should consider renewing their mattress every 5-7 years as their tolerance to uneven and unsupportive mattresses is much lower compared to younger people.
There is also the make of mattress to consider. Some of the higher quality mattress brands, such as Hypnos and Sealy, are manufactured at the highest quality. You can expect mattresses produced by these companies, provided they aren't at the cheap end, to last longer than some of the more inexpensive mattress brands, such as Snuggle and Myer's Beds.
However, in general we would recommend buying a new mattress within every 7 years. It's far better to be safe than sorry and a poor quality mattress can lead to years of less than perfect health. In fact, in the UK the most common cause of sleeping complaints at doctor's surgeries is an old, poor quality mattress. Therefore if you've had your existing mattress for a while often the best investment you can make is in a new one.