Is mattress sagging normal?
People worry about mattress sagging when they buy a brand new mattress.
They also wonder if their old mattress sagging is something normal and what can they do to fix it.
Mattress sagging is a normal thing.

For a brand new mattress or an old mattress. It all depends if the mattress sagging appeared from a normal wear or from your mattress being too old. It also might be the time to consider going shopping fir a brand new mattress.
Mattress sagging for a brand new mattress
When you buy a brand new mattress, sagging might appear as a normal wear in a while. But, not more than couple inches. If you feel uncomfortable sleeping on a brand new mattress, because of sagging, is time to check how deep is the sagging.
Mattress sagging & warranty
Every mattress manufacturer has it’s own rules when it comes to sagging. But, most of them, agree that if the sagging is more than 2 inches it is a manufacturer issue. And they can replace the mattress under the warranty. The mattress warranty is very important, when it comes to mattress defects.
Mattress sagging for an old mattress
Some old mattresses might have that sagging in the middle of the bed. It all depends for how long you had that mattress. If you had the mattress longer than 5 years sagging might be something normal. Depending on the mattress quality, your mattress can resist for 5- 10 years before you can feel that sink in the middle of the mattress. Other mattresses that do not have a good support and inferior quality can begin to sink in less than 3 years.
Why your mattress can sink in?
Mattress support
A mattress that has a proper support will last longer. When buying a mattress is best to buy it in a set - mattress & box spring. If you have a platform bed, that also counts as a good mattress support. In that way you know that your mattress will have the support it needs for longer.

Some customers buy a brand new mattress and use the older box spring. That old box spring can cause the sagging for your brand new mattress.
Mattress materials
The quality of the mattress materials have a huge impact on the lifespan of the mattress. If the quality of the mattress is better, the sagging will not happen soon on your mattress.