The press test
Place your pillow on a firm surface, such as a table, and press down the middle.
Does it loft back into shape when you remove your hand? Then it's still good to use.
If the pillow stays flat after you remove your hand, it's time to replace it.
The simple tests have been shared by the experts at the Tielle Love Luxury's pillow swap programme in the UK, according to the Daily Mail.
They've also explained that the type of pillow you should purchase depends on what position you normally prefer to sleep in.
People who like to sleep on their back should choose a soft pillow that won't put a lot of stress on the neck.
Those who prefer to sleep on their side need a higher and firmer pillow, to keep their neck aligned with their spine.
If you toss and turn a lot, you should go with a medium height pillow.