Most convertible car seats are designed to last between six and 10 years. Of course, every seat has a different expiration date, so it is worth checking beforehand or contacting the manufacturer for some more details information. You may be wondering why car seats expire in the first place. There are a number of different factors at work here. Firstly, there is the natural deterioration of materials due to heat, humidity, and age. Secondly, rust can form on the metal sections, which will impact how the seat performs in the event of a crash. There is also the general wear and tear which occurs through regular washing, tightening of straps, and switching from front-facing to rear-facing positions. It is very easy for parts and pieces to get lost over the years, and as certain models are discontinued, you may no longer be able to get replacements from the manufacturers.