It depends on several factors. The most important thing is the way they are stored. Ideally, spices and spice blends should be kept away from light and moisture. In other words, avoid leaving them on and, above all, spare them the sources of heat.
Generally, if stored in goods conditions, our spices and spice blends can be serviceable far one year. However, if they contain ingredients having nothing to do with spices (example : sugar), their shelf life may be somewhat shortened. But in this case, there is a solution that has proved its worth : put them in the fridge, this way they will be kept away from a cursory deterioration.
You have to keep in mind that spices and spice blends are living entities and as such, you have to provide them the best conditions possible if you do not wish to lose them prematurely.