I have little labels on each jar of spices that I write the “bought” date on. In general ground spices I’ll give 9 months to a year, herbs I’ll typically give about a year, and whole spices I’ll give two years. As I’m using them, I’ll check the date on the jar to see if I need to add it to my shopping list. Every once in a blue moon when I remember, I’ll also just audit my spice rack.