How long can you keep dry?

Now that my cats are getting 80% of their diet from wet food, a bag of dry lasts me a long time. How long can you store dry food before it becomes rancid?

naturally preserved foods technically 6 months after opening IF ideal conditions thru the shipping and handling process ... and then kept in a cool dry place in the home

I notice that most naturally preserved foods start to smell "stale" after 2-3 months, and the cats don't like it as much. So, I try not to buy more than they will eat in a couple of months (which is not easy now that I have them on mostly wet food). Some people keep part of the bag of dry in the freezer until they need it, which apparently keeps it fresh, so I'm thinking of trying that.

I only feed dry for snacking so a small bag will last 3 months. I store dry food in a air tight container from Rubbermaid.