Many of the brewing softwares (
ProMash, for example) will calculate the loss of your hops bittering potential based on storage time and conditions.
A couple examples of resulting apha acid levels, starting with 10% alpha whole hops:
Stored 3 months, barrier pack/airtight, at 0F (freezer): 9.7%
Stored 3 months, barrier pack/airtight, at 40F (fridge): 9.2%
Stored 3 months, barrier pack/airtight, at 65F (room): 8.5%
Stored 3 months, plastic bag, at 65F (room): 8.1%
Stored 6 months, barrier pack/airtight, at 0F (freezer): 9.4%
Stored 6 months, barrier pack/airtight, at 40F (fridge): 8.5%
Stored 6 months, barrier pack/airtight, at 65F (room): 7.3%
Stored 6 months, plastic bag, at 65F (room): 6.6%
Stored 12 months, barrier pack/airtight, at 0F (freezer): 8.8%
Stored 12 months, barrier pack/airtight, at 40F (fridge): 7.2%
Stored 12 months, barrier pack/airtight, at 65F (room): 5.3%
Stored 12 months, plastic bag, at 65F (room): 4.3%
Basically, you can estimate losing ~1% of your alpha per month under ideal storage conditions, roughly 2x that in the fridge, and 4x at room temp.