Remember folks who are currently subscribed: They do not give prorated refunds for full year subs. When you cancel the service ends immediately. Setup calendar reminders or eat the sunk cost now because Amazon Prime is just a typical subscription entrapment scheme that will only get harder and harder to cancel, like a gym membership.
Edit: Thanks /u/@firadin - Cancel now, you don't lose anything and the membership simply won't renew on your renewal date.
Is that new? When I cancelled last year a couple months into my year long subscription I got the money back for the unused months. No problem, easy too.
That's not accurate, they don't stop your benefits when you hit the cancel button. I just cancelled today and have my benefits until the end of my yearly subscription in November.