Annual iCloud storage plans [Archived document = policy no longer active] - https://support.apple.com/HT201058
There are now no longer any annual plans*, only monthly unless you have a very old plan that is still set to annual payment. If you do not want to add a credit card to your payment information to cover monthly payments, you can try using a gift card to make sure your Apple ID balance has enough money to make payments automatically over a long term. Note that account balance may be used to pay for anything you buy, it won't be reserved for iCloud subscription use exclusively unless you do not buy anything else. Also note though that because this is a subscription, Apple may require a valid payment form such as a credit card be present on the account even though the Apple Account balance will be used first.
*"If you're a new iCloud subscriber, you can only choose a monthly iCloud storage plan."
"This article has been archived and is no longer updated by Apple." Apple usually says that when an article describes a feature or service that Apple no longer supports.
