Can I buy iCloud storage year-to-year instead of monthly basis?

Only by using Apple ID balance to prepay it; click here and see what options are available in your country. It'll be applied first whenever allowed, not just for the subscription.

If you use gift cards, buy them in advance and redeem them just before the payments come due.

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Nursejilly wrote:

Can I buy extra cloud storage just once? Not pay monthly

No: space on iCloud - as on any online service - is rented, not purchased. Bur see above for a way of paying for a year in one go.

No

Can I buy extra cloud storage just once? Not pay monthly

You can rent storage for a month if you purchase it and then downgrade before it renews.