Apple care + and how many months are covered after 12 payments

If you are paying for Applecare + monthly, the term is for the month you are paying for.It will renew automatically. For single payment plans, the initial coverage period is 2 years. Here are the US terms:

https://www.apple.com/legal/sales-support/applecare/applecareplus/docs/applecareplusnaen.html

https://www.apple.com/support/products/iphone/

It will have covered the 12 months you've paid for.

Each payment covers the month in which you are paying it.