For Google Play Store credit that does expire, how does one see when it expires?
For credits that do not expire, see this QA.
Android Enthusiasts Stack Exchange is a question and answer site for enthusiasts and power users of the Android operating system. It only takes a minute to sign up.Sign up to join this community
If you go to Google Wallet payment methods you can see your Google Play credit, how much has an expiry date and when it expires.
FAQ says it expires 1year after the date of your most recently completed survey