Go to account.fieldmargin.com/billing and click the farm you want to view from your active subscription list. On the farm details screen you will be able to see the next billing date.

To check when you next billing date for subscriptions paid for via Apple in-app purchases, follow the instructions in this Apple support article:

https://support.apple.com/en-gb/HT204088

To check when you next billing date for subscriptions paid for via Google Play Store in-app purchases, follow the instructions in this Google support article:

https://support.google.com/googleplay/answer/7018481?hl=en-GB&co=GENIE.Platform%3DAndroid