In the mobile app, you can tap on the Credits button to see 2 important things.
When you will receive your next credits
Your history of how your credits have been used
Credit Summary
Tells you how many available, monthly, and bonus credits you have.
You get 2 monthly credits on the same day each month.
You can roll over up to 6 monthly credits before they start to expire.
Bonus credits do not count toward that roll over limit. In my example below, I could roll over 4 more monthly credits.