What happens if I don't use all my credits before the end of the month?

You lose nothing at your renewal. Unused credits roll over and stay valid for a while after they are granted:

• Monthly plan — credits are valid for 2 months from the day they are granted
• Yearly plan — credits are valid for 13 months from the day they are granted

So a quiet month on a monthly plan is not wasted: those credits stay spendable through the following cycle, on top of the new ones you receive. In effect, you get one extra month past your renewal date to use them.

Check your current balance at any time from Billing & plans.