Credits refresh each month. On paid plans, unused credits carry over; on Free they do not.
Monthly reset
Your credit allowance refreshes at the start of each calendar month.
Rollover on paid plans
On Starter, Professional, and Enterprise, unused credits carry over to the next month, so a quiet month is never wasted. Usage This Month shows them as carried over credits.
Free plan
Unused Free plan credits do not carry over.
Changing plans
When you change plans, your unused credits come with you. Credits from Pay As You Go packs and gift codes are added to your balance and never expire.