If you're on a monthly subscription, your unused credits will roll over and accumulate in your account. However, there is a cap on how many credits can accumulate - you can store up to 2x your monthly credit limit according to your plan.For example, if your plan includes 5,000 credits per month, you can accumulate up to 10,000 credits total.If you have an annual plan instead, the system works differently - you receive all your credits upfront and can use them however and whenever you'd like throughout the year.
Sources:Clay Credits Overview - Clay UniversityFAQ | Clay.comCredit Rollover Monthly vs. Annual Plans