The interest-free period on a credit card between a purchase and its payment due date is called a grace period.
A grace period gives a cardholder time to pay the statement balance without purchase interest being added. It usually runs from the end of a billing cycle, when transactions are compiled into a statement, to the payment due date.
The length varies by issuer and card, but credit-card grace periods commonly span about 20 to 55 days. They generally apply only when the cardholder pays the required balance in full and on time. Carrying an unpaid balance can cause new purchases to accrue interest immediately.
A billing cycle is the period in which transactions accumulate; it is not itself the interest-free period. Cash advances also commonly lack a grace period, with interest beginning when the cash is withdrawn.