A credit card can be used without paying interest, but only under a condition many holders discover after it has lapsed. The grace period applies to purchases and depends on the balance being cleared in full.
The period covers the gap between purchase and due date
Purchases made during a statement cycle are not charged interest until the payment due date, which typically falls a few weeks after the cycle closes.
The window between the earliest purchase and that date can therefore extend well beyond a month, which is where the interest-free borrowing arises.
The card issuer funds that period, and interchange revenue is part of what pays for it.
The condition is full payment, not minimum payment
Grace applies only where the previous statement balance was cleared entirely. Paying the minimum, or anything short of the full amount, generally forfeits it.
Once forfeited, interest is charged on new purchases from the transaction date rather than from the due date, with no interest-free window at all.
This is the mechanism by which a single partial payment can change the cost of everything subsequently bought on the card.
Restoring the grace period takes more than one payment
Issuers commonly require the balance to be cleared in full and, in many cases, to remain clear for a further cycle before the interest-free treatment resumes.
A cardholder who clears a balance may therefore still be charged interest on the following month's purchases.
The requirement is set out in the account terms and varies between issuers, which is why the experience differs between apparently similar products.
Some transactions never receive grace
Cash advances and cash-equivalent transactions typically accrue interest immediately, often at a higher rate and usually with a separate fee.
Balance transfers are treated under their own terms, which may offer a promotional rate for a set period but rarely a grace period.
Because these balances sit alongside purchases in the same account, the effective cost of the account depends on its composition rather than a single headline rate.
Residual interest appears after the balance is cleared
Interest accrues daily, so paying off a statement balance still leaves interest accrued between the statement date and the payment date.
That amount appears on the following statement, which surprises holders who believed the account had been settled fully.
Clearing it promptly avoids further accrual, and requesting a payoff figure rather than paying the statement balance is the way to close an account cleanly.