Interest on a credit card starts accruing the day after your payment due date whenever you don’t pay the full statement balance. Pay the statement in full by the due date and you owe no interest on ordinary purchases. Two categories break that rule: cash advances and balance transfers begin generating interest the moment they post, with no grace period at all.
The Grace Period Is What Keeps Interest at Zero
The grace period is the stretch between the close of your billing cycle and your payment due date. Pay the full statement balance during that window and new purchases cost you nothing beyond their sticker price. Federal law does not require card issuers to offer a grace period, but most do, and when they do, the Credit CARD Act of 2009 requires them to mail or deliver your statement at least 21 days before the due date.1Office of the Law Revision Counsel. 15 USC 1666b – Timing of Payments2Consumer Financial Protection Bureau. What Is a Grace Period for a Credit Card?
The protection is all-or-nothing. Pay a dollar less than your statement balance and the grace period disappears. Once it’s gone, you typically have to pay the statement balance in full for two consecutive billing cycles before it comes back. In the meantime, every new purchase starts accruing interest the day it posts.
What Changes the Moment You Carry a Balance
If you leave any part of the statement balance unpaid past the due date, interest applies to whatever remains, and it accrues daily from that point on. Because you’ve also lost the grace period, new purchases in the current cycle start accruing interest from their posting date rather than from the end of the cycle. The old carried balance and every fresh charge start compounding at the same time.
There’s a wrinkle that catches people trying to zero out a card. It’s called residual interest, sometimes trailing interest. Your statement shows the balance as of the day it was generated, but interest keeps accruing daily until your payment actually posts. Pay a $2,000 statement ten days later and roughly ten days of interest have piled up since the statement printed. That leftover shows up on the next bill even though you thought the account was clear. Paying that small remaining amount on the follow-up statement is what actually closes it out.
Transactions With No Grace Period
Some transactions never qualify for a grace period, even on an account that’s paid in full every month. Interest on these starts the day they post.
Cash Advances
ATM withdrawals on a credit card, money orders bought with the card, and convenience checks tied to the card account are all cash advances. Interest begins on the transaction date. The rate is also higher: as of early 2026, purchase APRs at major issuers ran roughly 16% to 22% while cash advance APRs ran about 18% to 32% depending on the issuer. A separate transaction fee, commonly 3% to 5% of the amount, applies on top.
Balance Transfers
Moving debt from one card to another works the same way by default: interest accrues from the transfer date. What changes the math is a promotional 0% offer. During a promotional window, no interest accrues on the transferred amount. When the promo ends, the standard balance transfer rate takes effect immediately on whatever remains. Transfer fees typically run 3% to 5%, and the promotional length varies, so the card agreement is worth reading before you move a balance.
How the Daily Calculation Works
Most credit card rates are variable and tied to the U.S. prime rate, which sat at 6.75% as of February 2026.3Board of Governors of the Federal Reserve System. H.15 – Selected Interest Rates (Daily) Your card’s APR is prime plus a fixed margin the issuer sets based on your credit profile. When the Federal Reserve moves its benchmark, the prime rate follows and your card rate adjusts, usually within one to two billing cycles.
To convert that annual rate into what you actually owe each day, the issuer divides the APR by 365 (some use 360). A 24% APR becomes a daily periodic rate of about 0.0657%. Federal disclosure rules require your APR and the balance calculation method to appear on every statement and in your card agreement.4eCFR. 12 CFR Part 1026 Subpart B – Open-End Credit
Most issuers use the average daily balance method. Each day of the cycle, the issuer records your outstanding balance. At the end of the cycle, those daily balances are added together, divided by the number of days in the cycle, and the result is multiplied by the daily periodic rate and then again by the number of days in the cycle to produce the month’s interest charge. Because every day counts, paying down part of a balance early in the cycle reduces the interest for the rest of it, and a large purchase early in the cycle sits in the calculation longer than one made near the end. On a flat $5,000 balance at 24% APR over a 30-day cycle, daily interest is roughly $3.29, or about $98.63 for the month.
Deferred Interest Promotions Can Retroactively Start From Day One
Retail store cards and some general-purpose cards advertise “no interest if paid in full” deals, commonly for 6, 12, or 18 months. These deferred interest plans are not the same as a true 0% APR. With a real 0% offer, any leftover balance simply starts accruing going forward when the promo ends. With deferred interest, if any part of the promotional balance is still there at the deadline, the issuer charges every dollar of interest that would have accrued since the original purchase date.5Consumer Financial Protection Bureau. I Got a Credit Card Promising No Interest for a Purchase if I Pay in Full Within 12 Months – How Does This Work?
Buy a $2,000 appliance on a 12-month deferred plan at 28% APR and finish the year still owing $100, and the interest owed isn’t calculated on that $100. It’s roughly 12 months of interest on the full $2,000, potentially $500 or more, billed all at once. Falling more than 60 days late on a minimum payment during the promo period can trigger the same result. Federal rules require the payoff deadline to be shown prominently on each statement during the promotion.4eCFR. 12 CFR Part 1026 Subpart B – Open-End Credit
When a Penalty Rate Can Take Over
Falling behind can push your account to a penalty APR, which can reach 29.99% or higher. In your first year with a card, the issuer generally can’t raise your rate except in narrow circumstances, one of which is being more than 60 days past due.6eCFR. 12 CFR 1026.55 – Limitations on Increasing Annual Percentage Rates, Fees, and Charges After the first year, the issuer can raise rates with 45 days’ advance notice, but the new rate can’t be applied to balances that existed before the notice.
The 60-day delinquency trigger is the exception that lets the penalty rate apply to your existing balance rather than only new charges. Once it’s imposed, the issuer must review the increase no later than six months after your sixth payment following the change, and reduce the rate if the factors that prompted it have improved.7Consumer Financial Protection Bureau. Regulation Z – Section 1026.59 Reevaluation of Rate Increases In practice, the penalty rate sticks around for at least six months even after payments are back on track.