Explainer. Three letters on your card statement, three on your savings account, and one of them is costing you money right now. Updated September 5, 2026.
APR and APY look like the same idea wearing different hats. They are not. One is the price you pay to borrow, quoted before compounding. The other is what a bank pays you, quoted after it. Read them as interchangeable and you will misjudge both sides of your own balance sheet.
APR: a number quoted by the year, charged by the day
APR is the annual percentage rate, and on a credit card it is the interest stated as a rate for a year. The mechanism underneath is daily. The CFPB describes the daily periodic rate as the number used to calculate interest by multiplying it against what you owe at the end of each day, and it is found by dividing the APR by 360 or 365, depending on the issuer.
Put numbers on it. A 24.99 percent APR is a daily rate of about 0.0685 percent. Carry $3,000 for a year and simple arithmetic says $750 of interest. Because yesterday's interest joins today's balance, the real figure lands closer to $850. The compounding you want on your savings is working against you here.
The grace period that makes your APR irrelevant
An APR you never pay is a number on a page. The CFPB defines the grace period as the stretch between the end of a billing cycle and the date your payment is due, and card issuers must get the bill to you at least 21 days before that date. Pay the statement balance in full inside that window and purchases cost you nothing, whatever the APR says.
Lose it and the rule changes: interest is charged on the unpaid portion, and on many cards new purchases start accruing from the day they post until you are back to a zero balance. That is the single most expensive line in consumer credit, and it turns on one decision each month.
APY: the number that already did the math
APY is the annual percentage yield. Regulation DD, the rule behind the Truth in Savings Act, is why every bank quotes deposits this way, and the yield already contains the compounding. Put $10,000 into a certificate paying 4.35 percent APY and you have $10,435 in a year. Nothing left to calculate.
That is the practical value of the letters: two savings accounts quoting the same APY pay the same, no matter how one compounds each day and the other each quarter. Comparison is honest by regulation. Card APRs are disclosed under Regulation Z, which governs the boxes on a card agreement, and those are quoted without compounding.
Why your card rate moves without a letter from the bank
Most cards carry a variable APR written as prime plus a margin. Prime is the bank prime loan rate the Federal Reserve publishes in the H.15 release, and it sat at 6.75 percent as of the release dated September 4, 2026. A card at prime plus 18.24 is a card at 24.99 percent today, and it will be a card at 25.24 percent the month after prime rises a quarter point.
Your savings rate reacts to the same move in the opposite direction, and slower. Banks pass a cut through in days and a rise through in weeks. That lag is why the gap between the best and the average account is so wide: the FDIC national average for a 12 month certificate was 1.71 percent as of August 17, 2026, while online banks were paying above 4 percent for the same term.
What not to do
- Do not compare a card APR to a savings APY and conclude the spread is your cost. They are measured on different bases before you start.
- Do not carry a balance to build credit. Utilization is read from the reported balance, not from interest paid.
- Do not treat a 0 percent intro APR as free money without reading the balance transfer fee and the date the promotion ends. The fee is charged up front.
- Do not chase a headline APY without the minimum balance, the monthly fee and the "as of" date next to it. A rate from March is not a rate.
What to do this week
- Open your card agreement and find the purchase APR. If it reads "prime plus" something, add 6.75 and you have today's rate.
- Divide that APR by 365. Multiply by the balance you carry. That is what one day of not paying costs you.
- Compare your savings APY against the current table on Banrox bank rates and against the FDIC average. If your bank is under 1 percent, the gap is the price of staying.
- Run both numbers through the compound interest calculator before you move money, and check the institution in the bank directory.
Both sides of the rate in one place. Banrox tracks card APRs in the marketplace and deposit APYs on the rates page, each with the date it was checked, so you are comparing today's numbers and not last quarter's. Start with the free plan.
Sources
- CFPB: What is a credit card interest rate? What does APR mean?
- CFPB: What is a daily periodic rate on a credit card?
- CFPB: What is a grace period for a credit card?
- Federal Reserve H.15: Selected Interest Rates, bank prime loan rate
- FDIC: National Rates and Rate Caps
- 12 CFR Part 1030 (Regulation DD, Truth in Savings)
- 12 CFR Part 1026 (Regulation Z, Truth in Lending)
Educational content, not financial or legal advice. Rates move: prime, the FDIC averages and every bank offer above carry the date they were checked, and they will be different by the time you read this.
