APR vs APY: The Difference That Costs You Money

Right now, bank websites are full of big numbers. This week, one US bank is advertising 5.00% on savings, another offers 4.50%, and the Federal Reserve has raised its benchmark rate to a 3.75–4.00% range for the first time since 2023. Meanwhile, the average credit card charges about 21.4% in annual interest. Savers are being offered one number, borrowers are being quoted another — and both end in "%," which makes them easy to confuse.

Here is the problem: a 5% APY and a 5% APR are not the same number. They measure different things, and mixing them up quietly changes what you actually earn — or what you actually pay.

What APR really means

APR stands for annual percentage rate: the simple, annualized interest rate on money, as if no compounding happened during the year. It is the number you see on borrowing products — credit cards, auto loans, and mortgages in the US.

The key word is simple. A 12% APR does not mean 12% added to your debt once a year. Most lenders compound far more often — daily, for most US credit cards. The card takes the APR, divides it by 365, and applies that sliver to your balance each day; the next day, it charges interest on the new, slightly larger balance. The APR names the nominal yearly rate; it hides the compounding running underneath.

That gap matters. With the average US card APR at about 21.4% (per the Fed's October 2026 consumer-credit data), daily compounding means a balance carried for a full year actually grows by roughly 23.9% — more than the advertised rate. The APR is the starting price of borrowing, not the final bill.

The APR tells you the nominal yearly rate. On a credit card, interest compounds daily — and the difference is the real cost.

What APY really means

APY stands for annual percentage yield. Unlike APR, it bakes compounding into the number. When a savings account advertises 5.00% APY, that is the actual growth of your balance in a year, assuming you leave the money alone and the rate does not change. The formula is APY = (1 + r ÷ n)ⁿ − 1, where n is how many times a year it compounds.

So a 10% nominal rate compounded monthly becomes about 10.47% APY — $1,000 left alone ends the year at roughly $1,104.71, not $1,100. At low rates the difference is cosmetic; at higher rates, or over many years, it is real money. This is also why US deposit accounts must quote APY: it lets you compare two accounts with different compounding schedules at a glance.

Same rate, different acronym: the worked numbers

Nominal rate & compounding	If quoted as APR (borrow)	If quoted as APY (save)
5% compounded monthly	Costs 5% nominal; true cost a touch higher	5.12% APY — $10,000 → $10,511.62 in a year
10% compounded monthly	Costs 10% nominal; true cost higher	10.47% APY — $1,000 → $1,104.71
12% compounded daily	True cost ≈ 12.75%	12.75% APY
21.4% compounded daily (card)	Avg US card APR ≈ 23.9% effective cost	—

Notice the direction of the advantage. On the savings side, compounding works for you: APY is always equal to or higher than the nominal rate (equal only with annual compounding). On the borrowing side, it works against you: a 21.4% APR silently becomes a 23.9% effective cost. The acronym tells you which side you are on.

Where each one shows up

Product	You will see	What to remember
Savings accounts, CDs	APY (US)	The actual yearly growth, fees aside
Credit cards, auto loans, mortgages	APR (US)	The nominal rate; true cost is higher with frequent compounding
UK savings accounts	AER (Annual Equivalent Rate)	The UK's equivalent of APY — compounding included, built for comparisons
UK loans, credit cards	APR	Must include fees and charges, reflecting the fuller cost of borrowing

UK readers rarely meet the letters APY, but they already know the concept: AER does the same job. MoneySavingExpert's classic example makes it concrete — a UK account paying a 4.89% "gross" rate monthly ends the year with exactly the same money as one paying 5% annually, and both quote an AER of 5%. The gross rate is the flat payout; the AER is the honest comparison number. So in the UK: compare AER with AER.

One more nuance: a US mortgage's APR is deliberately higher than its "note rate" because it folds in most lender fees — that is what makes APR useful for comparing loan offers. A credit card's APR, though, usually covers only the interest on balances; the annual fee is disclosed separately. Always read the fee schedule alongside the rate.

Four ways people get caught out

1. Chasing a headline APY without reading the conditions. That 5.00% offer may require a linked checking account, monthly direct deposits, or cap the balance earning the top rate — as this week's top US offers do. Compare conditions, not just numbers.
2. Thinking the card's APR is the whole story. At 21.4% APR with daily compounding, the effective yearly cost is nearly 24%. Minimum payments stretch that compounding over years — and the APR figure alone never warns you.
3. Assuming a variable APY is locked in. APY assumes the rate stays constant for a full year. In a hiking cycle like this one, variable rates often rise; when cuts return, they fall just as fast.
4. Ignoring fees and taxes. Both figures describe interest, not the net result. Maintenance fees drag returns down, an annual fee adds to borrowing cost, and interest income is taxable outside sheltered accounts like UK Cash ISAs.

A 4% APY is a promise about what you keep. A 4% APR is a down payment on the real cost. Same number, opposite meanings.

Frequently asked questions

Which matters more: a high APY or a low APR?

Both, in their own lanes. If you carry debt, the lowest APR matters most — every point off compounds in your favor. If you hold savings, the highest APY matters most. They do not compete because one prices borrowing and the other prices saving.

Can APY ever be lower than the nominal rate?

No. With compounding once a year or more, APY is always equal to or higher than the nominal rate — exactly equal only when interest is added once a year. The gap widens with higher rates and more frequent compounding.

Why does my UK account say AER instead of APY?

AER (Annual Equivalent Rate) is the UK's standardized savings figure and works the same way as APY: it includes compounding so accounts can be compared directly. UK banks must show it next to every advertised savings rate.

Does APR include fees?

It depends. On US mortgages, APR folds in most lender fees — which is why it exceeds the note rate. On US credit cards, the APR typically covers interest on balances only, with annual fees disclosed separately. In the UK, advertised APR on credit must include fees and charges. Always check the fine print.

Your next step

Open your savings account page and your latest card statement side by side. Note which acronym each uses and the compounding frequency in the fine print, then run one comparison: your APY against one competing account, and your card's APR against its ~23.9% effective cost. Ten minutes reading the small letters is the cheapest interest-rate education there is — and with rates moving, it pays more than usual.