APY (annual percentage yield) is the total interest a savings account, CD, or money market account actually pays you over one year, once compounding is factored in. It’s different from the plain “interest rate,” which only reflects the base rate before compounding is applied. Because U.S. banks and credit unions are required under the Truth in Savings Act to advertise APY rather than just a nominal rate, it’s the number worth comparing when you’re shopping for where to keep your cash.
Here’s a simple example: a bank offers a 4.50% interest rate on a savings account, compounded daily. Because the interest earned each day starts earning its own interest, the APY works out to about 4.60% — higher than the stated 4.50% rate. Put $10,000 in that account and after one year you’d have roughly $10,460, compared to $10,450 if the bank paid the same 4.50% as simple interest just once a year.
The more frequently interest compounds — daily versus monthly versus annually — the larger the gap between the stated rate and the APY. That’s why two accounts advertising the same “interest rate” can pay you different amounts depending on compounding frequency, and why comparing APY, not just the rate, is the more reliable way to compare savings accounts and CDs.
How Compounding Frequency Changes the APY
To see the effect directly, here’s the same 4.50% nominal rate turned into an APY under three different compounding schedules:
| Compounding Frequency | Nominal Rate | Resulting APY |
|---|---|---|
| Annually (once a year) | 4.50% | 4.50% |
| Monthly | 4.50% | ~4.59% |
| Daily | 4.50% | ~4.60% |
Notice the jump from monthly to daily compounding is small compared to the jump from annual to monthly — most of the benefit of more frequent compounding shows up early, which is why daily and monthly compounding accounts often advertise very similar APYs even though “daily” sounds like it should be dramatically better.
Want to see how a rate compounds over a longer stretch than one year? Try our Compound Interest Calculator to run the numbers on your own balance and timeline.
Related Reading
- Where the U.S. Economy Stands in Late 2026 — see how today’s Fed policy and inflation affect what APY is actually worth.
- Is a 4.5% APY on a Savings Account Good Right Now? — a quick answer using the concept explained here.
Official Source and Assumptions
Under Regulation DD (the Truth in Savings Act), administered by the Consumer Financial Protection Bureau, banks and credit unions must disclose the APY using a standardized formula so consumers can compare accounts on an apples-to-apples basis. The examples above assume a fixed rate held constant for a full year; real-world rates on savings accounts and CDs are variable and can change at any time.
FAQ
Is a higher APY always better?
Usually, yes, since APY already accounts for compounding — but also check for balance minimums, monthly fees, and whether the advertised rate is a temporary promotional rate that drops after a few months. A 5.00% APY that reverts to 0.50% after 90 days can end up paying less over a year than a steady 4.50% APY.
Can APY change after I open an account?
Yes. Unlike a CD’s fixed rate, the APY on a standard savings or money market account is usually variable and can rise or fall with market interest rates at the bank’s discretion. CDs typically lock in the APY for the term you choose, which is why locking in a high rate with a CD can make sense when rates are expected to fall.