Two savings accounts can advertise the same interest rate and still pay you different amounts over a year. The reason is compounding, and the number that captures it is the annual percentage yield, or APY. When you are comparing places to park cash, the APY — not the plain interest rate — is the honest figure, and it is the one worth reading first.
Understanding the gap between the two takes only a minute, and it stops you from being fooled by a headline rate that leaves out half the story.
What each number means
The interest rate (sometimes called the nominal rate) is the base rate the bank applies to your balance before compounding is taken into account. The APY is what you actually earn in a year once that interest is compounded and starts earning interest of its own.
Because interest earns interest, the APY is always equal to or greater than the stated rate — never lower. A 5% rate that compounds monthly works out to an APY a little above 5%. If a rate and its APY are listed as identical, the account compounds annually, and there is no hidden boost to find.
The interest rate is the promise; the APY is the delivery. Compare savings accounts on APY and you are comparing what lands in your pocket, not what fits in an ad.
Why frequency matters less than you think
Compounding more often does raise the yield, but the effect shrinks fast. Going from annual to monthly compounding moves the needle noticeably; going from monthly to daily barely registers. On a 5% account, the difference between daily and monthly compounding is a rounding error over a year.
The practical lesson: do not agonize over compounding frequency. A higher rate at a lower frequency almost always beats a lower rate compounded more often. Chase the rate first; the APY already bakes the frequency in.
- Same rate, different frequency: the more frequent one wins, but only slightly.
- Different rate, different frequency: compare APYs and take the higher one — the math is already done for you.
A quick way to picture it
Imagine two accounts, both advertising a 5% rate. The first credits all the interest once, at year end. The second credits a twelfth of it each month, and each month’s interest immediately starts earning too. By December, the second account has been earning interest on interest for most of the year, so it finishes slightly ahead — its APY is a touch above 5%, while the first account’s APY is exactly 5%.
That small gap is the entire idea behind APY. It is not a different rate so much as an honest accounting of what the same rate produces once compounding is included. The larger your balance and the longer you leave it, the more that accounting matters — which is why the figure earns its place at the top of any comparison.
Using APY to compare accounts
In the US, the Truth in Savings Act requires banks to disclose APY, which is precisely so you can line up offers on equal terms. When you shop, read the APY, confirm whether it is a promotional rate that expires, and check for balance tiers or minimums that change what you actually earn.
The same logic runs in reverse on the borrowing side. There, the comparable all-in figure is APR, which folds fees into a loan’s cost. Yield or cost, the principle holds: the number that includes the extras is the one that tells the truth.