APY is calculated by taking your interest rate, compounding it over the year, and showing you the total return as a percentage

Your bank takes the annual interest rate it offers, factors in how often it compounds (daily, monthly, or quarterly), and converts that into a single number called APY — Annual Percentage Yield. That number tells you what percentage of your balance you'll earn over a full year if you don't touch the money. The math matters because a savings account that compounds daily will earn you more than one with the same stated rate that compounds monthly, even though the difference looks small on paper.

The formula banks use is: APY = (1 + r/n)^n − 1, where r is the annual interest rate and n is how many times per year the interest compounds. You don't need to do this math yourself — your bank is required to show you the APY before you open the account — but understanding what's happening behind the number helps you compare accounts honestly.

Key Takeaways

  • APY includes the effect of compounding, so it's always equal to or higher than the stated interest rate.
  • Daily compounding earns more than monthly or quarterly compounding at the same interest rate, because your interest starts earning interest more often.
  • Banks must disclose the APY in writing before you open an account, so you can compare savings accounts side by side using that number alone.
  • The difference between a 4.50% APY account and a 4.25% APY account compounds over time — on $10,000, that's roughly $25 to $30 more per year.

How compounding frequency changes your earnings

Compounding is the engine that makes APY different from the base interest rate. When your bank compounds interest daily, it calculates what you've earned overnight, adds it to your balance, and then calculates tomorrow's interest on that larger number. That means your interest earns interest. With monthly compounding, the bank waits 30 days before adding earned interest back into your balance, so your money has fewer chances to compound.

Take a $10,000 balance at a 4.00% annual interest rate. With daily compounding, you'd earn roughly $408 over the year. With monthly compounding at the same 4.00% rate, you'd earn about $407. The difference is small in dollar terms, but it compounds — literally — over years and across larger balances. Most savings accounts today compound daily, which is why you'll see APY figures that are slightly higher than the stated rate.

Why APY matters more than the interest rate alone

The interest rate is what the bank advertises; the APY is what you actually earn. A bank might advertise "4.00% interest" but show you an APY of 4.08% because of daily compounding. When you're comparing two savings accounts, always use the APY number, not the interest rate. The APY is the honest comparison because it already includes compounding.

This becomes important when you're choosing between accounts at different banks. One bank might offer 4.50% APY with daily compounding. Another offers 4.50% APY with monthly compounding. The APY is the same, so your earnings will be the same — the compounding frequency is already baked into that number. But if one bank shows you 4.50% APY and another shows 4.48% APY, the first bank will earn you more money, period.

What happens to APY when interest rates change

Banks adjust APY when the Federal Reserve changes interest rates or when they decide to change their own rates. If you have a savings account at a traditional bank, your APY can go down without warning — and often does when the Fed cuts rates. High-yield savings accounts (HYSAs) at online banks tend to adjust faster in both directions because they're competing for deposits and respond quickly to market changes.

Your bank must notify you before lowering your APY, usually by email or through your online account. The notification typically gives you a grace period — often 30 days — before the new rate takes effect. You can then decide whether to move your money to a different bank offering a higher APY. This is why checking your account's current APY every few months makes sense, especially if you have a large balance.

How to find and compare APY across accounts

Your bank shows the APY in the account disclosure document, which you receive before opening the account. Online, it's usually listed right next to the account name on the bank's website. For savings accounts, look for the APY figure in the account details or rates page — it will be a single percentage number, often highlighted because it's the main selling point of the account.

When comparing accounts at different banks, write down the APY for each one and the minimum balance required to earn that rate. Some banks offer a higher APY only if you maintain a certain balance; if your balance drops below that threshold, the APY drops too. The disclosure document will spell out these conditions. Once you have the APY and the balance requirement, you can compare directly — the account with the highest APY that you can meet the balance requirement for is the one that will earn you the most money.

The relationship between APY and your actual earnings

To calculate how much you'll earn in a year, multiply your balance by the APY expressed as a decimal. A $25,000 balance at 4.50% APY earns $1,125 over the year (25,000 × 0.045 = 1,125). That assumes you don't add or withdraw money during the year. If you deposit more money partway through the year, that new deposit earns interest for only part of the year, so your total earnings will be higher but the calculation becomes more complex.

Banks calculate interest daily but usually credit it monthly or quarterly. You'll see the interest appear in your account on a regular schedule — check your account statement to see when. The interest is yours to keep; you don't have to do anything to receive it. If you withdraw money before the interest is credited, you lose the interest that would have been earned on that withdrawn amount for the period it was in the account.

Why different banks show different APYs for the same account type

Banks set their own APY based on how much they need deposits and what they can afford to pay. Online banks typically offer higher APYs than brick-and-mortar banks because they have lower overhead costs and compete primarily on rate. A traditional bank might offer 0.01% APY on savings while an online bank offers 4.50% APY on the same type of account. Both are real; the difference reflects their business models and competitive positions.

APY also varies based on the account type. Money market accounts sometimes offer slightly higher APY than savings accounts. Certificates of Deposit (CDs) offer fixed APY for a set term — usually higher than savings accounts because your money is locked up. Checking accounts rarely earn meaningful APY, though some banks offer small rates on checking balances. The account type, the bank's strategy, and current market conditions all affect what APY you'll see.

Frequently Asked Questions

Is APY the same as interest rate?

No. The interest rate is the base percentage the bank pays; APY includes the effect of compounding. APY is always equal to or higher than the interest rate. When comparing accounts, use APY because it shows your actual earnings.

Can APY go down after I open an account?

Yes. Banks can lower APY at any time, though they must notify you first, usually with 30 days' notice. You can then move your money to a different bank if the new rate is too low. APY on CDs is locked in for the term, so it won't change.

How often is interest compounded?

Most savings accounts compound daily, some monthly or quarterly. Daily compounding earns slightly more than monthly or quarterly at the same rate. The APY already reflects the compounding frequency, so you don't need to calculate it yourself — just compare APY numbers.

What's the difference between APY and APR?

APY is for savings and shows what you earn; APR is for loans and shows what you pay. APY includes compounding; APR typically does not. When saving, look for APY. When borrowing, look for APR.

Do I need a minimum balance to earn the advertised APY?

Sometimes. Check the account disclosure document before opening. Some banks require a minimum balance to earn the full APY; if your balance drops below that, your APY drops too. Other banks have no minimum. The disclosure will state the requirement clearly.