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

Your bank starts with a nominal interest rate — the base rate it pays you. Then it compounds that rate, meaning it calculates interest on your interest, over the course of a year. The result is your Annual Percentage Yield (APY), which is always higher than the nominal rate because of compounding. Banks must show you the APY, not just the rate, so you can compare accounts honestly across institutions.

The compounding frequency matters. If your bank compounds daily, you earn interest on your interest 365 times a year. If it compounds monthly, only 12 times. Daily compounding produces a higher APY than monthly compounding at the same nominal rate — sometimes by a meaningful amount, especially on larger balances.

The formula banks use is: APY = (1 + r/n)^n − 1, where r is the nominal rate and n is the number of compounding periods per year. You do not need to calculate this yourself — your bank is required to disclose the APY before you open the account — but understanding the formula shows why compounding frequency and rate both matter.

Key Takeaways

  • APY includes the effect of compounding, so it is always equal to or higher than the nominal interest rate your bank advertises.
  • Banks compound interest daily, monthly, or quarterly depending on the account; daily compounding produces the highest APY at the same nominal rate.
  • Your bank must disclose the APY in writing before you open an account, and it must be accurate for the rate period you are offered.
  • APY changes when your bank changes its rate, and the new rate applies only to interest earned going forward, not to money already in the account.

The difference between nominal rate and APY

The nominal rate is what your bank pays per year on your balance. A 4.50% nominal rate means your bank pays 4.50% annually. But that is not what you actually earn, because interest compounds.

If you have $10,000 and your bank compounds interest daily at a 4.50% nominal rate, you do not earn exactly $450 in a year. You earn slightly more, because each day the bank calculates interest on your balance plus the interest you have already earned. That compounding effect is captured in the APY. In this example, the APY would be approximately 4.60%, meaning you earn about $460 instead of $450.

The gap between nominal rate and APY grows larger as rates rise and as compounding happens more frequently. At very low rates, the difference is small enough that you might not notice it. At high rates, it becomes substantial.

How compounding frequency affects your earnings

Compounding frequency is how often your bank calculates and adds interest to your account. The options are daily, monthly, quarterly, or annually. Most savings accounts compound daily, which is why they tend to offer higher APYs than accounts that compound less frequently.

Here is a concrete example. Suppose two banks both offer a 4.50% nominal rate on $10,000. Bank A compounds daily; Bank B compounds monthly. After one year, Bank A's APY is approximately 4.60%, and you earn about $460. Bank B's APY is approximately 4.59%, and you earn about $459. The difference is small on $10,000, but on $100,000 it becomes $10 per year, and on $1 million it becomes $100 per year.

Daily compounding is now standard at most online savings banks. Some brick-and-mortar banks still compound monthly or quarterly, which is one reason online accounts often pay higher APYs. When you compare accounts, always look at the APY, not the nominal rate, because APY already accounts for compounding frequency.

When and how APY changes

Your bank can change the APY on your savings account at any time, with notice. Most banks notify you by email or through your online portal. The new rate applies only to interest earned after the change takes effect — it does not retroactively change interest you have already earned.

APY changes happen most often when the Federal Reserve changes its benchmark interest rate. When the Fed raises rates, banks typically raise APYs on savings accounts within days or weeks. When the Fed cuts rates, banks often cut APYs more slowly, because they want to keep deposits. This is why savings account rates can vary widely between banks even when the Fed rate is the same.

If your bank lowers your APY and you do not like the new rate, you can move your money to another bank. There is no penalty for withdrawing from a savings account, and you can open a new account at a different bank immediately. Some people move their savings every few months to chase the highest available rate.

Why banks disclose APY instead of just the rate

Federal law requires banks to show you the APY because the nominal rate alone is misleading. Two banks might advertise the same nominal rate but compound at different frequencies, resulting in different actual returns. By requiring APY disclosure, the law forces banks to show the true annual return you will receive.

This disclosure appears in the account terms before you open the account, and it must be accurate for the rate period you are offered. If a bank advertises a 4.50% APY and you open the account at that rate, the bank cannot later tell you the APY was actually 4.40%. The rate you see is the rate you get, at least for the promotional period if one is offered.

The APY disclosure also makes it easier to compare accounts across banks. Instead of calculating compounding yourself, you can simply look at the APY and choose the highest one. This transparency is why shopping around for savings accounts is worth your time — the difference between a 4.00% APY and a 4.75% APY is real money.

How to calculate your actual earnings from APY

Once you know the APY, calculating your earnings is straightforward. Multiply your balance by the APY as a decimal. If you have $10,000 at a 4.60% APY, you earn $10,000 × 0.046 = $460 in one year, assuming you do not add or withdraw money.

If you add money during the year, your earnings will be higher, because the new deposits also earn interest. If you withdraw money, your earnings will be lower. Banks calculate interest daily, so every deposit and withdrawal changes your balance and therefore your interest earnings going forward.

Some banks show you projected earnings in your online account. You can also use a savings calculator on your bank's website or a third-party financial site. These tools multiply your balance by the APY and show you what you will earn over different time periods — one month, three months, one year, and so on.

APY on different types of savings accounts

High-yield savings accounts, money market accounts, and certificates of deposit (CDs) all use APY, but the rates differ. High-yield savings accounts typically offer the highest APY among liquid savings products — currently ranging from 4.00% to 5.35% depending on the bank and market conditions. Money market accounts usually pay slightly less, and traditional savings accounts at brick-and-mortar banks often pay 0.01% or less.

CDs lock your money away for a set term — three months, six months, one year, five years — and pay a fixed APY for that entire term. The longer the term, the higher the APY is usually offered, because you are giving the bank more certainty about how long it can use your money. If you withdraw before the term ends, you pay a penalty, which is why CDs are not suitable for money you might need soon.

Interest-bearing checking accounts exist but are rare and usually pay very low APY — often 0.01% to 0.05%. They are not a good place to keep savings. If you want to earn interest, a high-yield savings account or CD is a better choice.

Frequently Asked Questions

Is APY the same as interest rate?

No. Interest rate is the base percentage your bank pays; APY includes the effect of compounding. APY is always equal to or higher than the interest rate. Banks must show you both, but APY is what you actually earn.

Can my APY go down after I open the account?

Yes. Banks can lower APY at any time with notice. The new rate applies to interest earned after the change, not to money already in the account. You can move your money to another bank if you do not like the new rate.

Does APY compound automatically, or do I have to do something?

Compounding happens automatically. Your bank calculates it daily (or monthly, depending on the account) and adds the interest to your balance. You do not have to do anything. The APY shown to you already reflects the compounding that will happen.

Why do online banks pay higher APY than traditional banks?

Online banks have lower overhead costs because they do not operate physical branches. They pass those savings to customers by paying higher APY on savings accounts. They also compete aggressively for deposits because they cannot rely on local customers walking in the door.

If I withdraw money mid-year, do I lose the APY?

No. Your APY does not change if you withdraw. Interest is calculated daily on your current balance, so withdrawals simply reduce the amount earning interest going forward. You keep all interest earned up to the withdrawal date.