APY is calculated by taking your annual interest rate and compounding it daily, weekly, or monthly—whichever schedule your bank uses—then expressing the result as a single yearly percentage.
The formula banks use is: APY = (1 + r/n)^n − 1, where r is the annual interest rate and n is the number of times interest compounds per year. If your bank compounds daily (n = 365), you earn interest on your interest 365 times a year. If it compounds monthly (n = 12), you earn it 12 times. The more often interest compounds, the higher your APY becomes, even if the base rate stays the same.
Banks must disclose the APY, not just the interest rate, because APY shows you the real return you'll get. A savings account with a 4.50% annual rate compounded daily will deliver a higher APY than one with 4.50% compounded monthly. The difference is small but real—and it adds up over time, especially on larger balances.
Key Takeaways
- APY includes the effect of compounding, so it is always equal to or higher than the stated annual interest rate.
- Daily compounding produces a higher APY than monthly or quarterly compounding at the same base rate.
- Banks must show you the APY before you open an account, usually in the account disclosures or rate sheet.
- A difference of 0.25% APY on a $10,000 balance adds up to $25 per year in extra earnings.
Why compounding frequency matters
Compounding is when your interest earns interest. On day one, the bank calculates interest on your principal balance. On day two (or the next compounding date), it calculates interest on your principal plus the interest you just earned. That cycle repeats.
If your bank compounds daily, this happens 365 times a year. If it compounds monthly, it happens 12 times. The more frequently interest compounds, the more times your earnings get added back to your balance and earn interest themselves. Over a year, daily compounding can add 0.10% to 0.20% to your APY compared to monthly compounding, depending on the base rate.
Most high-yield savings accounts compound daily. Traditional savings accounts at brick-and-mortar banks often compound monthly or quarterly. Check your account disclosure to see which schedule applies to you.
The difference between APY and the annual interest rate
The annual interest rate (sometimes called the nominal rate or stated rate) is the base percentage your bank pays. The APY is what you actually earn after compounding is factored in. They are the same number only if interest compounds once per year, which almost never happens.
Example: A savings account offers a 4.50% annual interest rate compounded daily. The APY will be approximately 4.60%. You earn the extra 0.10% purely from compounding. On a $50,000 balance, that difference is about $50 per year.
Banks are required by federal law (Regulation DD) to show you the APY in writing before you open an account. This makes it easier to compare accounts across different banks, because you are comparing the same metric—the real return you will receive.
How to find the APY for your account
Your bank must disclose the APY in the account agreement, on the rate sheet, or on the account details page of your online banking portal. Look for the label "Annual Percentage Yield" or "APY"—not "annual interest rate" or "interest rate".
If you are shopping for a new account, most banks display the APY prominently on their website or in their rate comparison tool. Some banks show both the annual interest rate and the APY side by side so you can see the compounding effect. If you cannot find the APY, call the bank or ask in writing—they are legally required to provide it.
The APY you see advertised is the rate for new deposits made today. If you opened an account months ago, your rate may be different. Banks can change rates at any time, and they often lower rates when the Federal Reserve cuts rates. Check your account statements or log into your online banking to see your current APY.
What happens when rates change
Banks adjust savings account rates frequently, especially high-yield accounts. When the Federal Reserve raises its benchmark rate, banks typically raise APYs to attract deposits. When the Fed cuts rates, banks lower APYs, sometimes within days.
Your bank must notify you before lowering your rate, usually by email or through your online banking portal. The notice typically gives you a window (often 30 days) to review the change. You cannot stop the rate from dropping, but you can move your money to another bank if the new rate no longer meets your needs.
The APY you locked in when you opened the account does not stay locked. It changes with your bank's rates. Only certificates of deposit (CDs) lock in a fixed rate for a set term.
How to use APY to compare accounts
When comparing savings accounts, always compare APYs, not interest rates. A bank advertising a 4.75% APY is offering you more than one advertising a 4.75% annual rate compounded monthly, even though the numbers look the same.
Use the APY to calculate how much you will earn. Multiply your balance by the APY, then divide by 12 to get your approximate monthly earnings. On a $25,000 balance at 4.60% APY, you earn roughly $96 per month. On the same balance at 4.25% APY, you earn roughly $88 per month—an $8 monthly difference that adds up to $96 per year.
Small differences in APY matter most on large balances or over long holding periods. On a $1,000 balance, the difference between 4.25% and 4.60% is about $3.50 per year. On a $100,000 balance, it is $350 per year. If you are holding the money for five years, that gap widens significantly.
Why your actual earnings might differ from the APY
The APY shown to you is an estimate based on the assumption that your balance stays the same and the rate does not change. In reality, your earnings will differ if you deposit or withdraw money during the year, or if the bank changes the rate.
If you deposit $10,000 in month six, you do not earn the full APY on that $10,000 for the entire year—only for the months it sits in the account. If the bank lowers the rate in month nine, your earnings for months nine through twelve will be lower than the APY suggested.
Banks calculate interest based on your daily balance, so deposits and withdrawals affect your earnings immediately. Some banks also have minimum balance requirements; if your balance drops below the minimum, you may earn a lower rate or no interest at all. Check your account agreement for these details.
Frequently Asked Questions
Can I calculate APY myself if I only know the annual interest rate?
Yes, using the formula APY = (1 + r/n)^n − 1. If your bank offers 4.50% compounded daily (n = 365), the calculation is (1 + 0.045/365)^365 − 1, which equals approximately 0.0460 or 4.60% APY. A calculator makes this easier, but your bank should provide the APY for you.
Is a higher APY always better?
Yes, if all other account features are equal. A 4.75% APY is better than 4.50% APY. However, also check for monthly fees, minimum balance requirements, and withdrawal limits. A high APY with a $25,000 minimum balance or a $10 monthly fee may not be worth it if you have a smaller balance or need frequent access.
Does APY change if I leave my money in the account longer?
No. APY is an annual rate, so it does not increase just because you hold the money for two years instead of one. However, your total earnings do increase because you earn interest on a larger balance (your original balance plus accumulated interest). This is the power of compounding over time.
What is the difference between APY and APR?
APY is used for savings and deposit accounts; it includes compounding. APR (Annual Percentage Rate) is used for loans and credit cards; it does not include compounding in the same way. APR shows the cost of borrowing, while APY shows the return on saving.
If my bank compounds daily, do I see interest added to my account every day?
No. Daily compounding means the bank calculates and adds interest to your balance daily, but most banks only show the total interest once per month on your statement. The daily compounding is happening behind the scenes, even if you do not see it reflected daily in your account.