Banks pay interest by calculating a percentage of your account balance and depositing that amount into your account on a set schedule

The bank takes the money you deposit, lends it out to other customers as mortgages, car loans, and business loans, and keeps the difference between what it pays you and what borrowers pay it. That difference is how the bank makes money. The interest rate you receive — called the Annual Percentage Yield (APY) — is what the bank offers to let it use your money. Banks are required to tell you the APY before you open an account, and it determines exactly how much you will earn.

The actual deposit into your account happens on a schedule set by the bank. Most banks compound interest daily, meaning they calculate what you owe interest on each day, then add that interest to your balance. That new balance becomes the base for the next day's calculation. Some banks compound monthly or quarterly instead. The more often interest compounds, the more you earn, because you earn interest on your interest.

Key Takeaways

  • Your bank calculates interest as a percentage of your balance and deposits it into your account on a schedule — usually monthly, but sometimes daily or quarterly.
  • The Annual Percentage Yield (APY) is the rate the bank advertises, and it already accounts for how often the bank compounds interest, so you can compare rates directly between banks.
  • Interest compounds when the bank adds earned interest to your balance, then calculates the next period's interest on that larger amount.
  • Banks pay lower rates on regular savings accounts and higher rates on money market accounts and certificates of deposit (CDs), because those accounts tie up your money longer or require higher balances.
  • Your interest earnings are taxable income, and the bank will send you a 1099-INT form if you earn $10 or more in a year.

How the APY determines what you actually earn

The APY is an annual rate, but banks do not wait a full year to pay you. If your account earns 4.50% APY, the bank divides that by the number of times it compounds per year, then deposits that portion into your account on each compounding date. A bank that compounds daily divides 4.50% by 365, calculates interest on your balance for that day, and adds it to your account. A bank that compounds monthly divides 4.50% by 12.

The APY already includes the effect of compounding, so you do not have to do any math yourself. If a bank advertises 4.50% APY, you will earn that amount over a year if your balance stays the same — the bank has already done the compounding math and built it into the rate it shows you. This is why you can compare APY rates directly between banks without worrying about how often each one compounds.

Why different account types pay different rates

Banks offer different rates for different account types because some accounts give the bank more reliable access to your money. A regular savings account lets you withdraw money anytime, so the bank cannot count on having your deposit for long. A money market account usually requires a higher minimum balance and limits how many withdrawals you can make per month, so the bank can lend out more of that money for longer periods. A Certificate of Deposit (CD) locks your money in for a set term — three months, one year, five years — and the bank knows exactly when it can expect to have that money back.

Because the bank has more certainty with CDs and money market accounts, it pays higher rates on those accounts than on regular savings. The longer the CD term, the higher the rate usually is. Right now, a regular savings account might pay 0.01% to 0.50% APY, while a one-year CD at the same bank might pay 4.50% to 5.00% APY. The difference reflects how much more useful that locked-in money is to the bank.

When and how often interest deposits into your account

Banks compound and deposit interest on different schedules. Some compound daily but deposit interest only once a month. Others compound and deposit daily. A few still compound quarterly or semi-annually, though this is less common now. The bank's disclosure document — called the Truth in Savings Act disclosure — will tell you exactly when interest posts to your account.

You can see interest deposits in your account history. Log into your online banking, check your statement, or call the bank's customer service line. Each deposit will show as a separate transaction, often labeled "Interest Paid" or "Interest Deposit." If you do not see interest posting when you expect it, contact the bank to confirm the compounding schedule — it may be that the bank compounds daily but deposits only monthly, so you will not see anything until the deposit date arrives.

How banks calculate interest on accounts with changing balances

If you deposit money partway through a month or withdraw money, the bank recalculates your balance for each compounding period. Most banks use the daily balance method, which means they calculate interest based on your exact balance each day. If you have $5,000 on Monday and deposit $2,000 on Tuesday, the bank calculates Monday's interest on $5,000 and Tuesday's interest on $7,000.

Some banks use the average daily balance method instead, which adds up your balance for each day of the month and divides by the number of days. This method smooths out the effect of deposits and withdrawals. Either way, the bank's disclosure document will tell you which method it uses. The daily balance method usually works in your favor if you make large deposits early in the month, because your money earns interest for more days.

What happens to interest if you close your account

If you close your account before the interest deposits, you will not receive that interest. The bank stops calculating interest as soon as your account closes. If you close on the 15th of the month and the bank deposits interest on the 30th, you lose the interest that would have been paid for those 15 days. Some banks will pay accrued interest if you ask, but they are not required to — check your disclosure document or call before closing an account if you want to know the bank's policy.

If you transfer your money to another bank, make sure the receiving bank knows you want to move the account as a transfer rather than a withdrawal. A transfer keeps the account open at the original bank until the funds clear, which means you continue earning interest during the move. A withdrawal closes the account immediately and stops interest accrual.

How interest earnings affect your taxes

Interest you earn on a savings account is taxable income. You must report it on your federal tax return, and depending on your state, you may owe state income tax on it as well. If you earn $10 or more in interest during a calendar year, the bank will send you a Form 1099-INT by January 31 of the following year. You use this form to report the interest on your tax return.

If you earn less than $10, the bank does not have to send a 1099-INT, but you still owe tax on the interest. Keep your own records of interest deposits throughout the year so you can report the correct amount. The IRS matches 1099-INT forms to tax returns, so if the bank reports interest and you do not claim it, the IRS will notice.

Frequently Asked Questions

Do I earn interest on interest?

Yes, if your bank compounds interest. When the bank adds interest to your account, that interest becomes part of your balance, and the next compounding period's interest is calculated on the larger amount. This is called earning interest on interest, and it is why daily compounding earns more than monthly compounding at the same APY.

Can a bank change the interest rate on my savings account?

Yes. Banks can change rates on regular savings accounts and money market accounts anytime, usually with a few days' notice. CDs have a fixed rate for the entire term, so the rate cannot change while your money is locked in. Check your bank's website or call to see current rates.

Why is my savings account earning almost no interest?

Most traditional banks pay very low rates — often 0.01% to 0.05% APY — because they have low costs and do not need to attract deposits aggressively. Online banks and credit unions often pay higher rates because they have lower overhead and compete for deposits. If you want higher interest, compare rates at online banks and credit unions in your area.

What is the difference between APY and APR?

APY (Annual Percentage Yield) includes the effect of compounding and shows what you will actually earn. APR (Annual Percentage Rate) does not include compounding. Banks use APY for savings accounts and APR for loans. Always compare savings accounts using APY, because it reflects the real return.

Does the bank pay interest if my balance is very small?

Yes, but the amount will be very small. If you have $100 in an account earning 4.50% APY, you will earn about $4.50 per year, or roughly $0.38 per month. The bank calculates interest on whatever balance you have, no matter how small, but the payout may be less than a penny per day.