Interest is money the bank pays you for letting them use your money

When you deposit money into a savings account, the bank lends that money to other customers through mortgages, car loans, and business lines of credit. The bank keeps the difference between what it pays you and what it charges borrowers. That payment to you is interest—a percentage of your account balance that the bank adds to your account on a set schedule, usually monthly or daily.

The amount you earn depends on three things: how much money you have in the account, the interest rate the bank offers, and how often the bank compounds that interest. A bank might advertise a 4.5% annual percentage yield (APY), but that does not mean you earn 4.5% of your balance once a year. The actual mechanics are more specific, and understanding them helps you compare accounts and predict what you will actually receive.

Key Takeaways

  • Interest is calculated as a percentage of your account balance, and the rate varies by bank and account type—there is no single rate all banks use.
  • APY (annual percentage yield) is the rate you will actually earn in a year when compounding is included, while APR (annual percentage rate) does not account for compounding.
  • Compounding means the bank adds interest to your balance, then calculates next month's interest on the new, larger balance—this is why the frequency matters.
  • You only earn interest on money that stays in the account; withdrawals reduce your balance and the interest you earn that period.
  • High-yield savings accounts at online banks typically pay 4% to 5% APY, while traditional brick-and-mortar banks often pay under 0.5% APY on the same deposit.

How the bank calculates your interest each period

Banks calculate interest using a straightforward formula: your account balance multiplied by the interest rate, divided by the number of times per year interest is compounded. If you have $10,000 in an account with a 4.8% APY and the bank compounds interest monthly, the calculation for one month looks like this: $10,000 × (0.048 ÷ 12) = $40. That $40 is added to your account at the end of the month.

The key phrase is "at the end of the month." Most banks calculate interest daily but deposit it monthly. This means the bank is tracking your balance every single day, but you do not see the money appear in your account until the compounding date arrives. Some banks compound daily, some weekly, some monthly. The more frequently a bank compounds, the more interest you earn, because you earn interest on your interest sooner.

If your balance changes during the month—say you deposit $5,000 on the 15th—the bank recalculates. Your interest for the first 14 days is based on $10,000, and your interest for the remaining days is based on $15,000. The total interest for the month reflects both balances. Withdrawals work the same way: the day you withdraw, your balance drops, and interest for the rest of the month is calculated on the lower amount.

Why APY matters more than the advertised rate

Banks are required to disclose the APY, not just the interest rate, because APY tells you what you will actually earn. The difference between the two comes down to compounding. If a bank offers 4.8% compounded monthly, the actual annual yield is slightly higher than 4.8% because you earn interest on your interest. The bank calculates this and publishes it as the APY—in this case, around 4.91%.

When you see a savings account advertised at "4.8% APY," that 4.8% already includes the effect of compounding. You do not need to do any math; that is what you will earn over a year if your balance stays the same and you make no deposits or withdrawals. If you compare two accounts, always compare the APY figures, not the base rates. A 4.5% APY compounded daily will earn you more than a 4.6% APY compounded monthly.

What happens to your interest if you withdraw money

Interest is calculated on the balance you hold, so withdrawals reduce what you earn. If you have $20,000 on the first of the month and withdraw $5,000 on the 20th, you earn interest on $20,000 for 19 days and on $15,000 for 11 days. The bank prorates your interest across both balances. Over a full year, frequent withdrawals can noticeably reduce your earnings compared to keeping the money untouched.

Some savings accounts have withdrawal limits or penalties if you exceed them. Federal Regulation D historically limited savings account withdrawals to six per month, though that rule was suspended in 2020 and has not been reinstated. Individual banks may still impose their own limits or charge fees for excess withdrawals. Check your account terms before opening, because a penalty could wipe out several months of interest.

The difference between high-yield and traditional savings accounts

A high-yield savings account is straightforward a savings account where the bank offers a much higher interest rate than a traditional account. Online banks typically offer 4% to 5% APY because they have lower overhead costs—no physical branches, fewer employees, lower rent. Traditional banks with branch networks often pay under 0.5% APY on the same deposit. The account type is identical; the only difference is the rate.

Your money is equally safe in either account. Both are insured by the Federal Deposit Insurance Corporation (FDIC) up to $250,000 per depositor per bank. The trade-off is convenience: a high-yield account at an online bank means no in-person deposits or withdrawals, though most allow transfers to and from external accounts. If you rarely need to access your savings, a high-yield account can earn you hundreds of dollars per year more than a traditional account.

How interest rates change and what that means for your earnings

Banks set their own interest rates and can change them at any time. When the Federal Reserve raises or lowers its benchmark interest rate, banks typically adjust their savings rates within days or weeks. If rates rise, your earnings increase. If rates fall, your earnings decrease. You do not have to do anything; the new rate applies automatically to your account.

Interest rates have varied dramatically over the past decade. In 2020 and 2021, savings rates were near zero. By late 2023, high-yield accounts reached 5% APY. By mid-2024, rates had fallen back to 4% to 4.5%. These swings mean the amount you earn can change significantly from year to year, even if your balance stays the same. There is no way to lock in a rate on a savings account; the rate is variable unless you move your money to a certificate of deposit (CD), which offers a fixed rate for a set term.

How to predict what you will earn

To estimate your annual interest, multiply your account balance by the APY and divide by 100. If you have $25,000 in an account with a 4.5% APY, your annual interest is approximately $1,125 (before any fees). If you add $500 per month, the calculation becomes more complex, but most banks show a projected interest figure in your online account dashboard.

Keep in mind this is an estimate. The actual amount depends on your exact balance each day, any fees the bank charges, and whether the interest rate changes during the year. If you withdraw money mid-year or the bank lowers its rate, your earnings will be lower. If you deposit money or the bank raises its rate, your earnings will be higher. The dashboard projection updates as your balance and the rate change, so check it periodically to see how your savings are growing.

Frequently Asked Questions

Do I have to pay taxes on the interest I earn?

Yes. Interest income is taxable as ordinary income. The bank will send you a Form 1099-INT at the end of the year showing how much interest you earned, and you report that on your tax return. The amount is usually small unless you have a large balance or a high interest rate, but it still counts as income.

What is the difference between APY and APR?

APY includes the effect of compounding, while APR does not. For savings accounts, always look at the APY because that is what you will actually earn. APR is more commonly used for loans and credit cards, where it works the opposite way—higher APR costs you more money.

Can I move my money to a different bank if the interest rate drops?

Yes. You can withdraw your money and deposit it at another bank at any time. There is no penalty for moving your savings. If your current bank lowers its rate and another bank offers a higher rate, moving your money makes financial sense. Just make sure the new bank is FDIC-insured and that you understand any minimum balance requirements.

Does the order of my deposits and withdrawals affect how much interest I earn?

The bank calculates interest based on your daily balance, so the timing of deposits and withdrawals matters. Money deposited early in the month earns interest for more days than money deposited late in the month. Similarly, withdrawing money early in the month means you earn less interest that month than if you withdraw late. The difference is usually small unless the amounts are large.

What happens to my interest if the bank goes out of business?

Your deposits up to $250,000 are protected by FDIC insurance, which means you get your money back even if the bank fails. The interest you earned up to the point of failure is also covered. You will not earn interest after the bank closes, but your principal and accrued interest are safe.