Banks pay you interest as a percentage of the money you keep in an account, calculated daily or monthly and added to your balance over time.

When you deposit money into a savings account, the bank uses that money to lend to other customers or invest it. In return, the bank pays you a small percentage of your balance as interest. The amount you earn depends on three things: how much money sits in the account, what interest rate the bank offers, and how often the bank compounds the interest—meaning how often it adds earned interest back into your account so you earn interest on that interest too.

The interest rate varies widely. A high-yield savings account at an online bank might offer 4% to 5% annually, while a traditional brick-and-mortar bank savings account might offer 0.01% to 0.5%. The difference between these rates is real money: on $10,000, the difference between 0.01% and 4.5% is roughly $450 per year. Banks set their rates based on what the Federal Reserve charges them to borrow money, competition from other banks, and how much they need deposits at any given time.

Key Takeaways

  • Interest is calculated as a percentage of your account balance, and the rate varies by bank and account type—online banks typically offer higher rates than traditional banks.
  • Compounding means the bank adds earned interest back into your account, so you earn interest on your interest, which accelerates growth over time.
  • The frequency of compounding (daily, monthly, or annually) affects how much total interest you receive, with daily compounding producing slightly more than monthly or annual.
  • Your interest earnings are reported to the IRS on a Form 1099-INT if you earn $10 or more in a year, and you owe income tax on that amount.

How the Interest Rate Gets Applied to Your Balance

Banks calculate interest using a formula based on your principal (the money you deposited), the annual interest rate, and the time period. For a savings account, the calculation usually looks like this: Interest = Principal × Annual Rate ÷ 365 × Number of Days. If you have $5,000 in an account earning 4% annually, the bank divides 4% by 365 days, then multiplies that daily rate by your balance each day, then adds up all those daily amounts at the end of the month or quarter.

This means your balance matters every single day. If you deposit $5,000 on the first of the month and withdraw $4,000 on the fifteenth, the bank calculates interest on $5,000 for 14 days and $1,000 for the remaining days. Some banks use the "average daily balance" method instead, which adds up your balance at the end of each day and divides by the number of days in the period—this smooths out the effect of deposits and withdrawals.

What Compounding Does and Why It Matters

Compounding is when the bank adds interest you've earned back into your account, so the next interest calculation includes that earned interest. If you earn $10 in interest one month, the next month's interest is calculated on your original balance plus that $10. Over years, this creates a snowball effect where your money grows faster than it would with straightforward interest alone.

The frequency of compounding affects your total earnings. Daily compounding (the most common for savings accounts) produces slightly more than monthly compounding, which produces slightly more than annual compounding. The difference is small on modest balances—on $10,000 at 4% annually, daily compounding earns roughly $408 per year while annual compounding earns $400—but it widens as your balance grows or you keep money in the account longer.

Banks must disclose their compounding frequency in the account terms, usually found on their website or in the account agreement. Look for language like "compounded daily" or "compounded monthly and credited monthly." The word "credited" means the interest is actually added to your account; some banks calculate interest daily but credit it only monthly, which is still daily compounding.

Why Interest Rates Change and How to Compare Them

Banks adjust their interest rates in response to changes in the Federal Reserve's benchmark rate, which is the rate the Fed charges banks to borrow from each other. When the Fed raises its rate, banks typically raise the rates they offer on savings accounts within weeks or months. When the Fed cuts its rate, banks usually cut savings rates too, though sometimes more slowly. This means the rate you see today may not be the rate you earn six months from now.

To compare rates across banks, look at the Annual Percentage Yield (APY), not just the interest rate. APY includes the effect of compounding, so it shows you the actual percentage of your balance you'll earn in a year. A bank advertising "4% APY" will earn you more than one advertising "4% interest rate compounded annually" because the APY figure already accounts for compounding.

Online banks and credit unions typically offer higher rates than traditional banks because they have lower overhead costs and compete aggressively for deposits. However, the highest rate is only useful if the bank is FDIC-insured (for banks) or NCUA-insured (for credit unions), which protects your deposits up to $250,000 if the institution fails. All legitimate banks and credit unions carry this insurance; verify it on the FDIC or NCUA website before moving money.

How Interest Earnings Affect Your Taxes

Interest you earn on a savings account is taxable income. If you earn $10 or more in interest during a calendar year, the bank sends you a Form 1099-INT by January 31 of the following year, and they also send a copy to the IRS. You report this amount on your tax return as ordinary income, and you owe federal income tax on it at your regular tax rate.

Some states also tax interest income, though a few states exempt interest from state income tax. Check your state's tax rules or ask a tax professional if you're unsure. The tax liability exists whether the bank sends you a 1099-INT or not—you're responsible for reporting all interest earned, even if the amount is under $10.

The Difference Between Savings Accounts, Money Market Accounts, and Certificates of Deposit

Different account types earn interest at different rates and with different rules. A savings account has no minimum balance requirement at most banks, allows unlimited deposits and withdrawals (though federal rules once limited withdrawals to six per month—this limit is no longer enforced, but some banks still have their own limits), and earns interest daily or monthly. A money market account is a hybrid: it earns a higher interest rate than a savings account but usually requires a higher minimum balance (often $2,500 to $10,000) and may limit withdrawals.

A Certificate of Deposit (CD) locks your money away for a fixed period—typically three months to five years—in exchange for a higher interest rate. If you withdraw before the term ends, you pay a penalty, usually equal to a few months of interest. CDs are useful if you know you won't need the money and want to lock in a rate before rates fall, but they're not flexible.

High-yield savings accounts are savings accounts with higher interest rates, usually offered by online banks. They work the same way as traditional savings accounts—no lock-in period, no minimum balance, daily compounding—but the rate is often two to five times higher because the bank has lower costs.

What Happens When Interest Rates Fall

When the Federal Reserve cuts its benchmark rate, banks lower the rates they offer on savings accounts. This can happen quickly—sometimes within days of a Fed announcement. If you're earning 4.5% on a savings account and rates drop to 3%, your rate will likely drop too within a few weeks. Your existing balance doesn't disappear, but the interest you earn on future deposits and balances will be lower.

This is why some people move money to CDs when rates are high: they lock in the current rate for a set period, protecting themselves against future rate cuts. However, if rates rise instead, you're stuck with the lower CD rate while new savings accounts earn more. There's no perfect strategy—it depends on whether you think rates will rise or fall, which nobody can predict with certainty.

Frequently Asked Questions

How often does the bank add interest to my account?

Interest is calculated daily at most banks, but it's credited (actually added to your account) monthly, quarterly, or annually depending on the bank. Check your account agreement or the bank's website for the crediting schedule. Daily calculation with monthly crediting is standard for savings accounts.

Can I lose money if interest rates fall?

No. Your principal—the money you deposited—is never at risk from interest rate changes. You straightforward earn less interest going forward. If rates fall from 4% to 2%, you still have all your original money; you just earn interest at the new, lower rate.

What's the difference between APR and APY?

APR (Annual Percentage Rate) is the interest rate without compounding. APY (Annual Percentage Yield) includes the effect of compounding. For savings accounts, always compare APY, not APR, because APY shows what you'll actually earn in a year.

Do I owe taxes on interest I haven't withdrawn yet?

Yes. You owe income tax on interest earned in the year it's credited to your account, whether you withdraw it or leave it there. The bank reports this on Form 1099-INT, and you report it on your tax return.

Is my interest may provide if I open a savings account today?

No. The rate you see today can change at any time, and banks typically lower rates when the Federal Reserve cuts its benchmark rate. The only way to lock in a rate is to open a CD, which guarantees the rate for the term you choose.