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

When you put money in a savings account, the bank lends that money to other customers as 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—usually expressed as an annual percentage rate, or APR.

The amount you earn depends on three things: how much you have in the account, what interest rate the bank offers, and how long the money sits there. A bank paying 4.5% APR on $10,000 for a full year will pay you $450 (before taxes). The same rate on $1,000 pays $45. The math is straightforward, but the timing of how banks calculate and credit that interest varies by account type and institution.

Key Takeaways

  • Interest rates on savings accounts are quoted as annual percentages (APR), but banks usually calculate and pay interest monthly or daily.
  • The difference between straightforward interest and compound interest matters: compound interest earns you interest on your interest, which accelerates growth over time.
  • Banks use either daily balance or average daily balance to calculate how much interest you owe, and the method can shift your earnings by small amounts each month.
  • Your actual earnings depend on the rate the bank offers, which changes based on Federal Reserve policy and can drop without warning.
  • Interest paid to you is taxable income and will appear on a 1099-INT form if you earn $10 or more in a calendar year.

How banks calculate interest: daily balance versus average daily balance

Most banks use one of two methods to figure out how much interest you've earned. The daily balance method calculates interest based on your account balance at the end of each day. If you have $5,000 on Monday and withdraw $1,000 on Tuesday, the bank counts $5,000 for Monday's interest and $4,000 for Tuesday's. At the end of the month, it adds up all those daily amounts and applies the interest rate.

The average daily balance method adds up your balance for each day of the month and divides by the number of days. If your balance was $5,000 for 15 days and $4,000 for 15 days, your average is $4,500. The bank applies the interest rate to that average. This method smooths out the effect of large deposits or withdrawals mid-month.

Most savings accounts use the daily balance method because it's simpler to automate. The difference between the two methods is usually small—a few cents per month on typical balances—but it matters more if you move large sums in and out frequently.

straightforward interest versus compound interest: why compounding accelerates your growth

straightforward interest means the bank pays you interest only on your original deposit. If you put in $10,000 at 4% APR and never touch it, you earn $400 the first year, $400 the second year, and so on. The interest never grows.

Compound interest means the bank pays you interest on your original deposit plus any interest you've already earned. After the first year on that same $10,000 at 4% APR, you have $10,400. In year two, the bank pays 4% on $10,400, not $10,000—earning you $416 instead of $400. That extra $16 is interest on your interest. Over decades, this difference becomes substantial.

Nearly all savings accounts use compound interest, and most compound daily or monthly. Daily compounding is slightly better than monthly because your interest starts earning interest sooner, but the difference on typical balances is small. The real driver of growth is how often the bank compounds and how high the rate is.

When banks credit interest to your account

Banks calculate interest continuously but credit it to your account on a schedule—usually monthly, sometimes quarterly. You'll see the deposit hit your account on a specific day each month, often the first or the last. Until that deposit posts, the interest is calculated but not yet yours to withdraw.

This timing matters if you're planning to move money. If you withdraw funds the day before interest posts, you lose that month's earnings. Some banks allow you to see projected interest in your account details before it actually posts, so you can plan around it.

The crediting schedule is set by the bank and doesn't change. If your account credits interest on the 1st of each month, it will always be the 1st. Check your account agreement or call the bank to confirm when yours posts.

How interest rates change and what affects them

Banks set their own savings rates, but they're influenced by the Federal Funds Rate—the interest rate the Federal Reserve charges banks to borrow from each other. When the Fed raises its rate, banks usually raise savings rates to attract deposits. When the Fed cuts rates, banks typically cut savings rates within weeks or months.

Your bank can change your rate at any time without your permission, though most will notify you in advance. Rates on savings accounts are not locked in like rates on mortgages or CDs. If your bank drops its rate from 4.5% to 3.5%, your earnings drop when ready on any new money and on future interest calculations.

This is why shopping around matters. Banks offer wildly different rates—some online banks pay 4% or higher while traditional banks pay 0.01%. Moving your money to a higher-rate account can double or triple your annual earnings on the same balance.

What happens to your interest at tax time

Interest you earn on a savings account is taxable income. If you earn $10 or more in interest during a calendar year, the bank will send you a Form 1099-INT by January 31st of the following year. You report this amount on your federal tax return.

The tax you owe depends on your overall income and tax bracket. Someone in the 22% bracket pays roughly 22 cents in federal tax for every dollar of interest earned. State income tax may explore as well, depending on where you live. This is why the real return on your savings is the interest rate minus your tax rate—a 4% account earning interest taxed at 22% nets you roughly 3.1% after taxes.

If you earn less than $10 in interest, the bank doesn't send a 1099-INT, but you still owe tax on it if you file a return. Keep your own records of interest earned in case the IRS asks.

Why some accounts earn more interest than others

High-yield savings accounts pay significantly more than traditional savings accounts at the same bank. A traditional account might pay 0.01% APR while a high-yield account at the same institution pays 4% or higher. The difference comes down to how the bank funds itself and what it does with deposits.

Online banks typically offer higher rates because they have lower overhead—no physical branches, fewer employees, lower rent. They pass those savings to customers in the form of higher rates. Traditional banks with branch networks often pay less because their costs are higher.

Money market accounts and certificates of deposit (CDs) sometimes pay more than savings accounts, but they come with restrictions. Money market accounts may limit how many withdrawals you can make per month. CDs lock your money away for a set term—three months, one year, five years—and charge a penalty if you withdraw early. The higher rate is compensation for that reduced access.

Frequently Asked Questions

Can I lose money if interest rates drop?

No. Your principal—the money you deposited—is safe. If rates drop, you straightforward earn less interest going forward. Your existing balance doesn't shrink. If you had $10,000 earning 4% and the rate drops to 2%, you still have $10,000; you just earn $200 per year instead of $400.

How much interest will I earn on $5,000 in a year?

It depends on the rate your bank offers. At 4% APR, you'd earn roughly $200 before taxes (the exact amount varies slightly based on how the bank calculates daily balances and compounds interest). At 0.5% APR, you'd earn $25. Check your bank's current rate and multiply your balance by that percentage to estimate your earnings.

Is interest credited automatically, or do I have to do something?

Interest is credited automatically on the schedule your bank sets. You don't have to do anything. The bank calculates it based on your balance and deposits it to your account on the same day each month. You can't opt out or change when it posts.

What if I withdraw money before interest is credited?

You lose the interest that would have been earned on that withdrawn amount for that period. If you withdraw $2,000 the day before interest posts, the bank calculates interest as if you never had that $2,000 that month. Once interest posts, it's yours and won't be reversed if you withdraw later.

Do I have to report interest under $10 on my taxes?

The bank doesn't send a 1099-INT for interest under $10, but you still owe tax on it if you file a return. If you file, include all interest earned, even small amounts. If you don't file a return, you're not required to report it, but keeping records is wise in case of an audit.