Your bank pays you interest on the money you deposit

When you put money in a savings account, the bank uses that money to lend to other customers or invest it. In return, the bank pays you interest—a percentage of your balance, calculated and added to your account on a schedule the bank sets. That interest is how your money increases without you depositing more.

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 calculates and adds the interest to your balance. A higher rate means more money added each period. A larger balance means the interest is calculated on a bigger number. More frequent compounding means you earn interest on your interest sooner.

The interest rate varies by bank and by the type of account. A regular savings account at a large national bank might offer 0.01% annual interest. A high-yield savings account at an online bank might offer 4.5% or higher. The difference between those two rates means thousands of dollars over time on the same deposit.

Key Takeaways

  • Banks pay interest on your savings balance as a percentage per year, and that interest is added to your account on a schedule set by the bank.
  • The interest rate varies widely by bank and account type—online banks and high-yield accounts typically pay more than traditional bank savings accounts.
  • Interest compounds when the bank adds earned interest back to your balance, so you then earn interest on that interest in the next period.
  • You can compare rates across banks before opening an account, and rates can change after you open one, so checking periodically matters.

How the bank calculates and adds interest to your account

Banks calculate interest using a formula based on your balance, the annual interest rate, and the time period. Most savings accounts use daily compounding, meaning the bank divides the annual rate by 365, applies that daily rate to your balance each day, and adds the result to your account. At the end of the month or quarter, you see the total interest earned during that period posted to your balance.

For example: if your account has $10,000 and the annual rate is 4.5%, the bank calculates roughly $1.23 in interest per day (4.5% ÷ 365 = 0.0123% per day; $10,000 × 0.0123% = $1.23). Over 30 days, that adds up to about $36.90 in interest, which the bank adds to your account. Your new balance becomes $10,036.90, and in the next period, interest is calculated on that higher amount.

The schedule for posting interest varies. Some banks add it monthly, others quarterly. Check your account agreement or the bank's website to see when interest posts. The more frequently interest is added, the sooner you earn interest on that interest—a process called compounding.

The difference between APY and the interest rate

Banks advertise two numbers: the interest rate and the APY (annual percentage yield). The interest rate is the percentage the bank pays. The APY is what you actually earn over a year when compounding is included.

If a bank offers 4.5% interest with daily compounding, the APY will be slightly higher—perhaps 4.60%—because you earn interest on your interest throughout the year. The difference grows larger with higher rates and more frequent compounding. When comparing accounts, use the APY number, not the interest rate, because APY shows what you will actually receive.

Banks are required to display APY prominently on their website and in account disclosures, so you can compare across institutions without doing the math yourself.

Why interest rates change and how to monitor yours

Banks set their own interest rates based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, banks typically raise the rates they offer on savings accounts. When the Fed lowers rates, banks lower theirs. This can happen multiple times per year, or not at all for months.

Your rate can change after you open the account. Banks are required to notify you before lowering your rate, usually by email or mail, and you have the right to close the account without penalty if you disagree. If rates rise, the bank may or may not raise your rate—some do automatically, others do not. This is why checking your account's current APY every few months matters, especially if you have been with the same bank for a long time.

Online banks and high-yield savings accounts tend to adjust rates more quickly and more often than traditional banks, because they compete directly on rate and have lower overhead costs. If your bank's rate falls significantly below what others offer, moving your money to a higher-paying account can add hundreds or thousands of dollars per year.

How much your money will grow over time

The longer your money sits in the account, the more interest accumulates. With daily compounding, the growth accelerates because each day's interest is added to the balance, and the next day's interest is calculated on that larger amount.

Here is a concrete example: $10,000 deposited in an account paying 4.5% APY with daily compounding will grow to approximately $10,460 after one year, $10,942 after two years, and $11,449 after three years—all without you adding a single dollar. The difference between year one and year two is $482 in interest earned. The difference between year two and year three is $507 in interest earned. That acceleration is compounding at work.

The same $10,000 in an account paying 0.01% APY would grow to only $10,001 after one year. Over three years, you would earn just $3 in total interest. The choice of account matters enormously.

What reduces or stops your interest from growing

Interest stops accruing the moment you withdraw money. If you withdraw $5,000 from a $10,000 balance, the next interest calculation is based on the remaining $5,000, not the original amount. Some banks also charge monthly maintenance fees that reduce your balance and therefore reduce the interest you earn.

Certain savings accounts have restrictions on how many times per month you can withdraw without penalty. Checking your account agreement for withdrawal limits and fees is important, because frequent withdrawals or high fees can eat into your interest earnings.

Inflation also reduces what your interest earnings are worth in real terms. If your account earns 4.5% but inflation is 3%, your money is only growing in purchasing power by about 1.5%. This is why comparing rates across banks and choosing the highest available rate matters—it helps you stay ahead of inflation.

Frequently Asked Questions

Can I lose money in a savings account?

No. Your balance cannot go down due to interest calculations or market changes. Interest only adds to your balance. You can only lose money by withdrawing it yourself or if the bank charges fees that exceed your interest earnings, which is rare in modern accounts.

Is the interest I earn taxable?

Yes. Interest earned in a savings account is considered income by the IRS and must be reported on your tax return. Banks send you a 1099-INT form each January if you earned $10 or more in interest during the previous year. The interest is taxed at your ordinary income tax rate, not at a special rate.

What happens to my interest if I close the account?

You keep all interest earned up to the day you close the account. The bank calculates interest through your closing date and adds it to your final balance before you withdraw the money. No interest accrues after the account is closed.

Does moving my money between accounts affect how much interest I earn?

No. Interest is calculated daily on whatever balance sits in the account on that day. If you transfer money out, interest stops accruing on that amount when ready. If you transfer money in, interest begins accruing on the new amount the next day. The total interest you earn depends on how much money was in the account and for how long.

Why do some banks offer much higher rates than others?

Online banks have lower operating costs than physical branches, so they can afford to pay higher rates and still make a profit. They compete directly on rate because they cannot compete on convenience or personal service. Traditional banks with many branches have higher costs and often pay lower rates. Both are safe as long as they are FDIC-insured, which protects your deposits up to $250,000.