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 — for mortgages, car loans, credit cards, and business loans. In exchange for the use of your money, the bank pays you interest, which is a percentage of your balance. The more you have in the account and the longer it stays there, the more interest you earn.

The bank sets an interest rate, usually shown as a percentage per year. If your account earns 4% annual interest and you have $1,000 in the account for a full year with no deposits or withdrawals, you would earn $40 in interest. That $40 gets added to your account, so your new balance becomes $1,040.

Interest rates on savings accounts change. Banks raise them when the Federal Reserve raises its benchmark rate, and lower them when the Fed cuts rates. Your bank might also change your rate without the Fed moving — they compete for deposits by offering higher rates when they need more money, and lower rates when they have enough. You should check your account statement or log into your bank's website to see what rate you're currently earning.

Key Takeaways

  • Banks pay you interest on savings account balances because they lend your money to other customers and keep the difference between what they pay you and what they charge borrowers.
  • Interest rates are shown as annual percentages, but most banks calculate and add interest to your account monthly or daily.
  • The amount of interest you earn depends on three things: how much money is in the account, what rate the bank is paying, and how long the money stays there.
  • Interest rates on savings accounts change regularly based on what the Federal Reserve does and what other banks are offering.
  • Some account types, like money market accounts and certificates of deposit, often pay higher interest rates than basic savings accounts.

How banks calculate the interest you earn

Banks do not wait until the end of the year to pay you interest. Instead, they calculate interest on a daily or monthly basis and add it to your account regularly — usually monthly. This means you start earning interest on your interest, a process called compounding.

Here is a straightforward example. Say you have $1,000 in an account earning 4% annual interest, and the bank calculates interest monthly. Each month, the bank divides the annual rate by 12 (4% ÷ 12 = 0.33% per month). In month one, you earn about $3.30 on your $1,000. The bank adds that $3.30 to your account. In month two, you earn interest not just on the original $1,000, but on $1,003.30. That compounding effect is small at first, but over years it adds up.

The exact formula banks use is: Interest = Balance × (Annual Rate ÷ Number of Compounding Periods per Year) × Number of Days in the Period ÷ 365. You do not need to calculate this yourself — your bank does it automatically and shows you the interest earned on your monthly statement.

Why interest rates differ between banks and account types

Not all savings accounts pay the same interest rate. Banks that operate only online, with no physical branches, typically pay higher rates than banks with many locations. This is because online banks have lower costs — they do not pay for buildings, staff, or tellers — so they can afford to pay depositors more.

Different account types also earn different rates. A basic savings account might earn 0.01% at a large national bank, while a high-yield savings account at an online bank might earn 4% or higher. A money market account often pays more than a savings account but requires a higher minimum balance. A certificate of deposit (CD) locks your money away for a set period — three months, one year, five years — and pays a higher rate in exchange for that commitment.

The Federal Reserve's interest rate decisions affect all of these. When the Fed raises its benchmark rate, banks eventually raise what they pay on savings accounts. When the Fed cuts rates, banks lower what they pay. This is why the interest rate on your account might change from month to month, even if you do nothing.

How much interest you actually earn depends on your balance and how long money stays in the account

Two people with the same account type at the same bank might earn very different amounts of interest. The difference comes down to balance and time. A person with $10,000 earning 4% annual interest makes $400 per year. A person with $1,000 in the same account makes $40 per year. Double the balance, double the interest.

Time matters just as much. If you deposit $5,000 and withdraw it after six months, you earn interest for only half a year. If you leave $5,000 in the account for two years, you earn interest for twice as long — and because of compounding, you earn more than twice as much interest. This is why people who are saving for a goal they will not need the money for — like retirement or a house down payment years away — benefit from leaving money in savings accounts longer.

Some banks also have tiered rates, which means they pay higher interest on larger balances. For example, a bank might pay 1% on balances under $25,000 and 2% on balances of $25,000 or more. If you move from $24,999 to $25,000, your rate jumps and you start earning more interest on the entire balance.

What happens to interest when you make deposits or withdrawals

Every time you deposit money or withdraw money, your balance changes, and so does the interest you earn that day or month. Banks track your balance on each day and use the average balance over the month (or the lowest balance, depending on the bank's method) to calculate interest.

Most banks use the average daily balance method. They add up your balance at the end of each day in the month, divide by the number of days, and use that average to calculate interest. If you have $1,000 for 15 days and $2,000 for 15 days, your average balance is $1,500, and interest is calculated on $1,500.

Some banks use the lowest balance method, which is less generous to you. If your balance drops to $500 for even one day during the month, the bank calculates interest on $500 for the entire month, even if you had $5,000 for the other 29 days. Always check your account agreement to see which method your bank uses.

How interest rates affect your savings goals

The interest rate you earn matters more when you are saving larger amounts or for longer periods. If you are saving $100 per month for one year, the difference between 0.01% and 4% interest is small — maybe a few dollars. But if you are saving $500 per month for five years, that difference grows to hundreds of dollars.

This is why shopping around for a higher-rate account makes sense if you have a substantial balance. Moving $10,000 from an account earning 0.01% to one earning 4% means an extra $399 per year in your pocket. That money comes from the bank, not from your own pocket — it is real money you keep by choosing the right account.

Interest also helps protect your savings from inflation, which is the slow rise in prices over time. If inflation is 3% per year and your savings account earns 4% interest, your money is actually growing in purchasing power — you can buy more with it next year than you can today. If your account earns only 0.01% interest while inflation is 3%, your money is losing value.

Frequently Asked Questions

Do I have to pay taxes on interest I earn?

Yes. Interest earned on a savings account is taxable income. At the end of each year, your bank sends you a Form 1099-INT showing how much interest you earned. You report this on your tax return. The amount of tax you owe depends on your total income and tax bracket. If you earned only $10 in interest, the tax impact is small. If you earned $1,000, it is more significant.

Can my interest rate go down after I open the account?

Yes. Banks can lower the interest rate on your account at any time, though they usually give you notice first. Your rate can also go up if the bank decides to offer higher rates to attract deposits. You can move your money to a different bank if your rate drops and you find a better offer elsewhere.

What is the difference between APY and APR?

APY stands for Annual Percentage Yield and includes the effect of compounding — it shows the real amount you will earn in a year. APR stands for Annual Percentage Rate and does not include compounding. Banks must show you the APY on savings accounts, so that is the number to compare when shopping for accounts.

Does interest get added to my account automatically?

Yes. Banks calculate interest and add it to your balance automatically, usually once per month. You do not have to do anything. You will see the interest posted on your statement and in your account balance.

What if I withdraw money before the end of the month?

You still earn interest on the money you had in the account, calculated based on how many days it was there. If you deposit $1,000 on the first of the month and withdraw it on the 15th, you earn interest for 15 days. The bank calculates this automatically — you do not lose all interest just because you withdrew before month-end.