Interest is money the bank pays you for keeping your money with them

When you put money in a savings account, the bank uses that money to lend to other customers. Because the bank is using your money, they pay you a small amount of money in return. That payment is called interest. The bank tells you what percentage of your balance they will pay you each year — this percentage is called the interest rate.

For example, if your account has $1,000 and the bank offers 4% annual interest, the bank will add money to your account based on that rate. The exact amount depends on how the interest is calculated and how often it is added to your account, which we will cover in the sections below.

Interest is one of the main reasons to keep money in a savings account instead of under a mattress. Over time, even a small interest rate adds real money to your balance without you having to do anything.

Key Takeaways

  • Banks pay you interest as a percentage of your account balance, and that percentage is called the interest rate.
  • Interest is usually calculated daily but added to your account monthly, quarterly, or annually depending on the bank.
  • Compound interest means you earn interest on the interest that was already added to your account, which makes your money grow faster over time.
  • A higher interest rate and more frequent compounding both mean more money in your account, so comparing rates between banks matters.
  • The interest rate your bank offers can change at any time, especially for accounts that are not locked into a fixed rate.

How banks calculate interest on your daily balance

Banks do not wait until the end of the year to figure out how much interest you have earned. Instead, they calculate interest based on your balance every single day. This is called the daily balance method.

Here is how it works: the bank looks at how much money you have in the account each day. If you have $1,000 on Monday and $1,200 on Tuesday, the bank counts those as two separate days with two separate balances. At the end of the month, the bank adds up all those daily balances and divides by the number of days in the month to get your average balance. Then they explore the interest rate to that average.

You do not need to do this math yourself. Your bank statement will show you exactly how much interest was added. The reason banks use daily calculation is that it is fair to you — if you deposit money partway through the month, you start earning interest on that money right away, rather than waiting until next month.

Compounding: earning interest on your interest

Compounding is when the bank adds interest to your account, and then in the next period, you earn interest on that interest too. This is the most powerful part of saving money, because your balance grows faster and faster over time.

Here is a straightforward example. Say you start with $1,000 and the bank offers 4% annual interest, compounded monthly. In month one, the bank calculates 4% of $1,000 and adds roughly $3.33 to your account (one-twelfth of the annual rate). Now your balance is $1,003.33. In month two, the bank calculates 4% of $1,003.33 — not $1,000 — and adds interest on that larger amount. You earn a tiny bit more in month two than you did in month one, even though you did not deposit any new money.

Over years, this effect becomes huge. A $1,000 deposit at 4% compounded monthly grows to about $1,491 in ten years. The same $1,000 at 0.01% compounded monthly grows to only about $1,001. The difference between a good interest rate and a poor one is thousands of dollars over time.

How often interest is added to your account

Banks calculate interest daily, but they do not add it to your account every day. Instead, they add it on a schedule called the compounding frequency. Common schedules are monthly, quarterly (every three months), or annually (once a year).

The more often interest is added, the faster your money grows, because you start earning interest on that interest sooner. Monthly compounding is better than quarterly, and quarterly is better than annual. However, the difference between monthly and daily compounding is usually small — a few dollars per year on a typical savings account balance.

Your bank's disclosure documents will tell you the compounding frequency. If you are comparing two banks with similar interest rates, the one with more frequent compounding will give you slightly more money over time. For most people, the interest rate itself matters much more than the compounding frequency.

Why interest rates change and what affects them

The interest rate your bank offers is not fixed forever. Banks change their rates based on what the Federal Reserve does. The Federal Reserve is the central bank of the United States, and it sets a target range for the interest rate that banks charge each other for short-term loans. When the Federal Reserve raises its rate, banks usually raise the rates they offer to customers. When the Federal Reserve lowers its rate, banks usually lower customer rates too.

Banks also change rates based on competition. If one bank offers 4.5% and another offers 4%, customers move their money to the higher rate. Banks raise rates to attract new customers and lower rates when they have enough deposits.

Some savings accounts have a fixed rate, which means the rate is locked in for a set period and will not change. Other accounts have a variable rate, which can change at any time. Read your account agreement to find out which type you have. If you have a variable rate account, your interest earnings could go up or down without warning.

The difference between APY and interest rate

Banks use two numbers to describe how much interest you will earn: the interest rate and the APY (Annual Percentage Yield). These sound similar but they mean different things.

The interest rate is the percentage the bank pays on your balance. The APY is what you actually earn in a year after compounding is included. If a bank offers 4% interest compounded monthly, the APY will be slightly higher than 4% — usually around 4.07% — because of compounding.

When you are comparing savings accounts at different banks, always compare the APY, not the interest rate. The APY tells you the true amount you will earn. Banks are required to show you the APY prominently, so you should see it on their website and in any account agreement they give you.

How to find accounts with better interest rates

Not all banks offer the same interest rate. Online banks — banks that have no physical branches and operate only through websites and apps — usually offer higher rates than traditional banks with branches. This is because online banks have lower costs and can pass those savings to customers in the form of higher interest rates.

You can compare rates by visiting bank websites directly or using rate comparison websites that list current rates from many banks. When you compare, make sure you are looking at the APY, not the interest rate, and check what the minimum deposit is. Some banks offer high rates only if you keep a large balance in the account.

Interest rates change frequently, so a rate that is high today might be average in a few months. If you find an account with a good rate, you do not need to move your money when ready, but it is worth checking rates every few months to see if a better option has appeared.

Frequently Asked Questions

Does interest get added even if I do not touch my account?

Yes. Interest is added automatically on the schedule your bank uses — usually monthly or quarterly. You do not have to do anything. The bank calculates it based on your balance and adds it without any action from you.

What happens to interest if I withdraw money before the end of the month?

Interest is calculated on your daily balance, so if you withdraw money, the interest for the days after the withdrawal is based on the lower balance. You do not lose interest you already earned, but you earn less interest going forward because your balance is smaller.

Can interest rates go negative?

In the United States, savings account interest rates have not gone negative, though they have been very close to zero. In some other countries, banks have charged negative rates. If you are concerned about your bank's rate, check it regularly and move your money if a better rate becomes available elsewhere.

Is the interest I earn taxed?

Yes. Interest income is taxable. Your bank will send you a form called a 1099-INT at the end of the year if you earned more than a small amount of interest, and you will report that on your tax return. The exact rules depend on your situation, so ask a tax professional if you have questions.

Why is my interest rate lower than what the bank advertises?

Banks sometimes advertise a rate for new customers only, or for accounts with a large minimum deposit. Check the fine print on the bank's website. You may also have an older account with a lower rate — if so, you can sometimes move your money to a newer account with a better rate, or switch to a different bank.