Banks pay interest by calculating a percentage of your balance and crediting that amount to your account on a set schedule—usually monthly or daily, depending on the account type and the bank's terms.
The amount you earn depends on three things: how much money sits in the account, what annual percentage yield (APY) the bank offers, and how often the bank compounds the interest—meaning how often it calculates interest on your interest. A bank that compounds daily will pay you slightly more than one that compounds monthly, even at the same stated rate.
You don't have to do anything to receive the interest. Once you open the account and deposit money, the bank's system automatically calculates what you've earned and adds it to your balance. The interest becomes part of your account and earns interest itself the next time the bank compounds.
Key Takeaways
- Interest is calculated as a percentage of your balance and paid on a schedule set by your bank, usually monthly or daily.
- The annual percentage yield (APY) tells you the real rate you'll earn in a year, including the effect of compounding.
- Compounding frequency matters: daily compounding pays slightly more than monthly compounding at the same APY.
- Interest rates on savings accounts change over time and vary widely between banks, so comparing rates before opening an account makes a real difference.
What APY means and how it differs from interest rate
Banks advertise two different numbers: the interest rate and the annual percentage yield (APY). The interest rate is the percentage the bank applies to your balance. The APY is what you actually earn in a year when compounding is included.
If a bank offers 4.5% APY on a savings account, that means if you leave $1,000 in the account for a full year without touching it, you'll have roughly $1,045 at the end—assuming the rate doesn't change. The difference between the interest rate and the APY is usually small, but it's real money. A bank that compounds daily at the same stated rate will show a slightly higher APY than one that compounds monthly.
The APY is what you should compare when looking at different banks. It's the number that tells you what you'll actually earn. The interest rate alone doesn't account for compounding and can be misleading.
How compounding works and why frequency matters
Compounding means the bank calculates interest on your original balance plus any interest you've already earned. Each time the bank compounds, it adds the new interest to your account, and the next calculation includes that amount.
Here's a concrete example: if you have $10,000 at 4% APY compounded daily, the bank divides the annual rate by 365 and calculates interest each day. On day one, you earn roughly $1.10. On day two, you earn interest on $10,001.10, not just the original $10,000. Over a year, this daily compounding adds up to more than if the bank compounded monthly.
The difference between daily and monthly compounding at the same APY is usually between $5 and $15 per $10,000 per year—not huge, but real. The more frequently a bank compounds, the more you earn. Most online banks compound daily. Some traditional banks compound monthly or quarterly. Your account statement or the bank's disclosure documents will tell you the compounding frequency.
When interest is credited to your account
Banks credit interest on different schedules. Some add it monthly on the same date each month. Others add it daily but show the total once a month on your statement. A few add it quarterly. The schedule doesn't change how much you earn in a year—the APY accounts for the frequency—but it does affect when you see the money in your account.
Most banks show the interest earned in your account within one to three business days of the end of the month. Some online banks credit it the same day. You can usually see the exact date in your account agreement or by calling the bank's customer service line.
Once interest is credited, it becomes part of your balance and earns interest itself. This is why compounding matters over time: your money grows faster because you're earning returns on returns.
Why interest rates change and how that affects you
Savings account interest rates are not fixed. Banks raise and lower them based on what the Federal Reserve does with its benchmark interest rate. When the Fed raises rates, banks typically raise savings rates within days or weeks. When the Fed cuts rates, banks cut savings rates more slowly, but they do cut them.
If you lock in a high rate today, that rate is not may provide forever. Your bank can lower it at any time, though they must notify you in writing before the change takes effect. Some banks lower rates after a few months; others keep them stable for longer. There's no rule about how long a rate lasts.
This is why the rate you see advertised when you open an account might not be the rate you earn a year from now. It's also why comparing rates across banks matters: a bank offering 4.5% today might drop to 3.5% in six months, while another bank keeps a competitive rate longer. You can move your money to a different bank if your current rate drops too far, though you'll want to check whether there are any early withdrawal penalties in your account agreement.
How to calculate what you'll earn
You can estimate your earnings using the APY and your balance. The straightforward formula is: balance × APY = annual interest earned. If you have $5,000 at 4.5% APY, you'll earn roughly $225 in a year.
This is an estimate because the actual amount depends on whether your balance stays the same all year. If you add money during the year, you'll earn more. If you withdraw money, you'll earn less. The bank calculates interest on your actual balance each day, so deposits and withdrawals change what you earn.
Most banks provide an interest calculator on their website where you can enter your balance and see a projection. Your monthly statement also shows how much interest you've earned so far that month and year to date. These numbers let you track whether the rate you're getting matches what the bank promised.
What happens if you withdraw money before interest is credited
If you withdraw money before the bank credits interest for the month, you lose the interest on that amount. For example, if you have $10,000 on the first of the month and withdraw $5,000 on the 15th, the bank calculates interest on the full $10,000 for the first 15 days and on $5,000 for the remaining days. You don't lose interest you've already earned, but you don't earn interest on money that's no longer in the account.
This is why the timing of deposits and withdrawals matters if you're trying to maximize earnings. Leaving money in the account longer means more interest. Most savings accounts have no penalty for withdrawals, but some accounts—like certain promotional accounts—may have restrictions. Check your account agreement to see whether there are any limits on how often you can withdraw.
Frequently Asked Questions
Is the interest I earn on a savings account taxable?
Yes. Interest earned on a savings account is taxable income. Banks send you a 1099-INT form at the end of the year if you earned $10 or more in interest. You report this on your tax return. The amount you owe in taxes depends on your tax bracket and total income.
Can a bank change my interest rate without telling me?
No. Banks must notify you in writing before lowering your rate. The notification usually comes by mail or email and includes the new rate and the date it takes effect. You have the right to close the account before the new rate applies if you disagree with the change.
Why do online banks pay higher interest than traditional banks?
Online banks have lower overhead costs because they don't operate physical branches. They pass some of those savings to customers through higher interest rates. Traditional banks with many branches have higher operating costs and often pay lower rates on savings accounts.
What's the difference between a savings account and a money market account in terms of interest?
Both earn interest, but money market accounts typically offer slightly higher rates in exchange for requiring a larger minimum balance and limiting how often you can withdraw. The interest calculation works the same way—APY, compounding, and monthly crediting. Check the rates at your bank to see which account pays more for your situation.
Does moving money between accounts affect how much interest I earn?
No. Interest is calculated on your balance each day. If you move money from one account to another at the same bank, you earn interest on whichever account holds the money on any given day. Moving money between different banks doesn't affect the interest calculation, though it may take a few days for the transfer to complete.