Interest grows your savings through daily calculation and regular deposits
Banks pay you interest on the money you keep in a savings account. The amount you earn depends on three things: how much money sits in the account, the annual percentage yield (APY) the bank offers, and how often the bank compounds the interest—meaning how often it calculates interest on your interest.
Most banks compound interest daily, which means they calculate what you owe every single day and add those tiny amounts together. Some compound monthly or quarterly instead. The more often compounding happens, the more interest you earn, because you start earning interest on yesterday's interest right away.
The bank pays you this interest either monthly, quarterly, or annually, depending on the account. You'll see the deposit hit your account on a regular schedule—usually the last day of the month or the first day of the next month. The interest becomes part of your account balance immediately, so it starts earning interest itself the next compounding cycle.
Key Takeaways
- Banks calculate interest daily by multiplying your account balance by the APY and dividing by 365, then add that amount to your balance each day.
- Compounding means interest earns interest: the daily interest gets added to your balance, and tomorrow's calculation includes today's interest.
- The bank deposits your earned interest into your account on a schedule (usually monthly), and that money immediately starts earning interest too.
- A higher APY and a larger balance both increase how much interest you earn, but compounding frequency matters most when balances are large.
- Interest earned on savings accounts is taxable income and will appear on a 1099-INT form if you earn more than $10 in a year.
The daily calculation: how much interest you earn each day
Banks use a simple formula to calculate daily interest. They take your account balance, multiply it by the APY, and divide by 365 (the number of days in a year). That gives them the interest you earn for one day.
Example: if your balance is $5,000 and the APY is 4.5%, the bank calculates $5,000 × 0.045 ÷ 365 = $0.62 per day. That $0.62 gets added to your balance at the end of the day (or sometimes at the end of the month, depending on the bank's schedule). Tomorrow, if your balance is still $5,000, you earn another $0.62. If you deposited $1,000 more, tomorrow's calculation uses $6,000, so you earn $0.74 instead.
The bank does this calculation every single day your account is open. You don't see these tiny daily additions—they're invisible until the bank officially deposits your interest into your account. But they're happening, and they're adding up.
How compounding turns small daily interest into larger amounts
Compounding is the process of earning interest on interest. On day one, the bank calculates interest on your original balance. On day two, it calculates interest on your original balance plus yesterday's interest. On day three, it calculates interest on everything that's now in the account—the original balance, plus two days of interest.
This creates a snowball effect. The more days that pass, the larger your balance grows, and the larger the daily interest calculation becomes. A $5,000 balance earning $0.62 per day grows to $5,000.62. The next day's calculation is based on $5,000.62, not $5,000, so you earn slightly more than $0.62.
Over a year, this difference is real. On a $5,000 balance at 4.5% APY with daily compounding, you earn about $230 in interest. With monthly compounding instead, you'd earn about $229. The difference is small on smaller balances, but on $50,000 at the same rate, daily compounding earns you about $2,305 versus $2,294 with monthly compounding—an extra $11 per year just from compounding more often.
When the bank deposits your interest into your account
The bank doesn't add interest to your balance every single day. Instead, it lets the daily calculations accumulate, then deposits the total interest into your account on a set schedule. Most banks deposit interest monthly—usually on the last day of the month or the first day of the next month. Some deposit quarterly (every three months) or annually (once a year).
When the interest deposits, it becomes part of your account balance immediately. If you earned $5 in interest during March and the bank deposits it on March 31, that $5 starts earning interest on April 1. This is why compounding frequency matters: the sooner interest deposits, the sooner it starts earning interest itself.
You can check when your bank deposits interest by looking at your account statements or asking customer service. The deposit will show up as a credit to your account, sometimes labeled "Interest Paid" or "Interest Deposit."
Why different banks pay different amounts of interest
Banks set their own APY based on what the Federal Reserve charges them to borrow money and what they can earn by lending money out. When the Fed raises rates, banks eventually raise the APY they offer on savings accounts. When the Fed lowers rates, banks lower APY too—sometimes quickly, sometimes slowly.
Online banks typically offer higher APY than brick-and-mortar banks because they have lower overhead costs. A traditional bank with physical branches might offer 0.01% APY while an online bank offers 4.5% APY on the same type of account. The calculation method is identical; the only difference is the rate itself.
APY can also vary based on account type. A money market account might pay more than a regular savings account. A certificate of deposit (CD) locks your money away for a set time period and usually pays more than a savings account because the bank knows it can use your money for longer.
What happens to interest if you withdraw money mid-month
If you withdraw money before the bank deposits your interest, you lose the interest that would have been calculated on that withdrawn amount. The bank calculates interest based on your balance each day, so removing money reduces the next day's calculation.
Example: your balance is $5,000 on day one. On day 15, you withdraw $2,000. The bank calculated interest on $5,000 for days 1–14, but only on $3,000 for days 15–31. You earn less interest that month because your average balance was lower.
Interest that has already been deposited into your account stays yours even if you withdraw it. If the bank deposited $5 in interest on the last day of the month and you withdraw it on the first day of the next month, that $5 is gone, but you earned it and it counted as income.
Interest earned on savings is taxable income
The interest your savings account earns is taxable income. You must report it on your tax return, and the bank must report it to the IRS if you earn more than $10 in a calendar year.
The bank will send you a 1099-INT form by January 31 of the following year, showing how much interest you earned. You'll use this form to fill out your tax return. If you have multiple savings accounts at different banks, you'll receive a separate 1099-INT from each bank, and you add them all together on your return.
The tax rate you pay on interest income depends on your overall income and tax bracket. Interest is taxed as ordinary income, not at a lower capital gains rate. If you earn $500 in interest and you're in the 22% tax bracket, you'll owe roughly $110 in federal tax on that interest (though state taxes may apply too).
Frequently Asked Questions
Does interest compound if I don't touch my account?
Yes. Compounding happens automatically every day, whether you log in or not. The bank calculates interest on your balance and adds it to your account on its regular schedule. You don't have to do anything—the interest grows on its own.
What's the difference between APY and interest rate?
APY (annual percentage yield) includes the effect of compounding, while the interest rate does not. APY is the actual amount you'll earn in a year if you leave the money untouched. Interest rate is the base rate before compounding is factored in. Banks advertise APY because it's the real number that matters to you.
Can I lose money if interest rates drop?
No. Interest rates dropping means the bank will pay you less interest on new deposits or when your rate adjusts, but you don't lose the money you already have. You earn less going forward, not less on what you've already earned.
Do I have to claim interest income if I earned less than $10?
The bank doesn't have to send you a 1099-INT if you earned less than $10, but you still owe tax on that interest if you have a tax filing requirement. It's your responsibility to report it. Check with a tax professional about whether you need to file a return.
What happens to interest if my account is closed?
Interest accrued up to the day you close the account is yours. The bank will deposit any earned interest into the account before closing it, or send it to you separately. Interest stops accruing the day the account closes.