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. The bank keeps the difference between what it pays you and what it charges borrowers. That payment to you is interest.
The amount you earn depends on three things: how much money sits in the account, how long it stays there, and the interest rate the bank offers. A higher rate means more money back. A longer time in the account means more days the interest can accumulate. The bank calculates this daily or monthly, depending on the account terms.
Interest rates on savings accounts change. Banks set their own rates based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, banks usually raise savings rates too — sometimes within days, sometimes over weeks. When the Fed cuts rates, savings rates typically fall. You will not see a notice; the rate just changes in your account terms.
Key Takeaways
- Interest is calculated on your account balance, and the rate varies by bank and account type — high-yield savings accounts typically pay more than standard savings accounts.
- Banks compound interest daily or monthly, meaning you earn interest on the interest you already earned, which accelerates growth over time.
- Your interest rate can change at any time because banks adjust rates when the Federal Reserve moves its benchmark rate.
- The amount you actually earn depends on your balance, how long the money stays in the account, and the stated annual percentage yield (APY).
How the bank calculates what you earn each day
Banks use a formula based on your balance, the interest rate, and the number of days the money has been in the account. Most savings accounts use daily compounding, which means the bank calculates interest on your balance each day, then adds that interest to your account. The next day, the bank calculates interest on the new, larger balance — including the interest from yesterday.
Here is a concrete example. Suppose you have $10,000 in a savings account with a 4.50% annual percentage yield (APY), and the bank compounds daily. On day one, the bank calculates one day's worth of interest: $10,000 × 0.045 ÷ 365 = $1.23. That $1.23 gets added to your account. On day two, the bank calculates interest on $10,001.23, not $10,000. Over a year, that compounding effect means you earn slightly more than straightforward multiplication would suggest.
Some accounts compound monthly instead of daily. Monthly compounding means you earn less, because the bank only adds interest once a month rather than every day. The difference is small on modest balances but becomes visible on larger amounts or over many years.
Why the APY matters more than the interest rate
Banks list two numbers: the interest rate and the annual percentage yield (APY). The interest rate is the raw percentage. The APY includes the effect of compounding — it shows what you actually earn in a year if you do not withdraw money.
A bank might advertise a 4.50% interest rate with 4.60% APY. That 0.10% difference is the compounding effect. On $10,000, that gap costs you about $10 per year. On $100,000, it costs about $100. Always compare APYs when choosing between accounts, not the advertised interest rate.
The APY also assumes you leave the money untouched for the full year. If you withdraw money partway through, you earn less because the balance was lower for part of the period.
What happens when you withdraw money before the interest posts
Interest does not post to your account on a fixed schedule. Most banks calculate and add interest daily, but some do it monthly. If you withdraw money before the interest is added, you lose the interest you earned on that money for that period.
For example, suppose your account compounds daily and you have $10,000 on Monday. You earn about $1.23 in interest that day. On Tuesday morning, before the bank posts the interest, you withdraw $5,000. The bank will still add the $1.23 to your account — you earned it on Monday. But starting Tuesday, you only earn interest on the remaining $5,000, so your daily interest drops to about $0.62.
Some savings accounts have withdrawal limits or penalties if you take money out too often. Check your account terms before opening. Most standard savings accounts allow six withdrawals per month without penalty, though this rule varies by bank.
How interest rates change and what that means for your money
Your interest rate is not locked in. Banks change rates whenever they choose, and they usually move in the same direction as the Federal Reserve. When the Fed raises its benchmark rate, banks typically raise savings rates within days or weeks. When the Fed cuts rates, savings rates fall — sometimes when ready.
You will not receive a notice before the change. The rate straightforward updates in your account terms. You can check your current rate by logging into your online banking portal or calling the bank. If your rate drops and you want a higher rate, you can move your money to a different bank — there is no penalty for closing a savings account and opening one elsewhere.
High-yield savings accounts tend to raise rates faster than traditional savings accounts when the Fed moves up, and they often pay 4% to 5% APY during periods of higher Fed rates. Standard savings accounts at large banks often pay 0.01% to 0.05% APY. The difference compounds significantly over time.
How much interest you actually earn depends on your balance and time
The formula is straightforward: Interest = Balance × APY ÷ 365 × Number of Days. A larger balance earns more. Money that sits longer earns more. A higher APY earns more.
Here are three scenarios with $10,000 at different rates and timeframes:
| APY | Time in Account | Interest Earned |
|---|---|---|
| 0.05% (typical bank savings) | 1 year | $5 |
| 4.50% (high-yield savings) | 1 year | $450 |
| 4.50% (high-yield savings) | 6 months | $225 |
The difference between 0.05% and 4.50% is $445 per year on $10,000. That gap widens with larger balances. On $100,000, the difference is $4,450 per year. This is why the interest rate you choose matters — it directly affects how much your money grows.
Interest is taxable income
The interest you earn is taxable income. At the end of each year, your bank sends you a Form 1099-INT listing the interest you earned. You report this on your tax return as income. The amount of tax you owe depends on your tax bracket and total income.
If you earned $450 in interest and you are in the 22% tax bracket, you owe roughly $99 in federal tax on that interest. This is one reason high-yield savings accounts matter: earning 4.50% instead of 0.05% gives you more interest to work with, even after taxes.
Some people move money between accounts to manage tax liability, but for most people, the interest earned on a savings account is small enough that it does not significantly change their tax situation. Keep your 1099-INT when you receive it, and report the number on your tax return.
Frequently Asked Questions
Can I lose money if the interest rate drops?
No. Your balance stays the same. If your interest rate drops from 4.50% to 3.00%, you still have the full amount you deposited. You just earn less interest going forward. The money you already earned stays in your account.
What is the difference between a savings account and a money market account?
Money market accounts often pay slightly higher interest rates than savings accounts, but they usually require a larger minimum balance and limit how often you can withdraw. Both are FDIC insured up to $250,000. The interest calculation works the same way in both.
Do I earn interest on interest?
Yes, through compounding. When the bank adds interest to your account, that interest becomes part of your balance. The next period, you earn interest on the original balance plus the interest you already earned. This is why compounding matters — it accelerates growth over time.
What happens to my interest if I move my money to a different bank?
You keep all the interest you earned up to the day you withdraw. The old bank calculates interest through the withdrawal date and includes it in the amount you transfer. You do not lose any interest by switching banks.
Why do some banks pay more interest than others?
Banks set their own rates based on their business model and funding costs. Online banks typically pay higher rates because they have lower overhead than brick-and-mortar branches. Large national banks often pay lower rates because they have more deposits and less need to attract new customers. Shop around — rates vary significantly.