The interest you earn depends on the APY, your balance, and how long the money sits there
The amount of interest a savings account earns is not fixed—it changes based on three things: the annual percentage yield (APY) your bank offers, how much money you keep in the account, and how long it stays there. A bank advertising 4.50% APY will pay you more interest than one offering 0.01% APY, even if you deposit the same amount. The difference between these two rates can mean hundreds of dollars per year on a $10,000 balance.
Interest compounds, which means you earn interest on the interest you already earned. Most savings accounts compound daily or monthly. If your account compounds daily, the bank calculates interest every single day and adds it to your balance, so the next day's interest is slightly higher. This compounding effect is small at first but grows over months and years.
You can estimate your earnings with a simple formula: multiply your balance by the APY, then divide by the number of days in a year (365). For example, $10,000 at 4.50% APY earns roughly $450 per year if the balance stays constant. But because interest compounds, you will actually earn slightly more than that—usually a few dollars more depending on how often the bank compounds.
Key Takeaways
- Interest earned is calculated by multiplying your account balance by the APY your bank offers, divided by 365 days.
- Banks compound interest daily, weekly, or monthly, meaning you earn interest on interest already credited to your account.
- A higher APY makes a real difference: 4.50% APY on $10,000 earns roughly $450 per year, while 0.50% APY earns roughly $50 per year on the same balance.
- Interest rates change over time and vary by bank, so the APY you see today may not be the same six months from now.
- Money you withdraw before the end of a compounding period may not earn the full interest for that period, depending on your bank's rules.
How compounding frequency affects your total earnings
The more often a bank compounds interest, the more you earn. Daily compounding is better than monthly compounding, which is better than annual compounding. The difference is usually small—a few dollars per year on a typical balance—but it adds up over time.
If a bank compounds daily, it divides the APY by 365, calculates interest on your current balance, and adds it immediately. The next day, you earn interest on that new, slightly higher balance. Monthly compounding does the same thing but only once per month, so you miss out on the compounding that happens in between.
Most online banks and credit unions compound daily. Traditional brick-and-mortar banks often compound monthly or quarterly. Check your account disclosure or call the bank to find out which method yours uses. The disclosure document should list the compounding frequency and the APY.
Why APY matters more than the interest rate alone
APY (annual percentage yield) already includes the effect of compounding, so it is the true number to compare between banks. The interest rate alone does not tell you the full story. A bank might advertise a 4.48% interest rate that compounds daily, which becomes 4.59% APY. Another bank might advertise 4.50% APY, which is already the final number after compounding is factored in.
Always compare APY, not the interest rate. The APY is what you will actually earn over a year if you leave the money untouched. Banks are required to disclose the APY prominently on savings account pages and in account agreements.
How withdrawals and deposits change your earnings
Interest is calculated on your average daily balance or your ending balance, depending on the bank. If your bank uses average daily balance, it adds up your balance at the end of each day during the compounding period, divides by the number of days, and calculates interest on that average. If it uses ending balance, it only looks at what you have on the last day of the period.
This matters when you withdraw money. If you withdraw $5,000 midway through a month and your bank uses average daily balance, you will earn interest on the full amount for part of the month and the reduced amount for the rest. With ending balance, you earn interest only on what remains at month's end.
Deposits work the same way. Money you deposit partway through a compounding period starts earning interest immediately, but you will not earn a full period's worth of interest on it until the next period begins.
Real examples of interest earned at different rates
| Balance | APY | Approximate Annual Interest | Approximate Monthly Interest |
|---|---|---|---|
| $1,000 | 0.50% | $5 | $0.42 |
| $1,000 | 4.50% | $45 | $3.75 |
| $10,000 | 0.50% | $50 | $4.17 |
| $10,000 | 4.50% | $450 | $37.50 |
| $50,000 | 4.50% | $2,250 | $187.50 |
These figures assume the balance stays constant and the APY does not change. In reality, APY fluctuates based on what the Federal Reserve does with interest rates. When the Fed raises rates, banks typically raise their APY on savings accounts within weeks. When the Fed cuts rates, banks usually cut their APY as well, though sometimes more slowly.
Why savings account rates change
Banks do not set APY on their own. They respond to the federal funds rate, which is the interest rate the Federal Reserve sets for banks to lend to each other overnight. When the Fed raises the federal funds rate, banks have more incentive to offer higher APY to attract deposits. When the Fed cuts the rate, banks lower their APY because they do not need to compete as hard for deposits.
This means the 4.50% APY you see today might be 3.75% in six months if the Fed cuts rates. Or it might stay the same if the Fed holds steady. You cannot predict this, but you can watch what the Fed does and expect your bank's APY to follow within a few weeks.
Some banks move faster than others. Online banks often raise or lower APY within days of a Fed move. Traditional banks sometimes take weeks or months. If you want to lock in a higher rate, high-yield savings accounts at online banks tend to move first.
Where to find your account's APY and compounding details
Your bank must disclose the APY and compounding frequency in writing. Look for the Truth in Savings Act Disclosure or Account Disclosure document, which banks provide when you open an account or upon request. This document lists the APY, the compounding frequency, and the method used to calculate interest (average daily balance or ending balance).
You can also find the APY on your bank's website, usually on the savings account product page. Call the bank's customer service line if you cannot find it online. Ask specifically for the APY and how often interest compounds.
Your monthly or quarterly statement will show the interest you earned during that period. Add up the monthly interest amounts to estimate your annual earnings, though the actual total will be slightly higher because of compounding.
Frequently Asked Questions
Does interest compound on money I just deposited?
Yes, interest starts accruing immediately on new deposits. However, you will not see the first interest payment until the end of the compounding period. If your bank compounds daily and you deposit money on a Tuesday, you earn interest that day, but it may not show up in your account until the end of the month when all daily interest is credited at once.
What happens to my interest if I withdraw money before the end of the month?
You keep the interest you have already earned. If your bank uses average daily balance, you earn interest on the full amount for the days you held it, then on the reduced amount after withdrawal. If it uses ending balance, you earn interest only on what remains at the end of the period.
Can I lose money in a savings account?
No. A savings account earns interest or stays flat; it does not go down. Even at 0.01% APY, you earn something. Your balance can only decrease if you withdraw money yourself or if the bank charges fees that exceed your interest earnings.
Why do some banks offer much higher APY than others?
Online banks have lower overhead costs than brick-and-mortar banks, so they can afford to offer higher APY to attract deposits. Traditional banks with physical branches often offer lower rates because they spend more on staff and real estate. The money is equally safe at either type of bank if it is insured by the FDIC.
If I move my money to a different bank, do I lose the interest I earned?
No. Interest that has already been credited to your account is yours to keep. When you transfer the money, you move the full balance including all interest earned. You will not earn interest during the transfer itself, which usually takes one to three business days.