The amount you earn depends on the bank's APY, your balance, and how long the money sits there
Interest on a savings account is calculated by multiplying your balance by the annual percentage yield (APY) the bank offers, then dividing by the number of days in a year. If you keep $10,000 in an account with a 4.5% APY for a full year, you earn $450. If you keep it for six months, you earn roughly $225. The catch: most banks compound interest daily or monthly, meaning you earn small amounts of interest on the interest itself—but the difference is usually a few dollars a year on typical balances.
The real variable is the APY itself. Banks set their own rates based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, new savings accounts often offer higher APYs within weeks. When the Fed cuts rates, banks lower their APYs just as fast. A savings account at one bank might pay 4.75% while another pays 1.5%—same economy, same Federal Reserve rate, completely different earnings. This is why the bank you choose matters far more than the size of your balance.
Interest posts to your account on a schedule the bank sets: some add it daily, some monthly, some quarterly. You don't have to do anything to receive it—the bank calculates and deposits it automatically. If you withdraw money before interest posts, you lose the interest that would have been earned on that withdrawn amount.
Key Takeaways
- Interest earned equals your balance multiplied by the APY, divided by 365 days, then multiplied by the number of days your money was in the account.
- APY varies widely between banks—shopping around can mean earning $200 to $400 more per year on a $10,000 balance.
- Interest compounds daily or monthly at most banks, so you earn small amounts on your interest, but the effect is modest on balances under $50,000.
- The bank deposits interest automatically on its own schedule; you earn it whether you check your account or not.
- Withdrawing money before interest posts means you forfeit the interest that would have been earned on the withdrawn amount.
How banks calculate the interest you earn
The formula is straightforward: Balance × APY ÷ 365 × Number of Days = Interest Earned. If you have $5,000 at 4.0% APY for 90 days, the math is $5,000 × 0.04 ÷ 365 × 90 = $49.32. Most banks do this calculation daily, so the interest compounds—meaning tomorrow's interest calculation includes today's interest in the balance.
Compounding makes a real difference only on larger balances or over longer periods. On $10,000 at 4.5% APY compounded daily versus simple interest (no compounding), you earn about $4.50 more per year. On $100,000, the difference is roughly $45 per year. For most people with typical savings balances, compounding adds up to pocket change. But it is assistance programs, so banks advertise it heavily.
Some banks calculate interest monthly instead of daily. This means your balance on the last day of the month determines how much interest you earn for that entire month. If you deposit $5,000 on the first of the month and withdraw it on the 15th, you earn interest only on the full $5,000 for one month, not on the declining balance. Monthly compounding is less common now—most online banks switched to daily compounding to attract customers.
Why the same APY produces different earnings at different banks
The APY is the rate; the interest is what you actually receive. Two banks offering 4.5% APY will pay you the same amount if your balance and time frame are identical. The difference comes from when interest posts and how the bank handles deposits and withdrawals mid-cycle.
Some banks use the "average daily balance" method: they add up your balance at the end of each day for the month, divide by the number of days, and calculate interest on that average. Others use the "daily balance" method: they calculate interest on your actual balance each day and compound it. The daily balance method almost always pays slightly more, especially if your balance fluctuates.
A few banks still use the "low balance" method, which calculates interest on your lowest balance during the month. This is rare now and almost always paired with a low APY, so it is not worth your time to find. Stick with banks that advertise daily compounding—it is the standard at reputable online banks.
How long it takes for interest to show up in your account
Interest posts on a schedule set by the bank, not by you. Most online banks post interest monthly on the first or last day of the month. Some post quarterly. A few post daily, though the interest amount is so small daily that it barely matters. Check your bank's terms to know when to expect it.
Once interest posts, it is yours—the bank cannot take it back. If you withdraw the interest, you lose it, but the principal balance remains untouched. If you leave the interest in the account, it becomes part of your balance and earns interest itself the next cycle.
Interest does not post if your account is closed. If you close a savings account mid-month, the bank calculates interest up to the closure date and deposits it into your linked checking account or mails you a check. Read the closure confirmation to see where your final interest payment went.
What happens to interest when you withdraw money
If you withdraw money before interest posts, you lose the interest that would have been earned on that amount. If you have $10,000 earning 4.5% APY and you withdraw $5,000 on day 15 of a 30-day month, you earn interest only on the $10,000 for 15 days and the $5,000 for the remaining 15 days—not on the full $10,000 for the entire month.
Some savings accounts have withdrawal limits or penalties if you exceed them. Federal Regulation D once capped savings account withdrawals at six per month, but that rule was suspended in 2020 and has not been reinstated. Most banks now allow unlimited withdrawals, though a few still impose fees after a certain number. Check your account terms before opening.
Money market accounts and certificates of deposit (CDs) have stricter withdrawal rules. A CD locks your money for a set term—three months, one year, five years—and charges an early withdrawal penalty if you take it out before the term ends. The penalty usually equals several months of interest. Savings accounts have no such penalty; you can withdraw anytime.
How APY changes affect what you earn
When the Federal Reserve raises its benchmark rate, banks typically raise their savings APYs within one to four weeks. When the Fed cuts rates, banks cut their APYs just as fast—sometimes within days. Your existing balance earns the new rate immediately; you do not have to do anything.
If you locked money into a CD before rates rose, you are stuck with the old rate until the CD matures. This is the trade-off: CDs pay slightly more than savings accounts because your money is locked up, but if rates rise, you cannot move to a higher rate without paying a penalty. Savings accounts let you move your money to a higher-paying bank anytime.
Rate changes are retroactive to your account, not to your earnings. If you earned $100 in interest at 4.0% APY and the bank raises the rate to 5.0%, your next interest payment reflects the new 5.0% rate. The $100 you already earned stays yours.
Comparing interest earnings across different account types
| Account Type | Typical APY Range | Compounding | Withdrawal Rules |
|---|---|---|---|
| High-yield savings | 4.0% to 5.5% | Daily | Unlimited |
| Regular savings | 0.01% to 0.5% | Daily or monthly | Unlimited |
| Money market account | 4.0% to 5.5% | Daily | Usually 6 per month (varies) |
| 3-month CD | 4.5% to 5.75% | Daily | Locked; early withdrawal penalty |
| 1-year CD | 4.5% to 5.75% | Daily | Locked; early withdrawal penalty |
High-yield savings accounts and money market accounts pay the most interest because they are offered by online banks or online divisions of brick-and-mortar banks with lower overhead. A regular savings account at a traditional bank pays almost nothing—often 0.01% or less—because the bank keeps most of the interest for itself.
CDs pay slightly more than high-yield savings accounts because your money is locked up for a set term. The longer the term, the higher the rate—a five-year CD might pay 5.5% while a three-month CD pays 4.75%. But if you need the money early, the penalty can wipe out years of interest, so only lock money into a CD if you are certain you will not need it.
Frequently Asked Questions
How much interest will I earn on $10,000 in a savings account?
At a 4.5% APY, you earn $450 per year, or about $37.50 per month. At a 0.5% APY (typical for traditional banks), you earn $50 per year. The bank you choose determines the APY, so shopping around can mean earning $400 more per year on the same $10,000 balance.
Do I have to pay taxes on savings account interest?
Yes. Interest is taxable income. Banks send you a 1099-INT form if you earn $10 or more in interest during the year. You report this on your tax return. The interest is taxed at your ordinary income tax rate, not at a capital gains rate.
Can a bank lower my APY without warning?
Yes. Banks can change APY anytime, and most do not require advance notice. They usually notify you by email or through your online account, but the change takes effect immediately. If your rate drops and you want a higher rate, you can move your money to another bank.
What is the difference between APY and interest rate?
The interest rate is the annual percentage the bank pays on your balance. APY includes the effect of compounding—how often interest is calculated and added back to your balance. APY is always equal to or higher than the interest rate. Banks advertise APY because it is the true annual return you receive.
Do I lose interest if I close my savings account?
You lose interest only if you close the account before interest posts for that period. Once interest posts, it is yours. If you close mid-month, the bank calculates interest through the closure date and deposits it into your linked account or mails you a check.