The amount you earn depends on the account's APY, how much you deposit, and how long the money sits there
Your savings account interest comes from one number: the annual percentage yield (APY), which your bank publishes and can change at any time. The formula is straightforward: multiply your account balance by the APY, divide by 365, and multiply by the number of days the money stayed in the account. A $10,000 balance at 4.5% APY earns roughly $450 per year, or about $1.23 per day. But that calculation only works if your balance never changes and the rate never changes—which almost never happens.
Most savings accounts compound interest daily or monthly, meaning you earn interest on the interest you already earned. This compounds your growth slightly, but the effect is small on typical balances. The real variables are the APY itself (which varies wildly between banks), how much you keep in the account, and whether you add or withdraw money during the year.
Key Takeaways
- Interest earned = (balance × APY) ÷ 365 × number of days, though most banks calculate this daily and compound the result monthly or quarterly.
- APY varies from under 0.01% at some large banks to over 5% at online banks and credit unions, so switching banks can double or triple your earnings on the same balance.
- If you deposit $5,000 and withdraw $2,000 three months later, you only earn interest on the actual balance each day, not the full $5,000 for the whole year.
- Banks can lower the APY without notice, so the rate you see today may not be the rate you earn next month.
How banks calculate daily interest and compound it
Banks calculate interest by dividing your APY by 365 (or sometimes 360, depending on their method) and applying that daily rate to your balance each day. If you have $10,000 at 4.5% APY, the daily rate is 0.0123% (4.5% ÷ 365). On day one, you earn $1.23. On day two, if your balance is still $10,000, you earn another $1.23.
When the bank compounds interest, it adds that $1.23 back into your account, so on day three you earn interest on $10,001.23, not just $10,000. The difference is tiny at first—you earn about $0.00017 extra—but it adds up over months and years. Monthly compounding is more common than daily, so the interest sits in a separate ledger until the end of the month, then gets added all at once.
The APY already accounts for compounding, so you do not need to calculate it yourself. The bank's statement will show you exactly how much interest posted each month. If you want to estimate for the year ahead, multiply your current balance by the APY and divide by 12 for a rough monthly figure—but only if the balance and rate stay the same, which they rarely do.
Why the same balance earns different amounts at different banks
A $50,000 savings account earns roughly $2,500 per year at a 5% APY bank, but only $50 per year at a 0.1% APY bank. That $2,450 difference comes entirely from the APY, not from any difference in how the banks calculate or compound interest. Large national banks often offer rates below 0.5%, while online banks and some credit unions offer 4% to 5.5% on regular savings accounts.
The reason for this gap is cost. Online banks have lower overhead than brick-and-mortar branches, so they can afford to pay depositors more. Large banks rely on checking account fees and loan interest to make money, so they do not need to compete on savings rates. Credit unions are member-owned and often prioritize member returns over profit, which is why their rates tend to be higher.
Switching your $50,000 from a 0.1% account to a 5% account means earning an extra $2,450 per year with zero additional effort. This is one of the few financial moves where the math is simple and the payoff is real. The catch is that high-yield rates can drop quickly when the Federal Reserve cuts rates, so a 5% account today might be 3% in six months.
How deposits and withdrawals change your total interest
Interest is calculated on your balance each day, so the timing and size of deposits and withdrawals matter. If you deposit $10,000 on January 1 and leave it untouched for a year at 4.5% APY, you earn about $450. But if you deposit $10,000 on January 1, withdraw $5,000 on July 1, and leave the remaining $5,000 for the rest of the year, you earn roughly $300 instead—$225 on the full $10,000 for six months, plus $112.50 on the remaining $5,000 for six months.
Banks track your balance every single day. If you deposit money on the 15th and withdraw it on the 20th, you earn interest for only six days on that deposit. This is why moving money in and out frequently reduces your total interest earned. If you are saving for a goal and plan to withdraw the money in a few months, a high-yield savings account still beats a regular savings account, but you will earn less than if you left the money alone for a full year.
Some people use this to their advantage by moving money between accounts strategically—for example, keeping a large balance in a high-yield account and moving smaller amounts to a checking account as needed. The interest loss from the withdrawal is usually small compared to the gain from the higher rate, so this often makes sense.
When banks change rates and how it affects your earnings
Banks can change the APY on savings accounts at any time without notice. When the Federal Reserve raises rates, banks usually raise savings rates within days or weeks to stay competitive. When the Fed cuts rates, banks often cut savings rates much faster—sometimes within hours. This means a 5% account today could be 4% next month if the Fed signals a rate cut.
Your bank will notify you of a rate change, usually by email or through your online account portal, but the notification often comes after the change takes effect. You have no right to lock in a rate for a year on a regular savings account—that is what certificates of deposit (CDs) are for. If you want to protect your rate, you would need to move your money to a CD, which locks the rate but also locks your money for a set period (usually three months to five years).
The practical takeaway: if you see a high rate, do not assume it will last. Banks that offer 5% rates are usually trying to attract new deposits, and they often lower the rate once they have enough money. Check your rate quarterly and be ready to move your money if a better option appears elsewhere.
Comparing interest earnings across different account types
A regular savings account at a large bank might earn 0.01% to 0.5% APY. A high-yield savings account at an online bank might earn 4% to 5.5%. A money market account (which is similar to a savings account but may require a higher minimum balance) might earn 4% to 5%. A CD with a one-year term might earn 4.5% to 5.5%, but your money is locked away and you pay a penalty if you withdraw early.
On a $25,000 balance for one year, here is what the difference looks like:
| Account Type | Typical APY | Interest Earned (Year 1) |
|---|---|---|
| Large bank savings | 0.1% | $25 |
| High-yield savings | 4.5% | $1,125 |
| One-year CD | 5% | $1,250 |
The choice between these depends on when you need the money. If you might need it within a year, a high-yield savings account is better because you can withdraw anytime without penalty. If you know you will not touch it for a year, a CD locks in a slightly higher rate and protects you if rates fall. If you need the money in three months, a three-month CD might offer 4.8% while a savings account offers 4.5%, so the CD wins even though the term is short.
Taxes on savings account interest
Interest earned in a savings account is taxable income. If you earn $1,000 in interest during the year, you must report it on your tax return. Your bank will send you a 1099-INT form in January showing how much interest you earned, and you report that amount on your federal tax return.
The tax rate depends on your overall income and tax bracket. If you are in the 22% tax bracket and earn $1,000 in interest, you will owe roughly $220 in federal taxes on that interest (plus any state taxes). This is why the after-tax return matters more than the headline APY. A 5% APY account earning $1,000 in interest becomes $780 after taxes if you are in the 22% bracket.
Some people use tax-advantaged accounts like IRAs or 529 plans to earn interest without paying taxes on it each year, but those accounts have contribution limits and withdrawal restrictions. For most people saving in a regular savings account, the interest is taxable, and you should factor that into your decision about where to keep the money.
Frequently Asked Questions
How often do banks pay interest into my account?
Most banks compound and post interest monthly, meaning the interest is calculated daily but added to your account once a month. Some banks post quarterly or even annually. Check your account agreement or call your bank to confirm the schedule. The more frequently interest is compounded, the slightly more you earn, but the difference is usually small.
Can I earn interest on money I just deposited?
Yes, interest starts accruing the day the deposit clears, not the day you make the deposit. If you deposit money on a Friday and it clears on Monday, you start earning interest on Monday. Transfers between your own accounts at the same bank usually clear instantly, while transfers from other banks take one to three business days.
What happens to my interest if I close the account before the end of the month?
You keep the interest you have already earned up to the day you close the account. If you close on the 15th and the bank posts interest on the 30th, you will not receive the interest for the second half of the month. Some banks pay out accrued interest when you close; others do not. Ask before you close.
Is there a maximum amount of interest I can earn?
No. The more money you deposit, the more interest you earn. There is no cap on interest earnings in a savings account. However, the Federal Deposit Insurance Corporation (FDIC) insures only up to $250,000 per depositor per bank, so if you have more than that, you should split it across multiple banks to keep it all insured.
Why is my interest so low even though the APY looks decent?
The most common reason is that your balance is small or you withdrew money partway through the month. Interest is calculated on your actual daily balance, so a $1,000 balance earns much less than a $10,000 balance. Also, if the APY recently dropped, you may be earning the old rate on money deposited before the change and the new rate on money deposited after.