The interest you earn depends on the bank's APY, how much you have saved, and how long the money sits there
Your savings account interest is calculated using the Annual Percentage Yield (APY) the bank publishes. If you have $10,000 in an account with a 4.5% APY, you earn roughly $450 per year — but that's only if the rate stays the same for the full 12 months, which it won't. Banks change rates frequently, sometimes weekly.
The actual amount you earn depends on three things: the APY at the time your money is in the account, the balance you're holding, and how long you keep it there. If you deposit $10,000 mid-year when the rate is 4.5%, then the rate drops to 3% in month seven, you won't earn the full $450. You'll earn roughly $225 on the first six months, then less on the remaining balance at the lower rate.
Interest compounds, usually daily or monthly depending on the bank. That means you earn interest on your interest. With daily compounding at 4.5% APY, a $10,000 deposit grows to about $10,460 after one year, not $10,450. The difference is small but real.
Key Takeaways
- The APY shown on a savings account is an annual rate, but banks change it frequently — sometimes weekly — so your actual earnings will differ from the advertised rate.
- Your interest earnings equal the APY multiplied by your balance, divided by 365 (or 360, depending on the bank), then multiplied by the number of days your money was in the account at that rate.
- Interest compounds daily or monthly at most banks, meaning you earn small amounts of interest on the interest you've already earned.
- Moving money in and out of the account changes your average balance and the number of days it sits there, both of which lower your total earnings.
- High-yield savings accounts at online banks typically offer 4% to 5% APY, while traditional brick-and-mortar banks often offer under 0.5% APY on the same type of account.
How banks calculate your interest payment
Banks use a formula: Interest = (Balance × APY) ÷ 365 × Number of Days. If you have $5,000 in an account earning 4.5% APY for 30 days, you earn roughly $18.49. That calculation happens daily at most banks — they compute interest on your exact balance each day, then add it to your account monthly or quarterly.
The timing matters. If you deposit $5,000 on the 15th of the month and withdraw it on the 30th, you've only held it for 15 days. You earn interest only on those 15 days, not the full month. Some banks use a 360-day year instead of 365, which slightly reduces your earnings, though the difference is small.
When interest compounds, the bank adds your earned interest to your balance, and then calculates the next period's interest on that larger number. After one month at 4.5% APY on $10,000, you have roughly $10,037.50. In month two, you earn interest on $10,037.50, not just the original $10,000. Over a year, compounding adds up to about $10 extra on a $10,000 balance.
Why the same account earns different amounts at different banks
The APY is the only number that matters for comparing interest earnings between banks. A $10,000 deposit at 4.5% APY earns the same amount whether it's at Bank A or Bank B — roughly $450 per year, assuming the rate holds steady. The difference is that Bank A might lower its rate to 3% next month, while Bank B keeps it at 4.5% for longer.
Online banks typically offer higher APYs than traditional banks because they have lower overhead costs. A brick-and-mortar bank with physical branches might offer 0.01% APY on savings, while an online bank offers 4.5% on the same type of account. Over a year, $10,000 earns $1 at the first bank and $450 at the second. The account type is identical; the rate is the difference.
Some banks offer promotional rates for new customers — a higher APY for the first few months, then a drop to their standard rate. Read the fine print to see when the promotional period ends and what the regular rate will be.
What happens when rates change
Banks adjust savings rates based on the Federal Reserve's actions and their own business decisions. When the Fed raises its benchmark rate, banks usually raise savings APYs within days or weeks. When the Fed cuts rates, banks often cut savings rates just as quickly, sometimes faster.
You don't have to do anything when a rate changes — the new rate applies automatically to your balance going forward. If you're earning 4.5% and the bank drops to 3%, your next interest payment will be calculated at 3%. Your existing balance isn't penalized; the lower rate just applies to future earnings.
This is why comparing rates matters. If you're holding $50,000 in a savings account earning 0.5% APY, moving it to an account earning 4.5% APY means an extra $200 per year in interest. Over five years, that's $1,000 more in your account — money you earned straightforward by switching banks.
How withdrawals and deposits affect your earnings
Every time you withdraw money, your balance drops and your interest earnings drop with it. If you have $10,000 earning 4.5% APY and withdraw $5,000 mid-month, you've reduced the balance that earns interest for the rest of that month. The interest calculation only applies to the days the money was actually in the account.
Deposits work the same way. If you deposit $1,000 on the 25th of the month, that $1,000 only earns interest for the remaining days of that month. It doesn't earn interest retroactively for the days before you deposited it.
Banks calculate interest based on your daily balance, so frequent deposits and withdrawals create a lower average balance than if you left the money untouched. If you move money in and out constantly, your actual earnings will be noticeably lower than the APY suggests.
Comparing interest earnings across account types
| Account Type | Typical APY Range | Interest on $10,000 per Year | Best For |
|---|---|---|---|
| Traditional savings account | 0.01% to 0.5% | $1 to $50 | straightforward access, FDIC insured |
| High-yield savings account | 4% to 5.35% | $400 to $535 | Maximum interest, still liquid |
| Money market account | 3.5% to 5% | $350 to $500 | Interest plus check-writing |
| Certificate of Deposit (CD) | 4.5% to 5.5% | $450 to $550 | Higher rates, but money locked up |
High-yield savings accounts earn roughly 10 times more interest than traditional savings accounts at the same bank. The trade-off is usually minimal — you get the same FDIC insurance, the same access to your money, but a higher APY. The only reason to keep money in a traditional savings account is if you're already using that bank for checking and don't want to open another account.
Certificates of Deposit (CDs) often offer slightly higher rates than high-yield savings, but your money is locked up for a set term — usually three months to five years. If you withdraw early, you pay a penalty that eats into your interest earnings. CDs make sense if you know you won't need the money for a specific period.
Taxes on savings account interest
The interest you earn on a savings account is taxable income. If you earn $450 in interest over a year, that $450 is added to your taxable income for that year. The bank will send you a 1099-INT form in January showing how much interest you earned, and you report it on your tax return.
The tax you owe depends on your overall income and tax bracket. If you're in the 22% tax bracket and earn $450 in interest, you'll owe roughly $99 in federal income tax on that interest. Some states also tax interest income. This is why the real return on your savings is lower than the APY — the APY is the gross return before taxes.
If you earn less than $10 in interest during the year, the bank may not send you a 1099-INT, but you still owe tax on it if you're required to file a return. Keep your own records of interest earned.
Frequently Asked Questions
Can I earn interest on interest in a savings account?
Yes. When interest compounds, the bank adds your earned interest to your balance, and the next interest calculation includes that added amount. Daily compounding means this happens 365 times per year, though the effect is small — roughly $10 extra per year on a $10,000 balance at 4.5% APY.
What's the difference between APY and APR on a savings account?
APY includes the effect of compounding; APR does not. For savings accounts, always look at the APY because it shows your actual earnings. APR is used for loans and credit cards, where it works differently.
Do I lose interest if I withdraw money before the end of the month?
No, but you only earn interest for the days the money was in the account. If you deposit $5,000 on the 20th and withdraw it on the 25th, you earn interest for five days, not the full month. Interest is calculated daily at most banks.
Why is my interest payment smaller than I expected?
The most common reason is that the APY changed during the month, or your balance was lower than you thought due to pending transactions. Banks also use different compounding schedules — some compound daily, others monthly. Check your statement to see the exact APY used and your average daily balance.
Should I move my savings to a high-yield account?
If your current account earns less than 1% APY and you have more than a few thousand dollars saved, moving to a high-yield account earning 4% to 5% will earn you significantly more interest with no downside — the money is still liquid and FDIC insured. The only reason not to move is if you value the convenience of keeping everything at one bank.