Banks multiply your balance by an annual rate, then divide by the number of days in the year to find what you earn each day

Most savings accounts use daily compounding. The bank takes your account balance at the end of each day, multiplies it by the annual interest rate, divides by 365 (or 360, depending on the bank), and adds that amount to your account. The next day, interest is calculated on the new, slightly higher balance. This repeats every single day.

The result is that you earn interest on your interest. If you start with $1,000 at 4.50% annual rate, you earn roughly $45 in year one—but because the balance grows each day, you earn slightly more than if the bank just paid you $45 at the end of the year in one lump sum.

The exact formula banks use is: Daily Interest = (Account Balance × Annual Rate) ÷ 365. Some banks use 360 days instead of 365, which slightly increases what you earn. The difference is small but real over months and years.

Key Takeaways

  • Daily compounding means interest is calculated and added to your account every single day, not just once a year.
  • The annual percentage yield (APY) you see advertised already accounts for compounding, so it shows the true amount you will earn over a year.
  • Higher balances earn more interest each day, and that interest itself earns interest the next day.
  • The bank's choice to use 365 or 360 days in the calculation makes a small but measurable difference over time.

The difference between APR and APY

Banks advertise two different rates, and they are not the same. The annual percentage rate (APR) is the raw interest rate without compounding factored in. The annual percentage yield (APY) includes the effect of daily compounding.

If a bank offers 4.50% APR on a savings account, the APY will be slightly higher—often around 4.60% or 4.61%—because you earn interest on your interest throughout the year. The difference grows larger as rates rise. At 5.00% APR, the APY might be 5.12%. Always compare APY when shopping for accounts, because that is the number that tells you what you actually earn.

Your bank statement or online account dashboard will show APY, not APR. That is the rate that matters for your money.

How often interest posts to your account

Interest is calculated daily, but it does not post (actually appear in your balance) every day. Most banks post interest monthly, on the last day of the month or the first day of the next month. Some post quarterly. A few high-yield accounts post daily.

The timing of posting does not change how much you earn—the daily calculation still happens whether you see it or not. But it does affect when you can withdraw the interest or when it starts earning interest itself. If your bank posts monthly, the interest you earned in the first week of the month does not start earning its own interest until the posting date.

Check your account details or call your bank to find out when interest posts. It is usually in the fine print of your account agreement.

Why your interest rate can change

Savings account rates are not locked in. Banks set their own rates based on what the Federal Reserve does and what competitors offer. When the Fed raises its benchmark rate, banks usually raise savings rates within days or weeks. When the Fed cuts rates, banks cut savings rates just as fast.

Your current rate is may provide only for as long as your bank chooses to keep it. You might see your rate drop from 4.50% to 4.25% with no warning. Some banks notify customers by email or mail; others post the change on their website. Read your account agreement to see what notice period your bank promises.

If your rate drops and you do not like the new rate, you can move your money to a different bank. There is no penalty for closing a savings account and opening one elsewhere, though you should check whether your new bank has any minimum balance requirements.

How minimum balances affect what you earn

Some savings accounts require you to keep a minimum balance to earn the advertised rate. Common minimums are $500, $1,000, or $2,500. If your balance falls below the minimum, the bank may drop your rate to something much lower—sometimes 0.01% or less.

Other accounts have no minimum at all. High-yield savings accounts at online banks typically have no minimum balance requirement and pay the same rate whether you have $100 or $100,000 in the account.

Before opening an account, check whether there is a minimum balance and what happens if you fall below it. If you have a small amount to save, a no-minimum account is usually the better choice.

How fees reduce your earnings

Monthly maintenance fees, overdraft fees, or inactivity fees can wipe out your interest earnings. A $10 monthly fee on an account earning $3 per month in interest means you are actually losing $7 that month.

Most online banks and many brick-and-mortar banks have eliminated monthly fees on savings accounts. But some still charge them, especially if you do not meet a minimum balance or if you make too many withdrawals. Read the fee schedule before you open an account.

If your current bank charges a monthly fee and you are earning less interest than the fee costs, switching to a no-fee account will immediately increase your net earnings.

What happens to interest when you withdraw money

Interest is calculated on your balance at the end of each day. If you withdraw money mid-month, you stop earning interest on that amount immediately. The interest you already earned stays in your account, but future daily calculations use the lower balance.

For example, if you have $5,000 earning 4.50% APY and you withdraw $2,000 on the 15th of the month, you earn interest on $5,000 for the first 14 days and on $3,000 for the remaining days. You do not lose the interest you already earned—it stays in your account and compounds with the remaining balance.

Some savings accounts limit how many withdrawals you can make per month without a fee. Check your account rules before you open it, especially if you plan to move money in and out frequently.

Frequently Asked Questions

Does interest compound if I do not touch my account?

Yes. Compounding happens automatically every day, whether you log in or not. You do not have to do anything. The bank calculates interest on your balance, adds it to your account, and then calculates interest on that new balance the next day.

What if my bank uses 360 days instead of 365?

You earn slightly more interest. Using 360 days makes the daily rate higher, so each day's interest is a bit larger. Over a year, the difference is small—usually a few dollars on a $10,000 balance—but it adds up. Ask your bank which method it uses.

Can I predict exactly how much interest I will earn?

Not precisely, because the rate can change and the exact number of days varies. But you can estimate: multiply your balance by the APY and divide by 12 for a rough monthly figure. For a $10,000 balance at 4.50% APY, expect around $37 to $38 per month, though the actual amount will vary slightly.

Do I pay taxes on savings account interest?

Yes. Interest earned on a savings account is taxable income. Your bank will send you a 1099-INT form at tax time if you earned $10 or more in interest during the year. You report this on your tax return. The amount is small for most people, but it still counts as income.

Is there a limit to how much interest I can earn?

No. There is no cap on interest earnings. The more money you keep in the account and the higher the rate, the more you earn. Some banks do have maximum balance limits for certain account types, but these are rare and usually only apply to special promotional rates.