Banks multiply your balance by an annual rate, then divide by the number of times they compound per year

Interest on a savings account is calculated using your account balance, the annual interest rate the bank offers, and how often the bank compounds that interest. Most banks compound daily or monthly. The more frequently a bank compounds, the more interest you earn, because you earn interest on the interest itself.

The basic formula is: Interest = Balance × Annual Rate ÷ Number of Compounding Periods Per Year. If you keep $1,000 in an account earning 4% annual interest compounded monthly, the bank calculates roughly $3.33 in interest for that month (before the next month's compounding). The actual amount varies slightly depending on how many days are in each month and whether the bank uses a 360-day or 365-day year.

You do not need to do this math yourself. Your bank shows the interest earned in your account statement each month or each quarter. What matters is understanding that the rate advertised—called the Annual Percentage Yield, or APY—already accounts for compounding, so it tells you the real return you will see over a year.

Key Takeaways

  • Banks calculate interest by multiplying your balance by the annual rate, then dividing by how many times per year they compound interest.
  • Daily compounding earns you slightly more than monthly compounding because interest accrues on interest more often.
  • The APY shown by the bank already includes the effect of compounding, so you can compare rates between banks using APY alone.
  • Interest is added to your account automatically; you do not need to claim it or take any action to receive it.
  • The interest you earn changes month to month if the bank changes its rate, which happens when the Federal Reserve raises or lowers its benchmark rate.

Why the compounding frequency matters

Compounding is the process of earning interest on interest you have already earned. If a bank compounds daily, it calculates interest 365 times per year and adds each day's earnings to your balance. The next day's interest is then calculated on the new, slightly higher balance. Over months and years, this compounds into noticeably more money than if the bank compounded only once per year.

The difference between daily and monthly compounding on a $10,000 balance at 4% APY is roughly $3 to $5 per year—not huge, but real. The difference between daily compounding and annual compounding is larger: roughly $40 per year on the same balance. Most savings accounts now compound daily, but money market accounts and some promotional accounts may compound monthly or quarterly, so it is worth checking your account terms.

How APY differs from the stated interest rate

Banks must show you two numbers: the interest rate (sometimes called the nominal rate) and the Annual Percentage Yield, or APY. The interest rate is the raw percentage. The APY is the rate you actually earn after compounding is factored in. Because of compounding, the APY is always equal to or higher than the stated rate.

For example, a bank might advertise 3.9% interest compounded daily. The APY would be roughly 3.98%, because of the effect of daily compounding. When you compare savings accounts between banks, always use the APY, not the stated rate. The APY tells you the true return you will receive.

When and how interest is deposited to your account

Interest is added to your savings account automatically on a schedule set by your bank. Most banks deposit interest monthly or quarterly. You will see the deposit in your account statement and your available balance will increase. You do not need to do anything to receive it—no forms, no claims, no action required.

Some online banks deposit interest daily, meaning your balance grows every single day. Traditional banks often deposit monthly. The frequency does not change the total amount you earn over a year (because the APY accounts for it), but daily deposits mean you see your balance grow more visibly and more often.

How rate changes affect your interest earnings

Savings account interest rates change when the Federal Reserve raises or lowers its benchmark interest rate. When the Fed raises rates, banks typically raise the rates they offer on savings accounts within days or weeks. When the Fed lowers rates, banks lower savings rates more slowly, sometimes taking months. This is why shopping for a new account makes sense when rates are falling—your current bank may not match competitors' rates right away.

Your interest earnings will change each month if your bank changes its rate. If your bank raises the rate from 4% to 4.5%, your next month's interest will be calculated using the higher rate. If the rate drops, your interest earnings drop too. You can see the rate your bank is currently paying by logging into your account or calling customer service.

The difference between savings accounts and other deposit accounts

Savings accounts, money market accounts, and certificates of deposit (CDs) all earn interest, but the rates and compounding rules differ. Savings accounts and money market accounts have variable rates that change with the market. CDs have fixed rates that do not change for the term of the CD—usually three months to five years. Money market accounts sometimes have tiered rates, meaning you earn a higher rate if you maintain a larger balance.

High-yield savings accounts, offered mainly by online banks, earn significantly higher rates than traditional bank savings accounts because online banks have lower overhead costs. A traditional bank might offer 0.01% APY while an online bank offers 4% or higher on the same type of account. The calculation method is identical; the difference is the rate itself.

What happens if you withdraw money before interest is deposited

If you withdraw money from your savings account before the interest is deposited, you lose the interest that would have been earned on that withdrawn amount. Interest is calculated on your balance at the time the bank compounds interest. If you had $5,000 on the day the bank calculated interest, you earn interest on $5,000. If you withdraw $2,000 the next day, the interest has already been added to your account and you keep it—but next month's interest will be calculated on the lower $3,000 balance.

Some accounts have withdrawal limits or fees if you withdraw too many times per month, but these are separate from interest calculations. The interest itself is not forfeited by withdrawing; only future interest is affected because your balance is lower.

Frequently Asked Questions

Does the bank calculate interest on my minimum balance or my average balance?

Most banks calculate interest on your actual balance on the day they compound interest. A few older accounts use average daily balance, which means they add up your balance each day of the month and divide by the number of days. Check your account disclosure or call your bank to confirm which method they use. For most people with stable balances, the difference is small.

If I have multiple savings accounts at the same bank, do they earn interest separately?

Yes. Each account earns interest based on its own balance and the rate for that account type. If you have a regular savings account earning 0.01% and a high-yield savings account earning 4%, the high-yield account earns interest at the higher rate. The two accounts do not combine for interest calculation purposes.

Can I lose money in a savings account if interest rates fall?

No. Your principal—the money you deposited—is never reduced. If interest rates fall, you simply earn less interest going forward. Your balance will not shrink unless you withdraw money or incur fees. Savings accounts are insured by the FDIC up to $250,000, so your money is protected even if the bank fails.

Why do some banks show interest as "pending" before it is added to my balance?

Some banks calculate interest and show it as pending for a day or two before officially depositing it. This is normal and does not affect the amount you earn. Once the pending interest is posted, it becomes part of your balance and earns interest itself in the next compounding period.

Is the interest I earn on a savings account taxable?

Yes. Interest earned on savings accounts is taxable income. Banks send you a 1099-INT form each January if you earned $10 or more in interest during the previous year. You report this interest on your tax return. This is separate from how the bank calculates the interest itself, but it is important to know when planning your finances.