The basic formula: multiply your balance by the APY, then divide by 365

To find out how much interest a high interest savings account will pay you, multiply your account balance by the annual percentage yield (APY), then divide by 365. That gives you the daily interest. If you want to know what you'll earn over a specific number of days, multiply the daily amount by however many days you're holding the money.

The formula is: (Balance × APY) ÷ 365 = Daily Interest. For example, if you have $10,000 in an account paying 4.50% APY, your daily interest is ($10,000 × 0.045) ÷ 365 = $1.23 per day. Over 30 days, that's $36.90.

Banks compound interest differently—some daily, some monthly—but the APY already accounts for that. The APY is what you actually earn, so you don't need to adjust for compounding yourself. What you see in the APY is the real number.

Key Takeaways

  • Multiply your balance by the APY and divide by 365 to find daily interest earned.
  • The APY shown by the bank already includes the effect of compounding, so you don't recalculate it.
  • Interest rates change, so the amount you earn next month may differ from this month even if your balance stays the same.
  • Banks round interest to the nearest cent, so your actual earnings may be a few cents different from your calculation.

Why APY matters more than the interest rate

You might see two different numbers: the interest rate and the APY. The interest rate is what the bank pays on your money. The APY is the interest rate plus the effect of compounding—interest earning interest. Because of compounding, the APY is always equal to or higher than the interest rate.

For your calculation, use the APY, not the interest rate. The APY is the real number that tells you what you'll actually earn. If a bank shows you 4.50% APY, that's the number to plug into the formula. The interest rate might be 4.48%, but that's not what matters for your math.

What changes your earnings month to month

Your balance changes, and the APY changes. If you deposit $5,000 one month and $2,000 the next, your interest that month will be different. If the Federal Reserve raises rates and your bank raises its APY from 4.50% to 4.75%, your daily interest goes up even if your balance stays the same.

Banks also sometimes pay interest on a tiered schedule—the first $25,000 earns one rate, the next $25,000 earns a lower rate. Read your account terms to see if your bank does this. If it does, you'll need to calculate interest on each tier separately and add them together.

How to find the APY your bank is actually paying

The APY should be clearly labeled on your bank's website, in your account statements, and in the account agreement. Look for the words "Annual Percentage Yield" or the abbreviation "APY." It will be a percentage like 4.50%.

If you can't find it on the main account page, check the fine print or the disclosure document. Banks are required by law to show you the APY before you open the account. If you're comparing accounts, make sure you're looking at the APY for the same account type—savings accounts, money market accounts, and certificates of deposit (CDs) often have different rates.

Using a calculator versus doing the math yourself

You can do this calculation with a basic calculator or a spreadsheet. Some banks and financial websites offer interest calculators where you enter your balance and APY and it shows you the earnings. These are accurate as long as you enter the right APY.

The advantage of doing it yourself is that you understand what's happening with your money. The advantage of using a calculator is speed, especially if you're comparing multiple accounts or running scenarios—like "what if I deposit $5,000 more?" You can change the balance and see the new number when ready.

What your actual interest payment will look like

Banks deposit interest into your account on a schedule set by their terms—usually monthly, sometimes daily or quarterly. When the interest hits your account, it becomes part of your balance, and the next interest payment is calculated on the higher amount. This is compounding in action.

Your bank statement will show each interest deposit separately, usually labeled as "Interest Paid" or "Interest Earned." The amount may be a few cents different from your calculation because banks round to the nearest cent, and they may use a slightly different day count method (some use 360 days instead of 365, though this is less common now).

How inflation affects what your interest actually buys

Interest earnings are real money, but inflation matters. If you earn 4.50% APY but inflation is running at 3%, your money is only gaining about 1.50% in purchasing power. This doesn't change how you calculate the interest, but it's worth knowing when you're deciding whether a rate is worth your time.

High interest savings accounts currently offer rates that are competitive with inflation, which is unusual. Historically, savings accounts earned less than inflation, which meant your money lost value over time. Right now, you're actually ahead. That can change when the Federal Reserve adjusts rates.

Frequently Asked Questions

Do I need to pay taxes on the interest I earn?

Yes. Interest earned in 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 interest is taxed at your ordinary income tax rate, not a special rate.

What if my bank compounds interest daily instead of monthly?

The APY already accounts for daily compounding. You don't need to recalculate. The APY is the number that reflects how often interest compounds, so using the APY in your formula gives you the right answer regardless of the compounding schedule.

Can I lock in today's APY so it doesn't go down?

No. High interest savings accounts have variable rates, which means the bank can change the APY whenever it wants. A certificate of deposit (CD) locks in a rate for a set period—three months, one year, five years—but a regular savings account does not. If rates drop, your earnings drop with them.

Is the interest I calculate before or after fees?

The interest calculation is before fees. If your bank charges a monthly maintenance fee, that comes out of your account separately. Some high interest savings accounts have no fees, which is why they're worth comparing. A $0 fee account paying 4.50% is better than a $5 fee account paying 4.50%.

What if I withdraw money mid-month—do I lose all the interest?

No. Interest is calculated daily, so you earn interest on the money you held for the days you held it. If you deposit $10,000 on the first of the month and withdraw $5,000 on the 15th, you earn interest on $10,000 for 14 days and $5,000 for the remaining days. You don't forfeit anything.