Interest grows based on your balance, the rate your bank offers, and how often the bank compounds it

Interest in a savings account is money the bank pays you for keeping your money there. The amount you earn depends on three things: how much you have saved, what annual percentage yield (APY) the bank advertises, and how frequently the bank adds interest to your account—usually daily, monthly, or quarterly.

The math is straightforward: a higher balance earns more, a higher APY earns more, and more frequent compounding (when the bank adds interest to your balance, then pays interest on that interest) earns slightly more over time. Most savings accounts compound daily, which means interest accrues every single day, even though you may only see it posted to your account once a month.

The real difference between accounts comes down to APY. A high-yield savings account at an online bank might offer 4.5% APY, while a traditional brick-and-mortar bank might offer 0.01%. On a $10,000 balance, that gap means earning roughly $450 per year versus $1 per year. The APY is what matters most—not the bank's name or how many branches it has.

Key Takeaways

  • Interest earned equals your balance multiplied by the APY, divided by 365 days (or 360, depending on the bank), then compounded daily or at whatever interval your bank uses.
  • Compounding means the bank pays interest on your interest, so your balance grows slightly faster than simple multiplication would suggest.
  • APY is the only number that matters when comparing accounts—it already accounts for how often interest compounds.
  • Moving money to a high-yield savings account can earn you 100 to 400 times more interest than a traditional savings account, depending on current rates.
  • Interest rates change over time, so an account offering 4.5% today may offer 3.5% in six months if the Federal Reserve cuts rates.

How daily compounding works

Most online savings accounts compound interest daily. This means the bank calculates how much interest you've earned that day, adds it to your balance, and then uses that new balance to calculate tomorrow's interest. The effect is small day-to-day but meaningful over months and years.

Here's a concrete example: if you have $10,000 in an account earning 4.5% APY, the bank divides 4.5% by 365 days to get a daily rate of about 0.0123%. On day one, you earn roughly $1.23. On day two, you earn interest on $10,001.23, not just the original $10,000—so you earn slightly more than $1.23. By the end of a year, compounding adds up to a noticeable difference compared to simple interest.

The difference between daily compounding and monthly compounding is small—usually less than $5 per year on a $10,000 balance—but it still favors daily compounding. Some banks compound quarterly or even annually, which means you earn less. Always check the account disclosure to see how often your bank compounds.

Why APY matters more than the interest rate

Banks sometimes advertise an "interest rate" separate from APY. The interest rate is the raw percentage; the APY includes the effect of compounding. Because of this, APY is always equal to or higher than the interest rate, and it's the only number you should use when comparing accounts.

If one bank advertises 4.48% interest compounded daily and another advertises 4.5% APY, they're roughly the same—the first bank's daily compounding gets it close to 4.5% APY. But if a bank advertises 4.5% interest compounded annually, its actual APY is lower, and you'll earn less money. The APY label removes the guesswork.

When you see an account advertised as "4.5% APY," that's the real number. You don't have to do any math or account for compounding. That's the rate you'll actually earn, assuming the rate doesn't change.

What happens when interest rates fall

Banks set their APY based partly on what the Federal Reserve does with its benchmark interest rate. When the Fed raises rates, banks compete to attract deposits and often raise their APY. When the Fed cuts rates, banks lower their APY because they can afford to pay less and still keep customers.

Your existing balance doesn't lose money when rates fall—you keep everything you've already earned. But new interest accrues at the lower rate going forward. If you opened an account at 5.0% APY six months ago and the rate drops to 3.5% APY today, your $10,000 still has the interest you already earned, but tomorrow's interest will be calculated at 3.5%, not 5.0%.

This is why some people move money between accounts when rates change. If your current bank drops its rate to 0.5% APY and another bank is offering 4.0% APY, moving your balance to the new bank means earning 3.5% more per year on that money going forward. There's no penalty for moving savings between banks.

How to calculate interest yourself

The formula for annual interest earned is: Balance × APY = Annual Interest. If you have $25,000 at 4.5% APY, you earn $25,000 × 0.045 = $1,125 per year, or about $94 per month.

For a specific number of days, divide the annual interest by 365 and multiply by the number of days. If you want to know how much you'll earn in 90 days on that same $25,000 at 4.5%, the math is: ($25,000 × 0.045) ÷ 365 × 90 = $278.77.

Keep in mind this assumes your balance stays constant. If you deposit more money or withdraw some, the interest calculation changes for the days after the deposit or withdrawal. Most banks show you the interest earned in your monthly statement, so you can verify the math without doing it yourself.

The difference between savings accounts and money market accounts

Money market accounts are a hybrid between a savings account and a checking account. They usually offer a higher APY than regular savings accounts but come with limits on how many withdrawals you can make per month. Both savings accounts and money market accounts are FDIC-insured up to $250,000 per depositor, per bank.

The interest calculation is identical—APY, daily compounding, the same formula. The difference is in how you access the money. A savings account lets you withdraw whenever you want. A money market account may limit you to six withdrawals per month, though many banks have relaxed this rule in recent years. If you need frequent access to your money, a savings account is simpler. If you're parking money for several months and want a slightly higher rate, a money market account might pay a bit more.

Interest earned versus interest paid

Interest earned in a savings account is taxable income. At the end of each year, your bank sends you a 1099-INT form showing how much interest you earned. You report this on your tax return, and you owe federal income tax on it (and state income tax in most states). This is different from interest you pay on a loan or credit card, which may be tax-deductible in some cases.

If you earned $500 in savings account interest and you're in the 22% federal tax bracket, you'll owe roughly $110 in federal tax on that interest. This is why the real return on your savings is slightly lower than the APY suggests—the APY is the gross return before taxes. Some people use tax-advantaged accounts like IRAs to hold savings and avoid this tax, though those accounts have contribution limits and withdrawal restrictions.

Frequently Asked Questions

How often do I see the interest posted to my account?

Most banks post interest monthly, though some post it daily or quarterly. Even if it's posted monthly, the interest is compounding daily behind the scenes. Check your account statement or the bank's website to see when interest posts. The timing doesn't affect how much you earn—only the APY and your balance matter.

Can I lose money in a savings account?

No. Your balance can only stay the same or go up (as interest accrues) or go down (if you withdraw money). The interest rate can fall, which means you earn less going forward, but you never lose the principal or the interest you've already earned. Savings accounts are FDIC-insured, so even if the bank fails, your money up to $250,000 is protected.

What's the difference between APY and APR?

APY (annual percentage yield) is used for savings and money market accounts—it includes the effect of compounding. APR (annual percentage rate) is used for loans and credit cards—it does not include compounding in the same way. When comparing savings accounts, always use APY. When comparing loans, always use APR.

Do I need a minimum balance to earn interest?

Some banks require a minimum balance to earn the advertised APY; others don't. If you fall below the minimum, the bank may pay a lower rate or charge a monthly fee. Read the account disclosure before opening an account. Many online banks have no minimum balance requirement.

What happens to my interest if I withdraw money mid-month?

Interest accrues daily, so you earn interest on your balance for each day you hold the money. If you withdraw $5,000 on the 15th of the month, you've already earned interest on that $5,000 for the first 14 days. You don't lose that interest. Going forward, the interest is calculated on your new, lower balance.