The basic idea: your bank pays you to let them use your money

When you put money in a savings account, the bank borrows it from you. In exchange, they pay you interest — a percentage of your balance, calculated and added to your account on a schedule the bank sets. The interest rate tells you what percentage of your balance you'll earn over a year. A 4% interest rate means that if you keep $1,000 in the account for a full year with no deposits or withdrawals, you'll earn $40.

The bank uses your money to lend to other customers or invest it. They keep the difference between what they pay you and what they earn. That's how they make money on savings accounts — and why different banks offer different rates. A bank with lower costs can afford to pay you more.

Interest rates change constantly. Banks raise them when the Federal Reserve raises its rates, and lower them when the Fed cuts. You might see rates advertised as 4.5% one month and 3.8% the next. The rate you see advertised is the rate new customers get when they open an account that day — your existing account may earn a different rate, and that rate can change too.

Key Takeaways

  • Interest is calculated as a percentage of your account balance, and the rate changes based on what the Federal Reserve does and what each bank decides to pay.
  • Banks compound interest, meaning you earn interest on the interest you've already earned, and how often they compound (daily, monthly, or yearly) affects your total earnings.
  • The APY (Annual Percentage Yield) is the rate that accounts for compounding, so it's always equal to or higher than the stated interest rate and is the number to compare between banks.
  • Your balance, how long you keep the money in the account, and the compounding frequency all change how much interest you actually earn.

How compounding turns your interest into more interest

Banks don't wait until the end of the year to pay you all your interest at once. Instead, they calculate interest on a schedule — daily, monthly, or quarterly — and add it to your account. Once that interest is added, the next calculation includes both your original balance and the interest you've already earned. This is called compounding, and it means you earn interest on your interest.

Here's a concrete example. Say you have $10,000 in an account earning 4% APY, and the bank compounds daily. On day one, the bank calculates one day's worth of interest (roughly $1.10) and adds it to your account. On day two, it calculates interest on $10,001.10, not just the original $10,000. By the end of the year, you'll have earned slightly more than $400 because of all that compounding.

The more often a bank compounds — daily is better than monthly, monthly is better than yearly — the more you earn. But the difference is usually small. A 4% APY account compounded daily versus monthly might earn you a few dollars more per year on $10,000. The bigger factor is the rate itself: a 4.5% account will always beat a 4% account, no matter how often either one compounds.

APY versus the stated interest rate: which number matters

Banks are required to show you two numbers: the interest rate and the APY (Annual Percentage Yield). The interest rate is the raw percentage. The APY is the rate after compounding is factored in — it's what you'll actually earn over a year if you don't touch the money.

The APY is always equal to or higher than the interest rate. If a bank shows you 4% interest and 4.05% APY, that 0.05% difference is the effect of compounding. When you're comparing savings accounts at different banks, always compare the APY numbers, not the interest rates. The APY is the true picture of what you'll earn.

Banks must display the APY prominently when they advertise rates, usually right next to the interest rate. If you see a rate advertised online or in a branch, the APY should be nearby. If it's not, ask for it before you open an account.

What changes how much interest you actually earn

Three things determine your real earnings: your balance, how long you keep the money in the account, and the compounding frequency. The balance is straightforward — $10,000 earns more than $1,000 at the same rate. Time matters too: if you withdraw money halfway through the year, you earn interest only on the balance for the time it was there. Some banks calculate interest daily and pay it monthly, so even a withdrawal on the last day of the month might cost you that month's interest.

The compounding frequency is the third piece. A bank that compounds daily will pay you slightly more than one that compounds monthly, all else equal. But this difference shrinks as rates get lower. At 0.5% APY, daily versus monthly compounding might earn you 50 cents more per year on $10,000. At 5% APY, it might earn you $2 more. The rate itself is always the dominant factor.

Some banks also offer promotional rates — higher rates for a limited time, usually for new customers or new deposits. These rates are real, but they often drop after a few months. Read the fine print to see when the promotional period ends and what your rate will be after that.

Why rates are different at different banks

Banks set their own rates based on their costs and their strategy. A bank with low overhead — few branches, mostly online — can afford to pay higher rates because they spend less money to run. A bank with many physical locations and more staff has higher costs and often pays lower rates to offset them.

Banks also compete for deposits. When one bank raises its rate to attract customers, others may follow. When the Federal Reserve cuts rates, banks usually cut theirs too, but not always at the same speed or by the same amount. This is why you'll see a range of rates across banks — some paying 4.5% while others pay 3.8% on the same type of account.

The type of account also matters. A regular savings account usually earns less than a money market account or a certificate of deposit (CD), because you can withdraw from savings anytime. Accounts with restrictions on withdrawals or that require you to keep money there for a set time often pay more, because the bank knows it can use that money for longer.

How to find the rate that's right for your situation

Start by checking what your current bank is paying. Log into your account online or call and ask for the APY on your savings account. Write it down. Then visit a few other banks' websites — both online banks and traditional banks with branches — and note their APYs. You're looking for the highest APY, but also consider whether you need a physical branch nearby or whether online-only banking works for you.

Pay attention to minimum balance requirements. Some banks pay high rates only if you keep a certain amount in the account — $25,000 or more, for example. If you can't meet that minimum, you'll earn a lower rate. Read the terms carefully before you open an account.

Remember that rates change. The rate you see today might be lower next month, or higher. If you find a bank paying significantly more than others, it's worth moving your money there — but don't chase rates constantly. Moving money between banks takes time and can be a hassle. A rate that's 0.1% higher isn't worth switching for, but 0.5% or more might be.

What happens to your interest if you withdraw money early

Savings accounts have no penalty for withdrawals, so you can take your money out anytime without losing the interest you've already earned. However, some banks calculate interest daily but pay it only at the end of each month. If you withdraw on the 15th of the month, you might not earn interest for the second half of the month, depending on the bank's rules.

Certificates of Deposit (CDs) are different. If you withdraw before the CD matures — before the set time period ends — you'll pay an early withdrawal penalty, which is usually a certain number of months' worth of interest. A CD might pay 5% APY but charge you three months of interest if you withdraw early. That penalty comes out of your earnings, not your original deposit.

Money market accounts fall somewhere in between. They usually allow a few withdrawals per month without penalty, but charge a fee if you exceed that limit. Check the account terms before you open one.

Frequently Asked Questions

Does the interest rate change after I open an account?

Yes. Banks can change the rate on savings accounts anytime, usually with a few days' notice. When the Federal Reserve changes its rates, banks typically adjust theirs within days or weeks. Your rate might go up or down depending on what the bank decides. CDs are different — once you open one, your rate is locked in for the full term.

Why does my bank show me two different numbers — interest rate and APY?

The interest rate is the base percentage the bank pays. The APY includes the effect of compounding — earning interest on your interest. The APY is always equal to or slightly higher than the interest rate, and it's the number that tells you what you'll actually earn over a year. Always compare APYs when choosing between accounts.

If I move my money to a different bank, do I lose the interest I've already earned?

No. The interest you've already earned is yours to keep. When you transfer money to a new bank, you take that balance with you. You'll start earning interest at the new bank's rate on that full amount. The only time you lose interest is if you withdraw early from a CD and pay the early withdrawal penalty.

How much money do I need to earn decent interest?

You earn interest on any balance, even $100. But the amount you earn depends on the rate and the balance. At 4% APY, $100 earns $4 per year. $10,000 earns $400 per year. There's no minimum to start earning, but larger balances earn noticeably more. Some banks do require a minimum balance to get their highest advertised rate.

Is it better to put money in a savings account or a CD?

Savings accounts let you withdraw anytime with no penalty, but usually pay lower rates. CDs lock your money away for a set time (three months to five years, typically) but usually pay higher rates. If you might need the money soon, a savings account is better. If you won't touch it for a year or more, a CD often pays more and might be worth the restriction.