Interest is money the bank pays you for letting them use your deposits

When you put money in a savings account, the bank lends that money to other customers through mortgages, car loans, and business credit lines. The bank keeps the difference between what it pays you and what it charges borrowers. That difference is how banks make money. The amount they pay you is called interest, and it's calculated as a percentage of your account balance.

The rate the bank offers you—called the annual percentage yield or APY—tells you exactly how much you'll earn in a year if your balance stays the same. A 4.5% APY means the bank will pay you 4.5% of your balance over twelve months. The actual dollar amount depends on how much you have saved and how long you leave it there.

Interest rates change constantly. Banks raise them when the Federal Reserve increases its benchmark rate, and they lower them when the Fed cuts rates. You might see a high rate advertised, but that rate is only may provide for the term stated—often just a few months. After that, the bank can lower it without asking your permission.

Key Takeaways

  • Banks pay you interest as a percentage of your balance, stated as an annual percentage yield (APY), which tells you what you'll earn in one year if your balance doesn't change.
  • Interest compounds—meaning you earn interest on your interest—and the frequency of compounding (daily, monthly, quarterly) affects how much total interest you receive.
  • The APY you see advertised is often a promotional rate that applies for a limited time, after which the bank can lower it without your consent.
  • You can compare rates across banks because they all use APY as the standard measure, making it easier to find accounts that pay more.

How compounding multiplies your interest over time

Interest doesn't just sit on top of your balance—it gets added to your account, and then you earn interest on that interest too. This is called compounding. If you have $1,000 at 4% APY compounded daily, the bank calculates your interest every single day, adds it to your account, and tomorrow you earn interest on the new, slightly larger balance.

The more often interest compounds, the more you earn. Daily compounding beats monthly compounding, which beats annual compounding, even at the same stated rate. Most savings accounts compound daily, which is why you should look for that detail when comparing banks. Some accounts compound monthly or quarterly, and those will pay you less over time.

The difference is small on modest balances but grows with larger amounts and longer time periods. On $10,000 at 4% APY, daily compounding might earn you about $408 in a year, while monthly compounding might earn you about $407. That one dollar doesn't sound like much, but over five years the gap widens to roughly $20.

Why the APY is more useful than the interest rate

Banks sometimes advertise an interest rate separate from the APY. The interest rate is the raw percentage, while the APY includes the effect of compounding. The APY is always the number you should use to compare accounts, because it shows you the real amount you'll earn.

For example, a bank might advertise 3.9% interest compounded daily. When you calculate what that actually pays you over a year with daily compounding, it comes out to 3.98% APY. The difference is small here, but some accounts compound less frequently, and the gap between the rate and the APY can be larger. Always look for the APY on the account disclosure—it's the number that matters for your decision.

When and how the bank deposits your interest

Banks don't pay interest all at once at the end of the year. Instead, they deposit it into your account on a schedule—usually monthly, sometimes quarterly. You'll see the deposit appear as a credit to your account, just like a transfer from another person would. Once it's in your account, it becomes part of your balance and starts earning interest itself.

The exact date the interest posts varies by bank. Some deposit on the first business day of the month, others on the last day of the month, and some on a date tied to when you opened the account. Check your account agreement or call the bank to find out when to expect your interest deposits. This matters if you're tracking your balance for a specific reason, like making sure you stay above a minimum.

How your balance affects what you earn

Interest is calculated on your average daily balance during the month (or quarter, depending on the bank). This means the bank adds up what you had in the account each day, divides by the number of days, and uses that average to calculate interest. If you had $1,000 for 20 days and $2,000 for 10 days in a month, your average daily balance would be about $1,333.

Some banks use the lowest balance during the period instead, which pays you less. Always check the account disclosure to see which method your bank uses. Most online banks and credit unions use average daily balance, which is fairer to you if your balance fluctuates.

Deposits and withdrawals change your balance when ready, so timing matters if you're trying to maximize interest. Depositing money early in the month gives it more days to earn interest that month. Withdrawing money late in the month means you keep the interest you've already earned but reduce what earns interest going forward.

Why rates are higher at online banks and credit unions

Online banks and credit unions typically offer higher APYs than large brick-and-mortar banks. This is because they have lower overhead costs—no physical branches, fewer employees, cheaper real estate. They pass those savings to customers through better rates. A large national bank might offer 0.01% APY while an online bank offers 4.5% APY on the same type of account.

The tradeoff is convenience. You can't walk into a branch to deposit cash or speak to someone in person. Most online banks let you deposit checks by phone camera and transfer money electronically, which works for most people. If you need in-person service, you'll pay for it in lower interest rates.

Credit unions are member-owned, not shareholder-owned, so they return profits to members through better rates and lower fees. You have to be a member to open an account, which usually means working for a specific employer, belonging to a certain organization, or living in a certain area. If you're may be able to access, credit unions are worth exploring for savings accounts.

What happens to your interest if rates drop

When the Federal Reserve lowers interest rates, banks lower the APY they offer on new deposits. If you already have money in a savings account, the rate on your existing balance will drop too—usually within a few weeks. The bank doesn't have to notify you in advance; they can change the rate on existing accounts as long as they follow the terms in your account agreement.

This is why high-yield savings accounts are temporary opportunities, not permanent solutions. A 4.5% rate today might be 2% in six months if the Fed cuts rates. You should move money to whichever bank is currently offering the best rate, knowing you may need to move it again later. Some people use a spreadsheet or check rate-tracking websites monthly to stay on top of which banks are paying the most.

Rate increases work the opposite way. When the Fed raises rates, banks raise the APY on new accounts first, and existing accounts follow more slowly. If you're in a low-rate account when rates are rising, you're losing money compared to what you could earn elsewhere. This is another reason to shop around periodically.

Frequently Asked Questions

Do I have to pay taxes on savings account interest?

Yes. Interest is taxable income. Banks send you a 1099-INT form each January if you earned $10 or more in interest during the year. You report this on your tax return. The amount of tax you owe depends on your total income and tax bracket. If you earned $100 in interest, you might owe $20 to $37 in federal tax, depending on your situation.

What's the difference between a savings account and a money market account?

Money market accounts usually pay slightly higher interest than savings accounts, but they often require a larger minimum balance and limit how many withdrawals you can make per month. Both are FDIC insured up to $250,000. If you need to access your money frequently, a regular savings account is simpler. If you have a large balance and won't touch it often, a money market account might pay more.

Can I lose money in a savings account?

No. Savings accounts are FDIC insured, meaning the federal government guarantees your deposits up to $250,000 per bank, per account type. You cannot lose your principal. However, if inflation is higher than your interest rate, your money loses purchasing power—it buys less stuff even though the dollar amount stays the same. This is why comparing rates matters.

How often should I move my money to get the best rate?

There's no penalty for moving money between banks, so you can switch whenever you find a better rate. Some people move money every few months, others once a year. The tradeoff is time and effort against earning an extra 0.5% or 1%. On $10,000, moving to a 1% higher rate earns you $100 more per year, which might be worth the 30 minutes of work to you.

What if my bank goes out of business?

Your deposits are protected by FDIC insurance up to $250,000 per account type at each bank. If a bank fails, the FDIC pays you directly, usually within a few business days. You don't lose money. This is why it's safe to use smaller online banks and credit unions—the insurance protection is the same as at large national banks.