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

When you put money in a savings account, the bank lends that money to other customers—for mortgages, car loans, business lines of credit. The bank keeps the difference between what it pays you and what it charges borrowers. That payment to you is interest.

The amount you earn depends on three things: how much you have in the account, how long it stays there, and the interest rate the bank offers. The rate is expressed as an annual percentage—for example, 4.5% per year. The bank calculates what you owe based on that percentage, then deposits the earnings into your account on a schedule (usually monthly or daily).

The rate your bank offers changes based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, banks typically raise the rates they offer on savings accounts. When the Fed cuts rates, savings rates fall. This is why the interest you earn can be higher at some times than others, even at the same bank.

Key Takeaways

  • Interest is calculated as a percentage of your account balance, and the rate varies by bank and changes when the Federal Reserve adjusts its benchmark rate.
  • Most banks compound interest daily or monthly, meaning you earn interest on your interest, and the compounding schedule affects your total earnings.
  • A higher APY (annual percentage yield) accounts for compounding, while APR (annual percentage rate) does not, so compare APY when choosing between accounts.
  • You see interest deposits in your account on a regular schedule—usually monthly—though the bank calculates it more frequently behind the scenes.
  • Moving money out of the account or closing it stops interest from accruing on that balance, so timing matters if you are planning a withdrawal.

How the bank calculates interest: the formula and the timeline

The basic formula is straightforward: Interest = Balance × Rate ÷ 365 × Days. If you have $10,000 in an account earning 4.5% annual interest, and the bank calculates interest daily, you earn about $1.23 per day ($10,000 × 0.045 ÷ 365). Over a month, that adds up to roughly $37.

Most banks calculate interest daily but compound it—meaning they add earned interest back into your balance, and then calculate interest on that larger amount the next day. This is why the same rate earns you slightly more money than straightforward math suggests. The difference is small on a savings account, but it compounds over time.

The bank does not pay you daily, though. Instead, it posts the accumulated interest to your account on a set schedule. Most banks post monthly, though some post quarterly or even annually. When you log in and see your balance go up, that is the posted interest hitting your account. Between postings, the interest is accruing—building up—but you cannot spend it yet.

APY versus APR: why the label matters when comparing rates

APY (annual percentage yield) is the rate that includes compounding. It tells you the actual amount you will earn in a year if you leave the money untouched. APR (annual percentage rate) does not include compounding—it is the raw rate before the bank adds interest back into the balance.

When you are comparing savings accounts, always look at the APY, not the APR. A bank might advertise a 4.5% APR, but if it compounds daily, the actual APY might be 4.60%. That difference sounds small, but on $50,000 it means an extra $50 per year. On larger balances or longer time periods, the gap widens.

Banks are required to display APY prominently in their account disclosures and on their websites, so you can compare directly. If a bank only shows APR, that is a sign to look elsewhere or ask them to clarify the APY.

What happens to interest when you withdraw money or close the account

Interest accrues only on the balance that stays in the account. If you have $10,000 earning 4.5% and you withdraw $5,000 midway through the month, the bank calculates interest on the full $10,000 for the days it was there, then on $5,000 for the remaining days. You do not lose the interest you already earned, but you stop earning interest on the withdrawn amount.

If you close the account, the bank stops calculating interest when ready. Any accrued but unposted interest—money that has been earned but not yet added to your balance—is usually paid out when the account closes. Check your account closure confirmation to see the final interest payment.

Some savings accounts have minimum balance requirements. If your balance drops below the minimum, the bank may stop paying interest or charge a monthly fee. Read your account agreement to know the threshold and whether it applies to you.

Why rates change and how to track what your bank is offering

Banks set their savings rates based on the Federal Funds Rate, which the Federal Reserve adjusts roughly eight times per year. When the Fed raises its rate, banks raise savings rates within days or weeks. When the Fed cuts, banks cut savings rates—sometimes faster than they raised them.

Your bank does not have to match every Fed move exactly. Some banks raise rates quickly to attract deposits; others move slowly. Some banks cut rates quickly when the Fed cuts; others hold rates steady longer. This is why the same Fed rate can mean 4.5% at one bank and 3.8% at another.

You can track Fed rate changes through the Federal Reserve's website or financial news outlets. If your bank's rate lags significantly behind competitors, you have the option to move your money to a higher-paying account. There is no penalty for moving savings between banks—you straightforward withdraw from one and deposit into another.

How interest compounds over time and why it matters for long-term savings

Compounding means you earn interest on your interest. In month one, you earn interest on your original balance. In month two, you earn interest on the original balance plus the month-one interest. In month three, you earn on all three amounts. The longer the money sits, the more noticeable the effect becomes.

On a $10,000 balance at 4.5% APY compounded daily, after one year you have $10,460. After five years, you have $12,461. After ten years, you have $15,530. The difference between year one and year ten is not linear—the later years earn more because the base is larger. This is why starting early, even with a small balance, matters for long-term savings.

The effect is stronger with higher rates and longer time periods. At 1% APY, the same $10,000 grows to $10,100 in one year and $10,512 in five years. At 5% APY, it grows to $10,513 in one year and $12,763 in five years. The rate difference compounds too.

Where to find your interest earnings and what the statements show

Your bank statement lists interest deposits separately from other transactions. Look for a line item labeled "Interest Paid" or "Interest Earned" posted on the last day of each month (or whatever schedule your bank uses). The amount shown is the interest that accrued and posted during that period.

Online banking platforms usually show your current APY in the account details section. Some banks also show a year-to-date interest total, which tells you how much you have earned since January 1. If you cannot find this information, your bank's customer service can tell you your current rate and show you how much you have earned.

At tax time, the bank sends you a 1099-INT form if you earned $10 or more in interest during the year. You report this interest as income on your federal tax return. The threshold varies by state, so check your state's rules as well. Interest earned is taxable income, even though the amount is usually small on a savings account.

Frequently Asked Questions

Can I lose money if the interest rate drops?

No. The interest rate affects how much you earn going forward, not what you have already earned. If your rate drops from 4.5% to 3.8%, you keep all the interest you earned at the higher rate. You straightforward earn less on new interest calculations. Your principal balance never decreases because of a rate change.

Do I have to do anything to earn interest, or does it happen automatically?

It happens automatically. Once you open a savings account and deposit money, the bank begins calculating and posting interest on its schedule. You do not need to take any action. Interest accrues whether you check your account or not.

What is the difference between a savings account and a money market account for interest?

Money market accounts typically offer slightly higher rates than standard savings accounts, but they usually require a larger minimum balance and limit how many withdrawals you can make per month. Both earn interest the same way—daily calculation, regular posting. The rate difference depends on the bank and current market conditions.

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

No. When you close an account, the bank pays out all accrued interest, including any that has not yet posted. You receive that money along with your principal. You do not forfeit interest by switching banks.

Why does my bank show a different interest amount each month?

The amount varies because your balance may change month to month. If you deposit more money, the next month's interest is higher. If you withdraw, the next month's interest is lower. Also, months have different numbers of days, which affects the calculation slightly. These variations are normal.