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 lines of credit. The bank keeps the difference between what it pays you and what it charges borrowers. The amount the bank pays you is called interest, and it's expressed as a yearly percentage of your balance called the annual percentage yield, or APY.

The bank doesn't wait until the end of the year to calculate what you've earned. Instead, it calculates interest daily based on your balance that day, then adds it to your account monthly, quarterly, or annually depending on the account terms. The more money you keep in the account and the higher the APY, the more interest you earn.

Key Takeaways

  • Interest is calculated daily on your account balance, but credited (added to your account) on a schedule set by your bank—usually monthly or quarterly.
  • APY is the yearly interest rate; a higher APY means more money earned, and rates vary widely between banks and change over time.
  • Compound interest means you earn interest on your interest, which accelerates growth the longer money sits in the account.
  • The actual dollar amount you earn depends on three things: your balance, the APY, and how long the money stays in the account.

How daily interest calculation works

Banks use a method called daily compounding to calculate most savings account interest. Each day, the bank takes your current balance, divides the APY by 365, and multiplies that daily rate by your balance. That's the interest you earn that single day. The next day, the calculation includes the previous day's interest, so you earn interest on interest.

For example, if your account has an APY of 4.50% and a balance of $10,000, the daily rate is roughly 0.0123% (4.50% ÷ 365). On day one, you earn about $1.23. On day two, the bank calculates interest on $10,001.23, so you earn slightly more. This compounding effect is small day-to-day but adds up significantly over months and years.

The interest accrues (builds up) daily, but your bank doesn't add it to your balance immediately. Instead, banks hold the accrued interest and credit it on a set schedule—usually the last day of each month, the last day of each quarter, or the last day of the year.

When interest actually hits your account

The date your interest is credited matters because it determines when you can spend or move that money. Most banks credit interest monthly, meaning on the last business day of each month, all the interest you've earned that month appears in your account. Some banks credit quarterly (every three months) or annually (once a year).

Check your account agreement or call your bank to find out the crediting schedule. If you're comparing two accounts with similar APYs, monthly crediting is better than quarterly because you get access to your interest earnings sooner, and that interest can itself start earning interest in the next month.

If you withdraw money before the crediting date, you don't lose the interest you've already earned—it's still accruing daily. But if you close the account before interest is credited, some banks will not pay you the accrued interest. Read the fine print or ask before closing an account.

APY varies between banks and changes over time

Banks set their own APY rates based on what the Federal Reserve charges them to borrow money. When the Fed raises rates, banks gradually raise the APY they offer on savings accounts. When the Fed lowers rates, banks lower APY. The timing and amount of change is up to each bank—some move quickly, others lag behind.

APY also varies dramatically between banks. A large national bank might offer 0.01% APY on a basic savings account, while an online bank might offer 4.50% or higher on the same type of account. The difference comes down to operating costs: online banks have lower overhead, so they pass some of that savings to customers through higher rates.

If you opened a savings account years ago and haven't checked the rate recently, it's worth comparing. Your current bank's APY may have dropped significantly, and moving your money to a higher-rate account could earn you hundreds of dollars more per year on the same balance.

How to calculate what you'll actually earn

The formula for interest earned is: (Balance × APY ÷ 365) × Number of Days. If you keep $5,000 in an account with a 4.00% APY for 30 days, you earn roughly $16.44. Over a full year, that same $5,000 earns about $200.

Most banks provide an interest calculator on their website where you can enter your balance, the APY, and how long you plan to keep the money. The calculator shows you the projected earnings. Keep in mind that if the APY changes during your holding period, your actual earnings will differ from the projection.

The longer you leave money untouched in a savings account, the more compound interest works in your favor. A $10,000 deposit at 4.50% APY earns about $450 in the first year, but over five years it earns roughly $2,460 total—not just $2,250—because each year's interest starts earning interest too.

Why some accounts earn more than others

High-yield savings accounts offer significantly higher APY than traditional savings accounts at the same bank. The trade-off is usually that high-yield accounts require a higher opening balance (sometimes $2,500 or more) or have limits on how many withdrawals you can make per month.

Money market accounts and certificates of deposit (CDs) are other options. Money market accounts often pay higher interest than savings accounts but may require a larger minimum balance. CDs lock your money away for a set term (three months to five years) in exchange for a may provide APY that's usually higher than savings accounts. If you withdraw early, you pay a penalty.

Interest-bearing checking accounts exist but typically pay very low APY—often less than 0.10%—because banks use checking account deposits differently than savings deposits. If you want to earn meaningful interest, a dedicated savings account is the better choice.

What happens to interest if you move or withdraw money

Interest accrues daily, so if you withdraw $2,000 midway through the month, you still earn interest on the full balance up to that day. The interest you've already accrued stays in your account unless you withdraw it too. Only future interest is calculated on the lower balance.

If you transfer money to another bank, the interest you've earned up to that point remains in your original account. You don't lose it by moving banks. However, if you close the account before the next crediting date, confirm with your bank that accrued interest will be paid out—some banks pay it automatically, others require you to request it.

Frequent deposits and withdrawals don't affect how interest is calculated, but they do affect the average balance. If you deposit $5,000 on day one and withdraw $4,000 on day 15, your average balance for the month is lower, so you earn less interest than if you'd kept the full $5,000 the entire month.

Frequently Asked Questions

Is the interest I earn on a savings account taxable?

Yes. Interest earned on savings accounts is considered income and must be reported on your federal tax return. Banks send you a 1099-INT form each January if you earned $10 or more in interest during the previous year. State income tax may also apply depending on where you live.

Can a bank lower my APY without warning?

Banks can change APY at any time, but they must notify you before the change takes effect. Check your account agreement for how much notice they must give—it's usually 30 days. You can close the account and move your money elsewhere if you disagree with the new rate.

What's the difference between APY and APR?

APY includes the effect of compound interest, while APR does not. For savings accounts, APY is the number that matters because it shows what you'll actually earn. APR is used for loans and credit cards to show what you'll actually pay.

Do I lose interest if I don't make deposits every month?

No. Interest is calculated on whatever balance sits in your account, whether you add money or not. You can deposit once and let the account grow through interest alone, or deposit regularly—either way, interest accrues on the full balance every day.

Why is my interest so low if the APY seems high?

The APY is a yearly rate. If your account shows 4.50% APY but you've only had money in it for one month, you earn roughly one-twelfth of that rate. Also, interest is calculated on your actual balance—if you had $1,000 in the account for half the month and $5,000 for the other half, your interest reflects that average balance.