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. In exchange, the bank pays you interest — a percentage of your balance that gets added to your account on a set schedule. The rate the bank offers you depends on the current market, the bank's own costs, and how much competition exists for deposits in your area.

The amount you earn depends on three things: how much money sits in the account, what interest rate the bank offers, and how often the bank calculates and adds interest to your balance. A higher rate means more money in your pocket. A longer time between interest payments means you earn less, because the bank is not adding interest to your interest as often.

Interest rates on savings accounts change. Banks raise them when the Federal Reserve raises its benchmark rate, and lower them when the Fed cuts rates. You might see a high rate advertised for new customers, then watch it drop after a few months. Read the fine print before opening an account, and check your rate periodically — if it falls too low, moving your money to a different bank can be worth the effort.

Key Takeaways

  • Banks pay you interest because they lend out your deposits to other customers and keep the difference between what they pay you and what they charge borrowers.
  • Your interest earnings depend on your account balance, the interest rate the bank offers, and how often interest is calculated — usually daily or monthly.
  • Interest rates fluctuate with the Federal Reserve's decisions and vary widely between banks, so comparing rates before opening an account matters.
  • Compound interest means the bank adds interest to your interest, so your balance grows faster the longer money sits untouched in the account.
  • Some accounts require a minimum balance to earn interest, and some charge fees that can wipe out your earnings if the balance is small.

How the bank calculates the interest you earn

Banks use a formula based on your balance, the annual interest rate, and the number of days interest accrues. Most savings accounts calculate interest daily but pay it out monthly. That means the bank looks at your balance at the end of each day, applies a tiny fraction of the annual rate, and keeps a running total. At the end of the month, it deposits the sum into your account.

The exact formula is: (Balance × Annual Rate) ÷ 365 days. If you have $10,000 in an account earning 4.5% annual interest, the daily interest is about $1.23. Over 30 days, that adds up to roughly $37. The bank will show you the exact amount when interest posts — check your statement or your online account to see what you actually earned that month.

Some banks calculate interest quarterly (every three months) or annually instead of monthly. The less often interest is calculated, the less you earn, because you miss out on compound interest — the interest that would have been paid on your previous interest. A monthly calculation beats a quarterly one, and daily beats monthly. When comparing accounts, look for the APY (annual percentage yield), which already factors in how often interest is compounded, so you can compare apples to apples.

Compound interest: earning money on your earnings

Once the bank adds interest to your account, that interest becomes part of your balance. The next time interest is calculated, you earn interest on the original balance plus the interest you already earned. This is compound interest, and it is the reason leaving money untouched in a savings account makes it grow faster over time.

The longer your money stays in the account, the more noticeable compound interest becomes. After one month at 4.5% APY on $10,000, you have about $10,037. After one year, you have roughly $10,460. After five years, you have about $12,461. The difference between one year and five years is not just five times the first year's earnings — it is more, because each year you are earning interest on a larger balance.

This is why moving money in and out of the account hurts your earnings. If you withdraw $5,000 after six months, you lose not only the interest that $5,000 would have earned in the second half of the year, but also the compound interest on that interest. Savings accounts work best when you can leave the money alone.

Minimum balances and fees that reduce your interest

Many banks require a minimum balance to earn interest at all. Common minimums are $500, $1,000, or $2,500. If your balance falls below the minimum, the bank stops paying interest until you bring it back up. Some accounts have tiered rates — a higher rate if your balance is above a certain threshold, a lower rate below it.

Monthly maintenance fees are another way your earnings shrink. A $5 or $10 monthly fee on a small account earning $2 to $3 per month wipes out your interest entirely. Before opening an account, find out whether the bank charges a monthly fee, whether the fee is waived if you maintain a minimum balance or set up direct deposit, and whether the fee applies to all account types or only certain ones.

Some banks offer no-fee accounts with no minimum balance but pay a lower interest rate. Others pay a higher rate but charge a fee or require a large minimum. The math is simple: calculate what you would earn in a year at each bank, subtract any fees, and compare the net result. A 4% rate with no fees often beats a 4.5% rate with a $10 monthly fee, depending on your balance.

Why interest rates vary so much between banks

Online banks typically offer higher interest rates than brick-and-mortar banks because they have lower overhead costs — no physical branches, fewer employees, cheaper rent. They pass those savings to customers in the form of higher rates. A traditional bank might offer 0.01% APY while an online bank offers 4.5% APY on the same type of account.

Credit unions, which are member-owned rather than shareholder-owned, sometimes offer competitive rates as well. You have to be a member to open an account, but membership is often free or costs a small one-time fee. Credit unions are insured by the NCUA (National Credit Union Administration) the same way banks are insured by the FDIC, so your money is equally safe.

Rates also depend on the Federal Reserve's current policy. When the Fed raises its benchmark interest rate, banks raise savings account rates to attract deposits. When the Fed cuts rates, banks cut savings rates quickly — sometimes within days. This is why a high rate you see advertised today might be much lower in six months. Lock in a good rate while you can, but understand that it will not last forever.

How to track your interest earnings and spot problems

Check your account statement or online banking portal every month when interest posts. The statement will show the interest amount, the date it was added, and your new balance. Over time, you can see whether the interest matches what you expected based on the advertised rate.

If the interest seems low, calculate it yourself. Multiply your average balance by the APY and divide by 12 (for monthly interest). If your calculation is significantly higher than what the bank paid, contact the bank and ask why. Common reasons include a rate cut you were not notified about, a balance that fell below the minimum at some point during the month, or a fee you did not know about.

If you notice the bank lowered your rate without warning, you have options. Some banks notify customers by email or mail, but not all do. If the rate drop is steep, moving your money to a different bank might make sense. Online banks make this easy — you can open a new account and transfer funds in a few days.

Interest on money you withdraw before the end of the month

Most banks calculate interest based on your daily balance, so if you withdraw money partway through the month, you earn interest only on the balance for the days the money was in the account. If you had $10,000 for the first 15 days of the month and $5,000 for the last 15 days, the bank calculates interest on both balances separately and adds them together.

Some older accounts use the "average daily balance" method, which adds up your balance for each day of the month and divides by the number of days. This method is less common now, but it works the same way — you earn interest only on money that was actually in the account.

A few accounts use the "low balance" method, where the bank pays interest only on the lowest balance you held during the month. This is rare and unfavorable to customers, so avoid accounts that use this method if you can. Always ask the bank which method they use before opening an account.

Frequently Asked Questions

Can I lose money in a savings account if interest rates drop?

No. Your balance itself never decreases because of interest rate changes. If rates drop, you simply earn less interest going forward — the money you already have stays in the account. The only way to lose money is if the bank charges fees that exceed your interest earnings, or if you withdraw funds and the bank penalizes early withdrawal (which is rare for savings accounts).

Is the interest rate the same as the APY?

No. The interest rate is the annual percentage the bank offers. The APY (annual percentage yield) is the actual return you get after accounting for how often interest is compounded. APY is always equal to or higher than the interest rate. When comparing accounts, always compare APY to APY, not rate to rate.

What happens to my interest if I close the account mid-month?

You receive interest for the days your money was in the account up to the close date. The bank calculates a pro-rated amount based on your daily balance and adds it before closing the account. You will see this interest on your final statement or receive it as a check, depending on the bank's policy.

Does the FDIC insurance cover my interest earnings?

Yes. FDIC insurance covers your account balance plus accrued interest up to $250,000 per depositor per bank. Interest that has been added to your account counts toward that limit. If you have $249,000 and earn $2,000 in interest, the total of $251,000 is covered up to the $250,000 limit, so $1,000 would not be insured — but this only matters if the bank fails.

Should I move my money to a different bank if rates drop?

It depends on how much money you have and how much the rate dropped. Moving $5,000 from a 4.5% account to a 3.5% account costs you about $50 per year — probably not worth the effort. Moving $100,000 costs you $1,000 per year, which is worth investigating. Factor in any fees or minimum balance requirements at the new bank before deciding.