What you earn depends on the bank's rate, how much you deposit, and how long the money sits there

The amount of interest you earn is calculated by multiplying your account balance by the annual percentage yield (APY) the bank offers, then dividing by 12 for each month the money stays in the account. A $10,000 deposit in an account with a 4.5% APY earns roughly $450 per year, or about $37.50 per month. But that number changes if the bank lowers its rate, if you withdraw money, or if you add more deposits.

Banks set their own rates based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, banks typically raise savings rates within weeks. When the Fed cuts rates, banks cut savings rates much faster—sometimes within days. This means the rate you see today may not be the rate you earn six months from now.

The actual dollars you receive depend on three things: the APY offered, your balance, and the time period. Online banks and credit unions often pay 4% to 5.35% APY right now, while traditional brick-and-mortar banks often pay 0.01% to 0.5%. The difference between those two is enormous over time.

Key Takeaways

  • Interest earned equals your balance multiplied by the APY, divided by 12 for monthly earnings—a $5,000 balance at 4.5% APY earns about $18.75 per month.
  • Banks change their rates whenever they choose, and online banks typically pay two to ten times more than traditional banks for the same deposit.
  • Interest compounds monthly at most banks, meaning you earn interest on the interest you already earned, but the effect is small in savings accounts.
  • Withdrawals reduce your balance immediately, so taking money out mid-month lowers that month's interest payout.
  • The rate you see advertised is only may provide for new deposits; your existing balance may earn a different rate if the bank changes it.

How the math works with real numbers

Start with the formula: Balance × APY ÷ 12 = Monthly Interest. If you have $20,000 in an account paying 4.5% APY, you earn $20,000 × 0.045 ÷ 12 = $75 per month. After 12 months, you have $20,900 (the original $20,000 plus $900 in interest).

If that same $20,000 sits in a traditional bank account paying 0.05% APY, you earn $20,000 × 0.0005 ÷ 12 = $0.83 per month. After a year, you have $20,010. The difference between the two accounts is $890 per year on the same deposit—that is money you leave on the table by choosing the wrong bank.

The math gets slightly more complex if the bank compounds interest daily instead of monthly. Most online banks compound daily, which means they calculate interest on your balance every single day and add it to your account. The effect is small—on a $20,000 balance at 4.5% APY, daily compounding earns you about $2 more per year than monthly compounding. It is real money, but not transformative.

Why your rate can change and when banks notify you

Banks are not required to lock in a rate for any length of time on savings accounts. They can lower your rate whenever they want, and most do not need to give you advance notice—they just change it. Some banks notify you by email or through your online portal; others post the change on their website. You should check your account terms or call your bank to understand their notification policy.

Rate cuts usually happen when the Federal Reserve cuts its benchmark rate. The Fed does not control bank rates directly, but banks follow the Fed's moves closely because it affects what they pay to borrow money. When the Fed raises rates, banks raise savings rates to attract deposits. When the Fed cuts rates, banks cut savings rates to protect their profit margins.

The advertised rate you see on a bank's website is typically only may provide for new money you deposit. Your existing balance may earn a different rate, especially if you opened the account years ago. Read your account agreement or contact the bank to find out what rate applies to your current balance.

How deposits and withdrawals affect your monthly earnings

Banks calculate interest based on your balance on specific days of the month, not your average balance. Most use the "daily balance method," which means they look at what you have in the account each day and calculate interest on that. If you deposit $5,000 on the 15th of the month, you earn interest on that $5,000 for only the remaining days of that month—roughly half a month's worth.

Withdrawals work the same way. If you withdraw $10,000 on the 10th, you stop earning interest on that $10,000 for the rest of the month. This is why timing matters if you are moving money between accounts. Withdraw on the last day of the month and you lose almost a full month of interest on that amount.

Some banks offer a grace period where they do not penalize you for withdrawals, but savings accounts are not designed for frequent movement of money. If you need to access your money regularly, a money market account or checking account may be more practical, though they typically pay lower interest.

The difference between advertised rate and what you actually earn

Banks advertise APY, which includes the effect of compounding. This is the number you should use to calculate your actual earnings. Some older accounts or promotional rates may be quoted as APR (annual percentage rate) instead, which does not include compounding and will understate what you actually earn.

The advertised rate is also usually the rate for new deposits. If you have an older account, your rate may be lower. Some banks grandfather existing customers at old rates and offer new customers higher rates. You can ask your bank what rate applies to your specific account balance, or you can switch to a bank that pays the same rate to all customers.

Banks also sometimes offer promotional rates that are higher than their standard rate, but only for a limited time or only on new deposits. Read the fine print to see when the promotional rate expires and what your rate will be after that.

Comparing what different account types pay

High-yield savings accounts at online banks currently pay between 4% and 5.35% APY, depending on the bank and the current rate environment. Traditional banks pay 0.01% to 0.5%. Credit unions often pay rates similar to online banks, sometimes higher. Money market accounts pay rates similar to savings accounts but may require a higher minimum balance.

Certificates of deposit (CDs) lock your money in for a set period—three months, six months, one year, five years—and pay a fixed rate for that entire period. CD rates are usually higher than savings account rates because the bank knows it can use your money for longer. A one-year CD might pay 5.25% while a savings account pays 4.75%, but you cannot touch the money without paying a penalty.

The tradeoff is flexibility versus rate. Savings accounts let you withdraw anytime without penalty but pay lower rates. CDs pay higher rates but lock your money away. If you need the money within a year, a savings account is the right choice even if the rate is lower.

What happens to your interest if rates drop

If your bank lowers its rate, your monthly earnings drop immediately. If you were earning $75 per month at 4.5% APY and the bank cuts the rate to 3.5% APY, you now earn about $58 per month on the same $20,000 balance. That is $17 less per month, or $204 less per year.

You have no contractual right to keep the old rate. The bank can change it anytime. Your only recourse is to move your money to a bank that pays a higher rate. This is why it makes sense to shop around every few months, especially when the Fed is cutting rates. A rate drop at your current bank is a signal to check what competitors are offering.

Some banks do raise rates on existing balances when the Fed raises rates, but they cut rates on existing balances faster than they raise them. This is normal banking practice. If you want to protect yourself, move your money to a bank with a strong track record of raising rates quickly when the Fed moves.

Frequently Asked Questions

How often does interest get added to my account?

Most banks add interest monthly, though some add it daily or quarterly. Check your account agreement or call your bank to find out. Even if interest is calculated daily, it is usually deposited once a month. The frequency does not change the total amount you earn per year, only how often you see the deposit.

Can I lose money in a savings account?

No. Your balance cannot go down due to interest rates or market changes. The only way your balance decreases is if you withdraw money or the bank charges a fee. Savings accounts are FDIC-insured up to $250,000 per depositor per bank, so your money is protected even if the bank fails.

What is the difference between APY and APR?

APY includes the effect of compounding interest over a year, while APR does not. APY is always higher than APR on the same rate. Banks advertise APY for savings accounts because it shows the true annual return. Always use APY when comparing savings accounts.

Should I move my money if my bank lowers the rate?

It depends on how much lower. If your bank drops from 4.5% to 4.4%, the difference is small. If it drops from 4.5% to 2%, moving your money to a bank paying 4.5% saves you significant money. Calculate the annual difference and decide if it is worth the time to switch.

Do I have to pay taxes on savings account interest?

Yes. Interest earned in a savings account is taxable income. Your bank will send you a 1099-INT form at the end of the year if you earned $10 or more in interest. You report this on your tax return. The amount you owe in taxes depends on your tax bracket.