The amount you earn depends on three things: how much you deposit, the APY the bank offers, and how long the money sits there

Your savings account interest comes from a straightforward formula: your balance multiplied by the annual percentage yield (APY), divided by 365 days. If you keep $10,000 in an account with a 4.5% APY for a full year, you earn roughly $450. If you keep it for six months, you earn roughly $225. The bank calculates and deposits this interest monthly or daily depending on the account, but the yearly math stays the same.

The catch is that APY rates change. Banks raise them when the Federal Reserve raises its benchmark rate, and lower them when the Fed cuts. A 4.5% APY today might be 3.8% in six months. Your earnings depend on the rate at the moment your money sits in the account, not the rate when you opened it.

The other variable is your balance itself. If you deposit $500 one month and $5,000 the next, the bank typically calculates interest on the average daily balance—what you actually held each day. Depositing money late in the month means less interest that month. Withdrawing money early means you lose interest on that amount for the rest of the period.

Key Takeaways

  • Interest earned equals your balance times the APY divided by 365, so a $10,000 deposit at 4.5% APY earns about $450 per year.
  • Banks calculate interest on your average daily balance, so the timing of deposits and withdrawals within a month affects how much you earn.
  • APY rates change when the Federal Reserve adjusts its benchmark rate, so the rate you see today may not be the rate next quarter.
  • High-yield savings accounts currently offer 4% to 5.35% APY, while traditional bank savings accounts often offer 0.01% to 0.05%.
  • Interest compounds daily or monthly depending on the account, meaning you earn small amounts of interest on your interest.

How banks calculate your monthly interest

Banks use one of two methods: average daily balance or daily balance. With average daily balance, the bank adds up what you held each day of the month and divides by the number of days. With daily balance, the bank calculates interest on each day's balance separately and adds them up. Daily balance usually earns you slightly more because interest compounds more frequently, but the difference is small on typical account sizes.

Most online banks and credit unions post interest monthly. Some post it daily but hold it until the end of the month. A few post it quarterly. The frequency matters only if you plan to withdraw the interest when ready—if you leave it in the account, it compounds either way, and you earn interest on the interest.

You will see the interest posted as a credit to your account. It shows up as a separate line item in your transaction history, labeled as "interest paid" or "interest earned." You do not have to do anything to receive it—the bank calculates and deposits it automatically.

Why the same deposit earns different amounts at different banks

A $50,000 deposit earns $2,250 per year at a 4.5% APY bank, but only $25 per year at a 0.05% APY bank. That $2,225 difference comes entirely from the APY rate the bank chose to offer. Banks set their own rates based on how much they need deposits, what they can earn by lending that money out, and how much they pay for other funding sources.

Online banks typically offer higher APY than brick-and-mortar banks because they have lower overhead costs. They do not maintain physical branches, so they pass some of that savings to depositors in the form of higher rates. A traditional bank might offer 0.01% APY while an online bank offers 4.75% APY on the same type of account.

Banks also offer different rates for different account types. Money market accounts sometimes pay slightly more than savings accounts. Certificates of deposit (CDs) lock your money away for a set term—three months, one year, five years—and pay a higher rate in exchange. Regular savings accounts are the most flexible but usually pay the least.

What happens when interest rates fall

When the Federal Reserve lowers its benchmark rate, banks lower their APY within days or weeks. A savings account paying 5.0% might drop to 4.5% within a month. Your balance does not change, but your monthly interest earnings shrink. A $100,000 balance earning $416 per month at 5.0% APY drops to $375 per month at 4.5% APY—a loss of $41 per month or $492 per year.

You cannot lock in a rate on a regular savings account. The bank can change it anytime without notice. If you want a may provide rate, you need a CD. A one-year CD at 4.8% APY will pay 4.8% for the full year even if rates fall to 2.0%. The tradeoff is that you cannot withdraw the money without a penalty—usually a loss of three to six months of interest.

Rates can also rise. When the Federal Reserve raises its benchmark rate, banks raise their APY to attract deposits. If you are in a savings account when rates rise, your earnings increase automatically. If you are in a CD, you are locked into the old rate and miss the increase.

How to compare what you will earn across banks

The only number that matters is APY, not interest rate. APY includes compounding, so it shows the true annual return. Two banks might advertise different interest rates but the same APY because one compounds daily and one compounds monthly. APY makes them comparable.

To estimate your earnings, multiply your balance by the APY and divide by 12 for a monthly estimate. A $25,000 balance at 4.5% APY earns roughly $93.75 per month. A $25,000 balance at 0.05% APY earns roughly $1.04 per month. The difference is $92.71 per month or $1,112 per year—real money worth shopping for.

Check the APY on the bank's website or call and ask. APY changes frequently, so a rate you saw last week may have shifted. Some banks list APY prominently; others bury it. Look for the annual percentage yield label, not just "interest rate." If a bank does not clearly state the APY, move on—transparency matters.

The role of your account balance and deposit timing

Interest earnings scale directly with balance. Double your balance and you double your interest. A $5,000 balance at 4.5% APY earns $225 per year. A $10,000 balance at the same rate earns $450 per year. This is why moving money from a checking account (which earns little or no interest) to a savings account (which earns 4% or more) can add hundreds of dollars per year to your earnings.

The timing of deposits within a month affects that month's interest. If you deposit $10,000 on the first of the month, it earns interest for the full 30 days. If you deposit it on the 30th, it earns interest for only one day. Banks calculate based on average daily balance, so early deposits earn more that month. This matters most if you are moving large sums or making frequent deposits.

Withdrawals work the same way. If you withdraw $5,000 on the 15th of the month, you lose interest on that $5,000 for the remaining 15 days. If you need the money, withdraw it—the interest loss is usually small. But if you are moving money around for other reasons, timing it to the end of the month means you lose less interest.

Frequently Asked Questions

Is the interest I earn on a savings account taxed?

Yes. Interest earned on a savings account is taxable income. The 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 as ordinary income. The tax rate depends on your overall income and tax bracket, but it could be 22% to 37% of the interest you earned.

Can I earn more interest by moving my money to a different bank?

Yes, if you move to a bank with a higher APY. If your current bank pays 0.05% APY and you move $50,000 to a bank paying 4.5% APY, you earn an extra $2,200 per year. The move itself is free—most banks do not charge to close an account or transfer money out. The only cost is the time it takes to set up the new account and move the funds, which usually takes three to five business days.

What if I make multiple deposits throughout the month?

The bank calculates interest on your average daily balance, so each deposit starts earning interest the day it arrives. If you deposit $1,000 on the 1st and $1,000 on the 15th, the first $1,000 earns interest for the full month and the second earns interest for half the month. The bank does this math automatically—you just see the total interest posted at the end of the month.

Do I lose interest if I withdraw money before the end of the month?

No penalty, but you do lose the interest that money would have earned for the remaining days. If you withdraw $5,000 on the 20th of a 30-day month, you lose interest on that $5,000 for 10 days. The loss is usually a few dollars, not significant unless the amount is very large.

Why do some banks offer much higher APY than others?

Online banks have lower costs because they do not operate physical branches, so they can offer higher rates and still be profitable. Traditional banks with many branches have higher overhead and pass less of their earnings to depositors. Banks also compete for deposits—if one bank raises its rate, others often follow to keep customers from leaving.