Banks multiply your balance by a daily rate, then add that amount to your account each day

Most savings accounts use daily compounding. The bank takes your current balance, multiplies it by a tiny fraction of the annual interest rate (the daily rate), and deposits that amount into your account. Tomorrow, the calculation includes both your original balance and yesterday's interest. This repeats every day, which is why your balance grows faster than simple math would suggest.

The actual formula banks use is: Daily Interest = (Account Balance × Annual Interest Rate) ÷ 365. If you have $10,000 and the rate is 4.5% per year, the daily interest is roughly $1.23. That $1.23 gets added to your account, and the next day's calculation uses $10,001.23 as the starting balance.

Interest posts to your account on different schedules depending on the bank. Some add it daily but show it only monthly. Others calculate daily but post weekly or quarterly. Check your account statement or the bank's disclosure document to see when interest actually appears in your balance.

Key Takeaways

  • Daily compounding means interest is calculated on your balance every single day, including interest you earned yesterday.
  • The daily rate is the annual interest rate divided by 365, multiplied by your current balance.
  • Interest posts to your account on a schedule set by your bank—daily, weekly, or monthly—even though it is calculated daily.
  • A higher Annual Percentage Yield (APY) accounts for compounding and shows you the real return over a year, while the stated rate does not.
  • Your balance on the day interest is calculated matters; deposits made early in the month earn more interest than deposits made late.

The difference between APR and APY

Banks publish two different rates, and they mean different things. The Annual Percentage Rate (APR) is the simple yearly rate before compounding is factored in. The Annual Percentage Yield (APY) is the rate you actually earn after daily compounding happens all year long.

For example, a savings account might advertise 4.5% APR. Because interest compounds daily, the actual APY is slightly higher—often 4.60% or 4.61%. The difference grows larger as rates rise. At 5% APR, the APY might be 5.13%. Banks are required to show you the APY in their disclosure documents and advertisements, because APY is what you actually receive.

When comparing savings accounts, always look at the APY, not the APR. Two banks might advertise the same APR, but one might compound daily and the other monthly, resulting in different APYs. The APY tells you the true picture.

How your balance affects the amount you earn

The larger your balance, the more interest you earn each day. A $50,000 balance at 4.5% APY earns roughly $2,250 per year, while a $5,000 balance earns roughly $225. The interest calculation is straightforward multiplication: higher balance equals higher daily interest.

The timing of deposits and withdrawals also matters. Money deposited on the first of the month earns interest for the entire month. Money deposited on the 28th earns interest for only a few days. Some banks use the "average daily balance" method, which adds up your balance for each day of the month and divides by the number of days. Others use the "ending balance" method, which only counts what you have on the day interest is calculated. Your bank's disclosure document will tell you which method it uses.

Withdrawals reduce your balance immediately, so they lower the amount of interest you earn that day and going forward. If you withdraw $5,000 mid-month, you lose interest on that $5,000 for the rest of the month.

When interest rates change and how it affects your earnings

Savings account rates are not fixed. Banks change them based on what the Federal Reserve does with its benchmark rate. When the Fed raises rates, banks typically raise savings rates within days or weeks. When the Fed cuts rates, banks usually cut savings rates just as quickly, sometimes faster.

Your interest calculation uses whatever rate is in effect on the day the interest is calculated. If your bank raises the rate from 4.0% to 4.5% on the 15th of the month, your interest for the first 14 days is calculated at 4.0%, and your interest for the remaining days is calculated at 4.5%. The change takes effect immediately, not at the start of the next month.

You can see your bank's current rate on its website or in your online banking portal. Most banks show the APY prominently. If you notice your rate has dropped and you are unhappy with it, you can move your money to a different bank offering a higher rate. There is no penalty for moving savings between banks.

Why high-yield savings accounts earn more

High-yield savings accounts use the same daily compounding method as regular savings accounts, but they offer a much higher APY—often 4.0% to 5.3% depending on current market conditions. The calculation works exactly the same way: daily rate times balance, compounded daily. The only difference is the rate itself.

High-yield accounts are usually offered by online banks or credit unions, not traditional brick-and-mortar banks. Online banks have lower overhead costs, so they pass higher rates to customers. Traditional banks often offer 0.01% to 0.5% APY on regular savings accounts, while online banks offer 4.0% or higher on the same type of account.

The trade-off is access. High-yield accounts may have limited branch access or require you to manage your account online. Some have monthly withdrawal limits, though federal rules changed in 2023 and most limits have been removed. Read the account terms before opening one.

How to calculate your expected interest earnings

You can estimate how much interest you will earn using a simple formula: (Balance × APY) ÷ 12 = Monthly Interest. If you have $20,000 at 4.5% APY, you earn roughly $75 per month, or $900 per year.

This is an estimate because your actual balance may change during the month. If you deposit $5,000 mid-month, your interest for that month will be higher than the estimate. If you withdraw money, it will be lower. But the formula gives you a reasonable picture of what to expect.

Many banks and financial websites offer interest calculators. You enter your balance, the APY, and how long you plan to keep the money, and the calculator shows you the projected total. These calculators account for daily compounding and give you a more precise estimate than the simple formula.

What happens to interest if you close your account

Interest accrues up to the day you close the account. If you close on the 20th of the month, you receive interest for the first 20 days. You do not lose the interest you earned, but you do not earn interest for the remaining days of the month.

The bank will send you the final balance—including all accrued interest—by check or electronic transfer, depending on how you close the account. Make sure you know your final balance before you close, so you can confirm the bank sent you everything you are owed.

If you are moving your money to a different bank, consider timing the transfer for early in the month so your new account starts earning interest sooner. The few days of interest you lose by closing mid-month are usually small, but they add up if you move money frequently.

Frequently Asked Questions

Does my bank round down the interest it calculates?

Banks calculate interest to the penny, but some round down when posting to your account. A calculation that results in $1.234 might post as $1.23. The difference is tiny on individual days, but over a year it can add up to a few dollars. Your bank's disclosure document explains its rounding policy.

What if my balance goes negative—do I owe interest?

If your account goes negative (overdraft), you owe overdraft fees, not interest. Overdraft fees are flat charges, usually $25 to $35 per transaction. Interest does not apply to negative balances in savings accounts. However, if you have a line of credit or loan, negative balances do accrue interest.

Can I earn interest on money I just deposited?

Yes. Interest starts accruing the day the deposit clears and posts to your account. If you deposit money on Monday and it clears by Tuesday, you earn interest starting Tuesday. Deposits that take several days to clear (like checks) do not earn interest until the funds are actually in your account.

Why does my bank show different interest amounts each month?

Your balance changes throughout the month as you make deposits and withdrawals, so the daily interest amount changes too. A month with a higher average balance earns more interest than a month with a lower average balance. This is normal and expected.

Is the interest I earn on a savings account taxable?

Yes. Interest earned on savings accounts 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. This is informational only and not tax advice—consult a tax professional about your specific situation.