APR on savings accounts is calculated by dividing your annual interest rate by 365 days, then multiplying that daily rate by your account balance each day, and adding those daily amounts together

Most banks use the daily balance method. Here's how it works in practice: if your savings account earns 4.50% APR and you have $10,000 in the account, the bank divides 4.50 by 365 to get a daily rate of about 0.0123%. That daily rate is applied to whatever balance sits in your account that day. If you deposit $5,000 on day 15, the daily calculation changes starting day 15 because your balance is now higher. At the end of the month or quarter, the bank adds up all those daily interest amounts and deposits the total into your account.

The reason banks break it into daily pieces instead of calculating once a year is that your balance changes constantly—deposits come in, withdrawals go out. A daily calculation captures those changes and pays you interest on the actual money you held each day, not an average or a guess.

Key Takeaways

  • Banks divide the annual percentage rate by 365 to find the daily interest rate, then apply that rate to your balance each day of the month or quarter.
  • The daily balance method means you earn interest only on money that actually sits in your account—deposits made mid-month start earning interest the day they arrive.
  • Interest is usually credited to your account monthly or quarterly, not daily, even though the calculation happens every day.
  • A higher APR and a larger balance both increase the amount of interest you earn, but the daily calculation ensures you don't lose interest on money you deposit partway through a period.

Why the daily balance method matters to your earnings

If a bank calculated interest only once per year using your opening balance, you would lose money on deposits made during the year. Imagine opening a savings account on January 1 with $1,000, then depositing $9,000 on December 1. A once-yearly calculation would pay you interest only on the $1,000 for the entire year, ignoring the $9,000 you held for a month. The daily method prevents that loss: your $9,000 earns interest for the 31 days it sits in the account.

Some older or smaller banks use the average daily balance method instead. This approach adds up your balance on each day of the month, divides by the number of days, and applies the daily rate to that average. The result is usually very close to the daily balance method, but it can slightly reduce your interest if you make large deposits late in the month. Most major banks and online banks use the daily balance method, which is more favorable to savers.

How deposits and withdrawals change your daily interest

Every transaction shifts the amount of interest you earn going forward. Suppose you have $5,000 in an account earning 4.50% APR. On day 10 of the month, you deposit $2,000. From day 1 to day 9, the bank calculates interest on $5,000. From day 10 onward, it calculates on $7,000. If you withdraw $1,500 on day 20, the calculation drops to $5,500 for the remaining days. Each segment gets its own daily interest amount, and they all add up at the end of the period.

This is why the timing of deposits matters more than people realize. A $5,000 deposit made on day 1 of a 30-day month earns interest for all 30 days. The same $5,000 deposited on day 15 earns interest for only 16 days. Over a year, that difference compounds—early deposits earn noticeably more.

The difference between APR and actual interest paid

The APR is an annual rate, but you don't receive a full year's worth of interest all at once. If your account earns 4.50% APR and you hold $10,000 for one month, you earn roughly one-twelfth of the annual interest, or about $37.50 (before any fees). The bank calculates this by applying the daily rate to your daily balance throughout the month, then deposits the total.

Interest is typically credited monthly or quarterly, depending on the bank's terms. Some banks credit it daily, which means you start earning interest on your interest immediately—a small advantage called compounding. Most online savings accounts credit monthly. The APR is always stated as an annual figure so you can compare accounts fairly, but the actual dollars you receive depend on how long you hold the money and how often interest is compounded.

What happens when APR changes mid-month

Banks can change the APR on savings accounts at any time, and they often do when the Federal Reserve changes interest rates. If your bank lowers the rate from 4.50% to 4.25% on day 15 of a 30-day month, the interest calculation splits: days 1–14 use the 4.50% rate, and days 15–30 use the 4.25% rate. You receive interest on both segments when the month closes.

This means you're never locked into a rate for a full month or quarter. If rates drop, your earnings drop immediately. If rates rise, your earnings rise immediately. Banks are required to notify you of rate changes, usually by email or through your online account, but the change takes effect right away—you don't have to do anything.

How to estimate your monthly interest earnings

To get a rough monthly figure, divide the APR by 12. A 4.50% APR divided by 12 is 0.375% per month. Multiply that by your average balance. If you hold $10,000 for the full month, you earn about $37.50 before the bank credits it. This is an approximation because the daily method is more precise, but it's close enough for planning.

For a more exact number, use your bank's interest calculator if it offers one, or ask customer service to estimate based on your typical balance. Some banks show you the interest earned so far in the current period through your online account, which removes the guesswork entirely.

Frequently Asked Questions

Do I earn interest on interest in a savings account?

Yes, if your bank credits interest daily or monthly. When interest is deposited into your account, that interest amount becomes part of your balance and earns interest itself in the next period. This is called compounding. The more often interest is credited, the more you earn from compounding, though the difference is usually small in savings accounts.

Why do some banks show a different APR than the interest rate?

APR and APY are not the same. APR is the annual percentage rate without compounding. APY (annual percentage yield) includes the effect of compounding. If interest is credited monthly, the APY will be slightly higher than the APR. Banks must disclose both, and APY is the more accurate number for comparing accounts.

Can I lose money if the APR drops?

No. A lower APR means you earn less interest going forward, but you don't lose what you've already earned. Interest already credited to your account stays there. Only future interest earnings are affected by the rate change.

What if I withdraw money mid-month—do I lose interest?

No. You earn interest on the balance you actually held each day. If you withdraw $2,000 on day 20, you've already earned interest on that $2,000 for days 1–19. You simply don't earn interest on it for days 20 onward. Interest already earned is yours to keep.

How often should I check my APR to make sure it's competitive?

Rates change frequently, especially when the Federal Reserve adjusts its rates. Check your current rate every few months and compare it to other banks' offerings. If your rate has dropped significantly below what competitors offer, moving your money to a higher-paying account may be worth the effort.