How savings account interest is calculated

Your bank calculates interest by multiplying your account balance by the annual percentage rate (APR), then dividing by the number of days in a year. Most banks use daily compounding, which means they calculate interest on your balance each day, add it to your account, and then calculate the next day's interest on that larger amount. This compounds — your interest earns interest.

The formula banks use is: Daily Interest = (Account Balance × APR) ÷ 365. If your account holds $10,000 and the APR is 4.5%, your daily interest is ($10,000 × 0.045) ÷ 365 = $1.23 per day. That $1.23 gets added to your balance, so the next day's calculation includes it.

The timing matters. Interest accrues (builds up) daily but posts (actually appears in your account) on a schedule your bank sets — usually monthly or quarterly. You do not see the money until it posts, but the accrual starts immediately when you deposit funds.

Key Takeaways

  • Daily compounding means your interest earns interest, so the amount you receive grows faster than simple multiplication of balance times rate.
  • Banks calculate daily interest by dividing your APR by 365, multiplying by your balance, and adding the result to your account each day.
  • Interest accrues daily but typically posts monthly or quarterly, so you will not see the money in your account until the posting date.
  • The APR your bank advertises is the annual rate; the actual monthly deposit is one-twelfth of that, minus any fees your account charges.
  • Moving money in or out changes your balance mid-month, so your interest for that month reflects only the days the money was actually in the account.

The difference between APR and actual monthly interest

The APR (annual percentage rate) is what the bank advertises, but it is not what you earn each month. To find your actual monthly interest, divide the APR by 12. A 4.5% APR account earns roughly 0.375% per month — but that is before compounding and before any fees.

Compounding makes the real number higher. With daily compounding, you earn slightly more than one-twelfth of the annual rate because each day's interest gets added to your balance and earns interest itself. Over a full year, this difference adds up, which is why banks emphasize "daily compounding" in their marketing.

Fees reduce what you actually keep. Some savings accounts charge monthly maintenance fees, inactivity fees, or fees for falling below a minimum balance. These come out of your interest earnings first. A $10,000 account earning $37.50 per month in interest but charged a $5 monthly fee nets you $32.50.

How deposits and withdrawals affect your interest

Your interest is calculated on your actual balance each day. If you deposit $5,000 on the 15th of the month, interest accrues on that $5,000 starting the 15th — not retroactively for the whole month. If you withdraw $3,000 on the 25th, your balance drops and interest for the 25th onward is calculated on the lower amount.

Banks use the average daily balance method or the daily balance method. With daily balance, each day's interest is based on that exact day's balance. With average daily balance, the bank adds up your balance for each day of the month and divides by the number of days — this smooths out the effect of deposits and withdrawals. Most savings accounts use daily balance, which is more favorable to you when you deposit money early in the month.

Timing your deposits matters slightly. Depositing on the 1st instead of the 30th means your money earns interest for 29 more days that month. Over a year, that difference is real but small — roughly one month's worth of interest on that deposit.

How to calculate your expected annual interest

To estimate what you will earn in a year, use this formula: Annual Interest = Account Balance × APR. A $25,000 balance at 4.5% APR earns roughly $1,125 per year before compounding adjusts it slightly upward.

Compounding adds a small bonus. With daily compounding, your actual earnings are slightly higher than the simple calculation because interest compounds. The difference is small on savings accounts — usually less than 0.1% extra — but it grows with larger balances and higher rates. A financial calculator that factors in daily compounding will give you the exact figure, but the simple multiplication gets you within a few dollars.

Your actual earnings will be lower if your balance changes during the year or if your bank charges fees. If you start with $25,000 but withdraw $5,000 in June, your interest for the year is calculated on the lower balance for the second half. If your account charges a $5 monthly fee, subtract $60 from your annual interest estimate.

Why APR varies between banks

Banks set their own APR based on what the Federal Reserve charges them to borrow money, competition in your area, and the type of account. High-yield savings accounts typically offer 4% to 5.5% APR, while traditional savings accounts at large banks often offer 0.01% to 0.5%. The difference is substantial — a $10,000 balance earns $50 per year at 0.5% but $450 per year at 4.5%.

Online banks usually offer higher rates than brick-and-mortar banks because they have lower overhead costs. Credit unions sometimes offer competitive rates to members. The APR also changes over time — when the Federal Reserve raises or lowers its rates, banks adjust their savings rates within weeks or months.

Your account type matters too. Money market accounts sometimes pay higher rates than savings accounts. Certificates of deposit (CDs) lock your money away for a set term but pay more interest. Regular savings accounts are the most flexible but typically pay the least.

Tracking your interest earnings

Your bank statement shows interest posted each month or quarter. Look for a line item labeled "Interest Paid" or "Interest Credited." This is the actual amount that hit your account that period. Add up these deposits across the year to see your total interest earned.

Your bank also sends a 1099-INT form at tax time if you earned $10 or more in interest during the year. This reports your interest income to the IRS. You must report this on your tax return as income, even though it is a small amount.

Many banks let you see your interest calculation in the account details section online. Some show a running total of interest earned year-to-date. If your bank does not display this, you can calculate it yourself by multiplying your average balance by the APR and dividing by 12 for each month.

What happens if your bank changes the APR

Banks can change the APR on savings accounts at any time without notice, though most give you a few days' warning. When the Federal Reserve raises rates, banks usually raise savings rates within a week or two. When the Fed cuts rates, banks often cut savings rates faster.

You do not have to accept a rate cut. If your bank lowers the APR and you find a better rate elsewhere, you can move your money to a different bank. There is no penalty for closing a savings account and transferring your balance. Some people move their savings every few months to chase the highest available rate.

Rate changes do not affect interest you have already earned. If you earned $50 in interest at 4.5% APR and your bank then drops the rate to 3%, that $50 stays in your account. Only future interest is calculated at the new rate.

Frequently Asked Questions

Do I earn interest on interest?

Yes, with daily compounding. Each day's interest gets added to your balance, and the next day's interest is calculated on that larger amount. This is called compound interest. Over a year, this adds a small percentage to your earnings — usually less than 0.1% extra, but it grows with larger balances and longer time periods.

When does interest actually appear in my account?

Interest accrues (builds up) daily but posts (shows up in your account) on a schedule set by your bank — usually monthly or quarterly. You cannot withdraw it until it posts, but it starts earning from the day you deposit your money. Check your account details or call your bank to find out your posting schedule.

What if I withdraw money before interest posts?

You lose the interest that accrued on that money. If you withdraw $5,000 on the 28th and interest posts on the 30th, you do not receive interest on that $5,000 for those two days. Interest is calculated only on money that remains in the account through the posting date.

How do I find the best savings rate?

Compare APR across banks using a rate comparison site or by visiting bank websites directly. High-yield savings accounts at online banks typically offer the highest rates. Rates change frequently, so check current rates before moving your money. A difference of 1% or 2% on a large balance adds up to hundreds of dollars per year.

Is the interest I earn taxable?

Yes. Interest income is taxable as ordinary income. If you earn $10 or more in a year, your bank sends you a 1099-INT form, and you report it on your tax return. Even if you earn less than $10, you should still report it. The amount is usually small, but it counts as income.