The daily balance method is how most banks calculate your interest
Banks calculate interest on high yield savings accounts by taking your account balance at the end of each day, adding up all those daily balances for the month, dividing by the number of days in the month, and then multiplying by the annual percentage yield (APY) divided by 365. This is called the daily balance method, and it is the standard across nearly all online banks and many traditional banks.
The practical effect: if you have $10,000 in the account for the entire month, you earn interest on $10,000. If you deposit $5,000 on the 15th, you earn interest on the original $10,000 for 14 days, then on $15,000 for the remaining days. The bank does not round up or down—it tracks the exact balance each day.
Some banks use a slightly different method called the average daily balance method, which works the same way but is less common in savings accounts. A few older institutions use the minimum balance method, where only your lowest balance during the period earns interest, but this is rare in high yield accounts.
Key Takeaways
- Most banks use the daily balance method, which means interest accrues on your exact balance each day of the month, not just your opening or closing balance.
- Interest is calculated by multiplying your average daily balance by the APY divided by 365, then dividing by the number of days in the month.
- Deposits made mid-month earn interest only from the day they are credited, not retroactively from the start of the month.
- Interest is usually credited to your account monthly, though some banks credit it daily or quarterly depending on their terms.
- The APY you see advertised already accounts for compounding, so you do not need to calculate compound interest separately.
How the calculation actually works: a concrete example
Say you have a high yield savings account with an APY of 4.50%. Your balance on each day of March is:
| Date Range | Daily Balance | Number of Days |
|---|---|---|
| March 1–10 | $20,000 | 10 days |
| March 11–20 | $25,000 | 10 days |
| March 21–31 | $22,000 | 11 days |
The bank adds these up: ($20,000 × 10) + ($25,000 × 10) + ($22,000 × 11) = $200,000 + $250,000 + $242,000 = $692,000. Then it divides by the number of days in March (31): $692,000 ÷ 31 = $22,322.58 average daily balance.
Now multiply by the daily rate. The APY is 4.50%, so the daily rate is 4.50% ÷ 365 = 0.01233%. The interest earned is $22,322.58 × 0.01233% = $2.75. That $2.75 posts to your account, usually on the last day of the month or the first day of the next month, depending on the bank's schedule.
Why the APY already includes compounding
The APY (annual percentage yield) you see advertised is not the same as the interest rate. The APY includes the effect of compounding—the way interest earns interest. If a bank advertises 4.50% APY, that means if you left money untouched for a full year, you would earn 4.50% total, accounting for how often the bank credits interest.
Most high yield savings accounts compound interest daily or monthly. If a bank compounds daily, it calculates interest each day and adds it to your balance, so the next day's interest is calculated on a slightly larger balance. By the end of the year, this compounding effect adds up. The APY already reflects this—you do not need to do any extra math.
If you see an interest rate listed separately from the APY, the rate is the raw percentage before compounding is factored in. Always use the APY when comparing accounts, because it shows the true return you will receive.
When interest posts and how often it compounds
Interest is credited to your account on a schedule set by the bank. Most online banks credit interest monthly, on the last business day of the month or the first day of the next month. Some credit it daily, meaning the interest calculated each day is added to your balance when ready. A few credit it quarterly.
The frequency of crediting affects how much you earn, because credited interest becomes part of your balance and earns interest itself. If a bank credits interest daily, you earn interest on your interest starting the next day. If it credits monthly, you wait until the end of the month to earn interest on that interest. Over a year, daily crediting produces slightly more total interest than monthly crediting, all else equal.
Your bank's account agreement or disclosure statement will specify the crediting schedule. You can usually find this in the fine print on the bank's website or in the document they send when you open the account.
How deposits and withdrawals affect the calculation
A deposit made on the 15th of the month starts earning interest on the 15th. It does not earn interest retroactively from the 1st. The bank counts it in the daily balance only from the day it is credited to your account, which is usually the same day for transfers from another account at the same bank, but can be one to three business days for transfers from outside banks.
Withdrawals work the same way in reverse. If you withdraw $5,000 on the 20th, that $5,000 stops earning interest on the 20th. The interest calculation uses your actual balance on each day, so the withdrawal when ready reduces the balance used to calculate interest for the remaining days of the month.
This is why the timing of large deposits and withdrawals matters. Depositing $10,000 on the 1st versus the 30th can mean a difference of nearly a month's worth of interest on that $10,000.
The difference between stated rate and APY
Banks are required to disclose both the interest rate and the APY. The interest rate is the percentage the bank pays on your balance before accounting for compounding. The APY is the rate after compounding is factored in.
For example, a bank might advertise a 4.40% interest rate with 4.50% APY. The difference exists because the bank compounds interest daily. If you earn interest every day and that interest when ready starts earning interest, you end up with slightly more than 4.40% by the end of the year—you end up with 4.50%.
When you are comparing high yield savings accounts, always compare the APY, not the stated rate. The APY is the true number that tells you how much money you will actually have at the end of a year.
What happens if the APY changes
High yield savings account rates change frequently. Banks raise and lower their APY based on what the Federal Reserve does with its benchmark interest rate. When the Fed raises rates, banks typically raise their APY within days or weeks. When the Fed cuts rates, banks usually cut their APY as well, though sometimes more slowly.
Your bank must notify you before lowering your APY, usually by email or a notice in your account. The new rate takes effect on a date the bank specifies, often 30 days after the notice. Interest earned before that date is calculated at the old rate; interest earned after uses the new rate.
If you lock in a rate, you are not actually locking anything—high yield savings accounts do not offer fixed rates. The rate can change at any time. If you want a may provide rate, you would need a certificate of deposit (CD), which is a different product with a fixed term and fixed rate.
Frequently Asked Questions
Do I earn interest on interest in a high yield savings account?
Yes, if the bank credits interest to your account. Once interest is credited, it becomes part of your balance and earns interest itself. This is compounding. Most banks credit interest monthly or daily, so you start earning interest on your interest when ready or within a month.
Why do I earn less interest than the APY suggests?
The APY assumes you leave money in the account for a full year without deposits or withdrawals. If you deposit money mid-year, withdraw money, or only keep money in the account for part of the year, you earn less than the full APY. The interest you earn is proportional to how long the money sits in the account.
Does the bank round interest up or down?
Banks calculate interest to the cent and credit the exact amount. They do not round up. If your interest is $2.754, you receive $2.75. If it is $2.755, you receive $2.76. The rounding rule is standard: round to the nearest cent, with amounts ending in .5 rounding up.
What if I close my account mid-month?
You receive interest only through the day you close the account. The bank calculates your average daily balance using only the days the account was open, then credits the proportional interest. If you close on the 15th, you earn interest for 15 days, not the full month.
Can I predict exactly how much interest I will earn?
You can estimate it using the daily balance method, but the exact amount depends on the exact balance each day, which only you know. Use your bank's interest calculator if it provides one, or multiply your average expected balance by the APY and divide by 12 for a rough monthly estimate.