Interest is calculated on your daily balance and paid out on a schedule set by your bank
Banks calculate savings account interest by taking the balance in your account each day, applying the annual interest rate to that balance, and then dividing by 365 (or 360, depending on the bank's method). The interest earned each day is tiny—usually a fraction of a cent—but those daily amounts add up and are deposited into your account on a schedule: some banks pay monthly, some quarterly, and a few pay daily or weekly. The actual amount you earn depends on three things: how much money sits in the account, what interest rate the bank offers, and how long the money stays there.
The interest rate itself is set by your bank and can change at any time, though banks must notify you before a rate drops. The rate you see advertised (often called the APY, or annual percentage yield) already includes the effect of compounding—meaning interest earned on your interest. If you deposit $1,000 at 4.5% APY and leave it untouched for a year, you will earn roughly $45, but the exact amount depends on how often the bank compounds and pays out the interest.
Key Takeaways
- Banks calculate interest on your daily balance, meaning the amount changes every time you deposit or withdraw money.
- The APY (annual percentage yield) shown by the bank already accounts for compounding, so you do not need to calculate that separately.
- Interest is usually paid monthly or quarterly, not daily, even though it is calculated daily.
- Moving money in or out of the account changes your daily balance and therefore changes how much interest you earn that day.
- The interest rate can change at any time, and banks must notify you before lowering the rate on your account.
How daily balance interest works
Your bank looks at the balance in your account at the end of each day (or sometimes at the beginning of the day—the method varies by bank). It takes that day's balance, multiplies it by the annual interest rate, and divides by 365. That gives you the interest earned for that one day. If you have $5,000 in the account and the rate is 4.5%, the calculation for one day is: ($5,000 × 0.045) ÷ 365 = $0.616 earned that day.
The bank repeats this calculation every single day. On a day when you deposit $2,000, the balance is higher, so the interest earned that day is higher. On a day when you withdraw $1,000, the balance is lower, so the interest earned that day is lower. All those daily interest amounts are added together, and at the end of the month (or quarter, depending on your bank), the total is deposited into your account as a single payment.
This is why the timing of deposits and withdrawals matters. If you deposit a large sum on the first day of the month, that money earns interest for the entire month. If you deposit the same sum on the last day of the month, it only earns interest for one day. Over a year, the difference can be significant.
The difference between APY and interest rate
Banks advertise two numbers: the interest rate (sometimes called the APR for savings accounts) and the APY. The interest rate is the base percentage the bank applies to your balance. The APY is the effective rate you actually earn after accounting for compounding—the fact that interest gets added to your account and then earns interest itself.
For example, a bank might offer a 4.4% interest rate compounded monthly. After one year, the actual return is 4.5% APY because the interest paid each month gets added to your balance and earns interest the following month. The APY is always equal to or higher than the interest rate. When you see an advertised rate for a savings account, it is almost always the APY, which is the number that matters for comparing accounts.
You do not need to calculate APY yourself. The bank does this and shows you the number. What matters is that you compare APY across banks when choosing an account, because a difference of even 0.5% APY can mean hundreds of dollars over several years on a large balance.
When interest is actually deposited into your account
Interest is calculated daily, but it is not deposited daily at most banks. Instead, the bank adds up all the daily interest earned during a period (usually one month or one quarter) and deposits the total as a single payment. Some online banks deposit interest monthly; others quarterly. A few high-yield savings accounts deposit interest daily or weekly, which means you start earning interest on that interest sooner.
The schedule matters because of compounding. If interest is deposited monthly, you earn interest on the new balance starting the next day. If interest is deposited quarterly, you wait three months before that interest starts earning interest itself. Over many years, more frequent deposits mean slightly higher total earnings, but the difference is usually small unless you have a very large balance.
You can find your bank's interest payment schedule in the account disclosures or by calling customer service. The schedule is set by the bank and does not change, though the amount of interest paid each period will vary based on your balance and the current interest rate.
How interest rates change and what that means for you
Banks set their own interest rates and can change them at any time. Rates usually move when the Federal Reserve changes its benchmark rate, but banks do not have to match that change immediately or at all. Some banks raise rates quickly to attract new customers; others lower rates slowly to keep existing customers from leaving.
If your bank lowers the interest rate on your savings account, the bank must notify you in writing before the change takes effect. You have the right to close the account without penalty if you disagree with the new rate. If the bank raises the rate, there is no requirement to notify you first, though most banks do because it is good marketing.
The interest rate on your account is not locked in. Unlike a certificate of deposit (CD), which guarantees a rate for a set period, a savings account rate can change at any time. This is why it makes sense to shop around periodically—if another bank offers a higher rate, you can move your money and start earning more.
How balance changes affect your interest earnings
Every deposit and withdrawal changes your daily balance, which changes how much interest you earn. If you deposit $10,000 on the first of the month and leave it untouched, that full amount earns interest for 30 days. If you deposit $1,000 each day for 30 days, the average daily balance is much lower, so you earn less total interest even though you end up with the same $30,000 at the end of the month.
This is why keeping a steady, high balance in your savings account earns more interest than moving money in and out frequently. Banks use the daily balance method specifically because it rewards customers who maintain larger balances. If you are saving toward a goal and can deposit a lump sum early, you will earn more interest than if you add money gradually.
Some banks offer a different calculation method called the average daily balance, which adds up all your daily balances for the month and divides by the number of days. This method is less common for savings accounts but more common for checking accounts that pay interest. The result is usually very similar to the daily balance method, but it can slightly reduce the impact of a single large withdrawal late in the month.
Interest on money you withdraw before the end of the period
If you deposit money and then withdraw it before the interest payment date, you still earn interest on that money for the days it was in the account. The bank calculates interest based on your daily balance, so the interest is earned day by day. If you deposit $5,000 on the first of the month and withdraw it on the 15th, you earn interest for 15 days, not zero.
This is different from a CD, where withdrawing early before the maturity date usually means losing some or all of the interest. In a regular savings account, there is no penalty for withdrawing money, and you keep all the interest earned up to that point. This is one reason savings accounts are more flexible than CDs—you can access your money without losing earnings.
Frequently Asked Questions
Does interest compound daily or monthly?
Interest is calculated daily, but it is compounded (added to your balance to earn interest itself) on whatever schedule your bank uses to deposit interest—usually monthly or quarterly. The APY already reflects the compounding schedule, so you do not need to calculate it yourself. A higher APY means more frequent compounding or a higher base rate.
If I withdraw money mid-month, do I lose all the interest?
No. You earn interest for each day the money is in the account. If you withdraw on the 15th of the month, you keep the interest earned for those 15 days. Interest is calculated daily, not monthly, so partial-month balances still generate earnings.
Why do different banks offer different interest rates?
Banks set their own rates based on their costs, competition, and business strategy. Online banks often offer higher rates because they have lower overhead than brick-and-mortar branches. Rates also depend on how much money the bank needs to attract and what it can earn by lending that money out.
Can a bank lower my interest rate without warning?
A bank can lower your rate, but it must notify you in writing before the change takes effect. You can close the account without penalty if you do not accept the new rate. Banks do not have to notify you before raising a rate, though most do.
Is the APY may provide for a year?
No. The APY can change at any time on a regular savings account. If you want a may provide rate, you need a certificate of deposit (CD), which locks in a rate for a specific period. Savings accounts are variable-rate products.