Interest adds to your account balance on a schedule set by your bank

Interest is money your bank pays you for keeping money in your account. The bank lends out the money you deposit, earns profit on those loans, and shares a small portion of that profit with you as interest. How much you earn depends on three things: the amount you have saved, the interest rate your bank offers, and how often the bank calculates and adds interest to your account.

Most banks add interest monthly or daily. Some add it quarterly (four times a year). The more often interest is added, the more you earn, because you start earning interest on the interest itself. This is called compounding. A bank that compounds daily will pay you slightly more than one that compounds monthly, even if both offer the same annual rate.

You do not have to do anything to earn interest. Once you open the account and deposit money, the interest accrues automatically. You will see the balance grow each time the bank posts interest, usually on a specific day of the month or at the end of each day.

Key Takeaways

  • Interest is calculated based on your account balance, the annual interest rate, and how often the bank compounds (adds interest to your balance).
  • Compounding means you earn interest on your interest, so accounts that compound daily will grow faster than those that compound monthly at the same rate.
  • The annual percentage yield (APY) shown by your bank already accounts for compounding, so it is the true rate you will earn over one year.
  • Interest rates vary widely between banks and account types, so comparing rates before opening an account can significantly increase what you earn.

How the calculation works: principal, rate, and time

The basic formula is simple: Interest = Principal × Rate × Time. Your principal is the amount you have deposited. The rate is the annual interest rate (usually shown as a percentage). Time is how long the money sits in the account, measured in years or fractions of a year.

If you deposit $1,000 in an account with a 4% annual rate and leave it untouched for one year, you earn $40 in interest ($1,000 × 0.04 × 1). After one year, your balance is $1,040. If you leave that $1,040 in the account for another year at the same rate, you earn $41.60 in interest ($1,040 × 0.04 × 1), because now the interest is calculated on the larger balance. That extra $1.60 is the result of compounding.

Banks do not wait a full year to add interest. They divide the annual rate by the number of times they compound per year. If a bank compounds monthly, it divides the annual rate by 12 and applies that smaller rate to your balance each month. If it compounds daily, it divides by 365. This means you earn a small amount of interest many times throughout the year instead of all at once.

The difference between APR and APY

APR (annual percentage rate) is the simple annual interest rate without compounding factored in. APY (annual percentage yield) is the rate you actually earn when compounding is included. APY is always equal to or higher than APR for savings accounts.

Banks are required to show you the APY, not the APR, when advertising savings accounts. This is the number that matters for your decision. A savings account advertising 4.00% APY will earn you exactly 4% over one year if you do not add or remove money. An account with 3.99% APY compounded daily might actually earn you more than one with 4.00% APY compounded monthly, depending on the exact numbers, so always compare the APY figure.

The difference between APR and APY grows larger the higher the interest rate and the more often interest compounds. At very low rates (under 0.5%), the difference is tiny. At higher rates (4% or above), compounding can add noticeably to your earnings over time.

What happens when you add or withdraw money

Interest is calculated on your balance at the time the bank compounds. If you deposit $500 on the first of the month and the bank compounds on the last day of the month, that $500 earns interest for the full month. If you deposit $500 on the 29th and the bank compounds on the 30th, you earn interest for only one or two 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 daily balance method, which calculates interest on your exact balance each day. A few still use the minimum balance method, which pays interest only on the lowest balance you held during the compounding period. The method your bank uses affects how much you earn, especially if you move money in and out frequently.

Withdrawals work the same way. Money you remove stops earning interest immediately. If you withdraw $200 before the compounding date, that $200 earns no interest for that period. This is why keeping money in the account longer generally results in more interest earned.

How interest rates change and what that means for you

Banks set their own interest rates and change them based on what the Federal Reserve does. When the Fed raises its benchmark rate, banks usually raise savings account rates within days or weeks. When the Fed cuts rates, banks lower savings account rates just as quickly. This means the rate you earn today might be different from the rate you earn three months from now.

Some accounts offer a fixed rate that does not change for a set period (usually three months to one year). Others offer variable rates that can change at any time. High-yield savings accounts typically offer higher rates than traditional savings accounts, but those rates can drop if the Fed cuts rates or if the bank decides to lower them.

You can move your money to a different bank if your current bank's rate falls too far behind what competitors offer. There is no penalty for moving savings account money, though you may want to keep a small amount in your original account if it has other benefits you value.

How to track your interest earnings

Your bank sends you a statement each month (or you can view it online anytime) that shows interest posted to your account. The statement lists the date interest was added and the amount. Over time, you can add up these deposits to see your total earnings. Most online banking platforms also show a running total of interest earned year-to-date.

If you want to estimate future earnings before opening an account, use a savings calculator. You enter your principal, the APY, and how long you plan to keep the money, and the calculator shows you the projected balance and total interest earned. These calculators assume the rate stays the same and you do not add or withdraw money, so actual results will differ if either of those things changes.

At tax time, banks report interest earned to the IRS on a Form 1099-INT if you earned $10 or more in interest during the year. You must report this interest as income on your tax return, even though you did not receive a paycheck. Keep your bank statements or year-end interest summary for your tax records.

Frequently Asked Questions

Does interest compound on money I just deposited?

Yes, but only from the date you deposit it. If you deposit money on the 15th and the bank compounds on the 30th, that money earns interest for 15 days. Money deposited after the compounding date earns interest starting with the next compounding period.

What is the difference between a savings account and a money market account in terms of interest?

Money market accounts typically offer higher interest rates than savings accounts, but they often require a larger minimum balance and limit how many withdrawals you can make per month. Both earn interest the same way—through compounding on your balance. The rate difference depends on the bank and current market conditions.

Can I lose money in a savings account?

No. Your principal is protected by FDIC insurance (up to $250,000 per account). Interest only adds to your balance; it never subtracts. The only way your balance shrinks is if you withdraw money or if fees are charged, though most savings accounts have no monthly fees.

Why do some banks offer much higher interest rates than others?

Online-only banks have lower overhead costs than banks with physical branches, so they can pass higher rates to customers. Credit unions sometimes offer competitive rates to members. Traditional banks with many branches often offer lower rates because they spend more on staff and buildings. Shop around to find the highest rate available.

Does interest stop accruing if I do not log into my account?

No. Interest accrues automatically whether you check your balance or not. You do not need to do anything to earn it. The bank calculates and adds interest on its schedule regardless of your activity.