How savings account interest actually works
Your bank pays you interest on the money you keep in a savings account. The amount you earn depends on three things: how much money sits in the account, what interest rate the bank offers, and how often the bank compounds the interest (adds earned interest back into your balance so you earn interest on that interest too).
Most banks compound interest daily or monthly. This means if you earn $1 in interest one day, the next day you earn interest on that $1 plus your original balance. Over months and years, this compounding adds up. A bank will tell you its interest rate as an Annual Percentage Yield (APY), which already accounts for compounding, so you do not have to do that math yourself.
The formula is straightforward: multiply your account balance by the APY, then divide by 365 (or 12 for monthly compounding). If you have $10,000 in an account with a 4.5% APY, you earn roughly $450 per year, or about $37.50 per month. Banks calculate and deposit this interest automatically.
Key Takeaways
- Interest earned equals your account balance multiplied by the Annual Percentage Yield (APY) divided by the number of days in a year.
- APY already includes the effect of compounding, so you do not need to calculate that separately.
- Your bank statement or online account dashboard shows the exact interest you earned each month.
- Comparing APY rates between banks matters more than the balance itself, because even small differences in rate add up over time.
- Interest rates change, so the amount you earn this month may differ from next month if your bank adjusts its APY.
Where to find your account's APY
Your bank publishes its APY on its website, usually on the savings account product page. Look for a section labeled "Rates" or "APY." The rate shown is the one you earn right now, but banks change rates frequently—sometimes weekly—so the rate you see today may not be the rate next month.
You can also find your APY in your account agreement, which the bank gave you when you opened the account. If you cannot find it, log into your online banking portal and look for account details or disclosures. Most banks also send an updated disclosure by mail or email when they change the rate.
Do not confuse APY with APR (Annual Percentage Rate). APR is used for loans and credit cards; APY is what banks pay you on savings. APY is always the number you need for a savings account.
Doing the math yourself
If you want to calculate interest by hand, use this formula:
Interest earned = (Account balance × APY) ÷ 365
This gives you the interest you earn in one day. Multiply by 30 or 31 to estimate a month, or by 365 to estimate a year. For example, with a $5,000 balance and 4.5% APY: ($5,000 × 0.045) ÷ 365 = $0.62 per day, or about $18.75 per month.
This is an estimate because your balance changes when you deposit or withdraw money, and because banks use different methods to count days. The exact amount your bank calculates may be slightly different. The easiest way to see the real number is to check your monthly statement—your bank has already done the work.
Why your interest changes month to month
Three things cause your interest earnings to fluctuate. First, your balance changes when you deposit or withdraw money. A larger balance earns more interest; a smaller one earns less. Second, the bank's APY changes. If rates rise, you earn more; if rates fall, you earn less. Third, some months have more days than others, which affects daily compounding.
If you deposit $2,000 mid-month, you earn interest only on that $2,000 for the remaining days of the month. If you withdraw $1,000, your balance drops and so does your interest for that month. Banks calculate interest based on the balance on each day of the month, so timing matters.
High-yield savings accounts versus regular savings accounts
A high-yield savings account pays a much higher APY than a regular savings account at the same bank. Regular savings accounts at large banks often pay 0.01% to 0.05% APY. High-yield accounts at online banks or credit unions often pay 4% to 5.35% APY. On a $10,000 balance, that difference means $1 per year versus $400 to $535 per year.
High-yield accounts have the same safety protections as regular savings accounts—your money is insured by the FDIC up to $250,000 per account holder per bank. The trade-off is that high-yield accounts sometimes have higher minimum balances or monthly fees if your balance drops below a threshold. Check the account terms before opening one.
If you are keeping money in a regular savings account at a large bank, you are likely earning very little interest. Moving that money to a high-yield account at an online bank or credit union can double or triple your earnings without any risk to your money.
Using online calculators to estimate earnings
Many banks and financial websites offer free savings calculators. You enter your starting balance, the APY, and how long you plan to keep the money, and the calculator shows you the total interest you will earn. These are useful for comparing accounts or deciding whether to move money to a higher-rate account.
Keep in mind that calculators assume your APY stays the same for the entire period. In reality, rates change. A calculator can show you what you might earn if rates hold steady, but it cannot predict future rate changes. Use it as a rough guide, not a may provide.
Reading your bank statement
Your monthly bank statement lists the interest you earned that month in a line item labeled "Interest Paid" or "Interest Earned." This is the actual amount your bank calculated based on your daily balance and its compounding method. This number is always more accurate than any calculation you do yourself, because the bank knows exactly how it compounds interest and what your balance was each day.
If you notice the interest amount is much lower than you expected, check whether your APY changed during the month or whether your balance was lower than you thought. If the number still seems wrong, contact your bank and ask them to explain how they calculated it. Banks are required to show you the math if you ask.
Frequently Asked Questions
Does interest compound daily or monthly?
It depends on the bank. Most banks compound daily, which means interest is calculated and added to your balance every day. Some compound monthly or quarterly. Daily compounding earns you slightly more money because you earn interest on the interest more often. Your bank statement or account disclosure will tell you the compounding frequency.
If I withdraw money mid-month, do I lose all the interest for that month?
No. Banks calculate interest based on your daily balance, so you earn interest on the money for the days it was in the account. If you withdraw $1,000 on the 15th of a 30-day month, you earn interest on the full balance for 14 days and the reduced balance for 16 days. You do not lose the interest you already earned.
Why is my APY different from the APR I see advertised?
APY and APR are different things. APY (Annual Percentage Yield) is what banks pay you on savings and already includes compounding. APR (Annual Percentage Rate) is what you pay on loans and does not include compounding. For a savings account, always look at the APY, not the APR.
Can I predict exactly how much interest I will earn next year?
No, because interest rates change. You can estimate based on today's APY, but if the bank raises or lowers its rate during the year, your actual earnings will be different. The only way to know for certain is to wait until the year ends and look at your statements.
Is the interest I earn on a savings account taxable?
Yes. Interest earned on a savings account is taxable income. If you earn $10 or more in interest during a calendar year, your bank will send you a 1099-INT form by January 31 of the following year. You report this income on your tax return. This guide covers only how to calculate the interest itself, not tax treatment.