See how savings grow with compound interest and regular monthly deposits. Starting with $10,000 and adding $500 a month at a 4.00% annual yield (APY), you would have about $88,150 after 10 years: $70,000 of your own money and $18,150 of interest.
Compound Interest Calculator
Savings growth with monthly deposits
- Total deposits
- –
- Interest earned
- –
- Years to double (Rule of 72)
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Year-by-year growth
| Year | Deposits | Interest | Balance |
|---|
Assumes the yield stays the same and deposits are made at the end of each month. Interest is taxable income in most accounts.
How compound interest works
Interest is added to your balance, and the next period’s interest is earned on that larger balance. The calculator converts the APY to a monthly rate, i = (1 + APY)1/12 − 1, adds interest each month and then your deposit.
- Future value of the starting balance = P × (1 + APY)years
- Future value of monthly deposits = deposit × [(1 + i)n − 1] ÷ i, where n is the number of months
Growth over time
| Years | Total deposits | Interest earned | Balance |
|---|---|---|---|
| 5 | $40,000 | $5,256 | $45,256 |
| 10 | $70,000 | $18,150 | $88,150 |
| 20 | $130,000 | $73,832 | $203,832 |
| 30 | $190,000 | $185,069 | $375,069 |
After 30 years, interest makes up almost half of the balance. Time matters more than the rate: the same deposits over 20 years earn $73,832 of interest, but over 30 years they earn $185,069.
The Rule of 72
Divide 72 by the annual rate to estimate how long money takes to double. At 4%, that is about 18 years; at 6%, about 12.
APY vs. APR
APY (annual percentage yield) already includes compounding, so it is the right number to compare savings accounts and CDs. APR is the simple yearly rate before compounding.
FAQ
Is interest taxable?
Yes. Interest from savings accounts and CDs is ordinary income, and banks report it on Form 1099-INT. Interest earned inside retirement accounts such as IRAs and 401(k)s is taxed differently.
Are high-yield savings accounts safe?
Deposits at FDIC-insured banks are insured up to $250,000 per depositor, per bank, per ownership category. Credit unions have similar coverage through the NCUA.
Related calculators
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- Credit Card Payoff CalculatorPay off high-interest debt first
Sources
Figures current as of October 12, 2026
Each formula is checked against a separate test sheet with at least three worked examples. Results are estimates based on the numbers you enter and the published rules; your actual figures may differ. This is general information, not financial or tax advice.
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