Compound Interest Calculator
Estimate how a starting balance and steady monthly contributions may grow over time.
Result
Read the estimate carefully
Monthly compounding
This calculator models a steady annual rate compounded monthly.
Contributions
Monthly contributions are modeled at the end of each month.
Real returns vary
Actual savings or investment returns can change over time and may include taxes, fees, or losses.
Educational planning estimate only; not investment, tax, or financial advice and not a prediction of future returns.
How it works
Compound interest means you earn interest on your interest. Each month, the interest you earned is added to your balance, and next month's interest is figured on that bigger balance. Over many years, this snowball effect can grow your money much faster than simple interest.
This calculator adds interest every month and adds your monthly contribution at the end of each month.
Worked example
Example: You start with $5,000, add $200 every month, and earn 5 percent a year for 10 years.
Money you put in: $5,000 plus $200 times 120 months, which is $29,000.
Estimated balance after 10 years: about $39,291.50.
Growth from interest: about $10,291.50. That is money you did not have to deposit yourself.
Common questions
What is the difference between simple and compound interest?
Simple interest is only figured on the money you put in. Compound interest is also figured on the interest you have already earned, so it grows faster over time.
How often is interest compounded here?
Monthly. The yearly rate is divided by 12 and applied each month.
Is the result guaranteed?
No. Real savings and investment returns change over time. Use this as a planning estimate, not a promise.