Compound Interest Calculator
Estimate future balance, total contributions, and interest growth from principal, monthly deposits, rate, and time.
Calculate your result
Change any value and the estimates update immediately. Nothing entered here is sent to our server.
What this calculator estimates
Compound interest shows how an initial balance, recurring deposits, rate of return, and time can work together. The calculator separates contributions from estimated growth so you can see how much comes from saving versus compounding.
How to use the result
Try different monthly contributions, rates, and time horizons. A longer timeline can matter more than a small rate change, but the estimate should not be treated as a guaranteed return.
Important limitations
Real investments can go down, rates change, inflation reduces purchasing power, and taxes or fees can reduce the ending balance. Use this as a planning tool, not financial advice.
Practical planning tip
Compare a conservative rate with an optimistic rate. If a plan only works with a very high return, it may be too fragile for real-world budgeting.
How to use it
- Enter the starting amount, monthly contribution, annual rate, and number of years.
- Review future value, contributions, and estimated interest.
- Run at least two scenarios before using the estimate in a savings plan.
How the calculation works
The balance compounds monthly using the annual rate divided by 12, with each contribution added at the end of the month. The calculation assumes a constant return and does not subtract inflation, taxes, account fees, or investment losses.
Worked example
A $5,000 starting balance plus $250 per month for 10 years at an assumed 6% return illustrates how contributions and estimated growth combine. Run a lower-rate scenario as a conservative comparison.
Frequently asked questions
Does this predict returns?
No. Market returns are variable and can be negative; the rate is only an assumption.
When are deposits added?
This calculator adds each monthly contribution after that month's growth calculation.
Calculation method and page content last reviewed: July 20, 2026.
Related financial tools
Browse the complete free tools directory for calculators, PDF tools, writing utilities, and business helpers.