Finance calculator
Compound Interest Calculator
Use this compound interest calculator to model how a starting balance, monthly contributions, return assumptions, and time can affect a future balance estimate. The result is useful for comparing scenarios, but it should not be treated as a guaranteed investment outcome because real returns, taxes, fees, inflation, and market volatility can change the result.
How to use this calculator
- Enter the starting amount and any recurring monthly contribution.
- Add an annual return assumption and time period for the estimate.
- Compare final balance with total contributions to see how much of the estimate comes from modeled growth.
Formula
- Monthly rate = annual return rate / 12
- Final balance grows the starting amount and adds each monthly contribution
- Total contributions = initial amount + monthly contribution x months
- Estimated growth = final balance - total contributions
Example calculation
With $5,000 to start, $300 added monthly, a 6% annual return assumption, and 20 years, the estimated final balance is about $155,163. Contributions total $77,000, and estimated growth is about $78,163.
How to interpret the results
- Compare final balance with total contributions to see how much of the estimate comes from money added versus modeled growth.
- The return rate is only an assumption. Test lower return scenarios, shorter time periods, and reduced contributions before relying on one optimistic result.
- The estimate does not include taxes, fees, inflation, or market volatility, so real results can be materially different.
Frequently asked questions
Is the return rate guaranteed?
No. The return rate is only an assumption for planning and scenario modeling. Real investment returns can vary and may be negative.
How often does this compound?
The calculator uses monthly compounding and assumes contributions are added monthly.
Does this include taxes or fees?
No. Taxes, account fees, inflation, and investment costs can materially affect real results.
Planning disclaimer
MoneyHackWise calculators are for general informational and planning purposes only and do not provide financial, investment, tax, legal, accounting, lending, or business advice. Results are estimates based on the inputs and assumptions shown.
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