Investment Calculator
A simple compound interest investment calculator. Enter an initial amount, monthly contribution, expected annual return, and time period to see a projected future value.
Use this investment calculator to explore “what if” scenarios: how much a lump sum might grow, how regular monthly contributions change the outcome, and how sensitive long-term results are to your assumed return.
It’s a planning tool, not advice. Markets don’t move in straight lines, and fees and taxes can materially change results.
How to use the investment calculator
Three inputs and you have a projection.
1. Enter amounts
Add your initial investment and a monthly contribution (optional).
2. Set return & years
Use an annual expected return and your investment time horizon.
3. Compare scenarios
Try a conservative return and a higher return to see the range.
Common use cases
Compound interest projection
See how an initial amount could grow over time with a steady expected return.
Monthly contribution planning
Test how different monthly contributions change the end value over years.
Goal targeting
Roughly estimate what it takes to reach a target number by a certain date.
Scenario comparison
Try conservative vs aggressive assumptions to understand the range of outcomes.
Compound interest (high level)
What the projection is doing under the hood.
The projection compounds the initial amount and each periodic contribution over the time horizon using your expected annual return. Returns are applied monthly to match monthly contributions.
If you’re planning for retirement income needs (inflation-adjusted), use the retirement calculator.
Common pitfalls
Confusing return with guaranteed growth
The expected return is an assumption. Real portfolios fluctuate and may underperform for long periods.
Ignoring inflation
A nominal end value may buy less in the future. Use the retirement calculator for inflation-adjusted planning.
Mixing monthly and yearly rates
Enter return as an annual percentage. The calculator handles monthly compounding internally.
Forgetting fees and taxes
Broker fees, fund expense ratios, and taxes can reduce long-term returns and aren’t modeled here.
What this tool supports
| Feature | Supported | Notes |
|---|---|---|
| Initial investment amount | Yes | Start with a lump sum. |
| Monthly contributions | Yes | Model consistent monthly adds. |
| Compound growth | Yes | Uses an annual expected return. |
| Year-by-year view | Yes | Shows a simple progression over time. |
| Signup required | No | No account needed. |
Frequently Asked Questions
User reviews
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Ready to run a scenario?
Enter an amount, pick a return, and see the projection instantly.