Investment Calculator
See how compound interest grows your savings over time with adjustable contributions and inflation.
Investment Breakdown
Growth Timeline
Return Rate Scenarios
Annual Progress
Year-by-Year Details
| Year | Total Invested | Interest Earned | Portfolio Value | Annual Interest | Interest % |
|---|
How It Works
The Investment Calculator models the future value of a portfolio that grows by compound interest while you make recurring contributions. Enter your starting balance, monthly contribution, expected annual return rate, and time horizon, and the tool projects the portfolio month by month, displaying the final balance, total amount contributed, and total interest earned alongside an interactive chart that shows how compounding accelerates growth in the later years. The math uses monthly compounding (the rate is divided by 12 and applied each month) and assumes contributions are made at the start of each month, matching the typical convention used by retirement-account brokers. The tool also accepts an inflation rate so you can compare nominal balances against real (inflation-adjusted) purchasing power — a critical distinction for any horizon longer than five years. Adjust any input and the chart and summary update instantly. Everything runs in your browser, so the numbers you punch in — your savings rate, salary, retirement target — never leave your device.
Worked Example
Start with $10,000, add $200 every month, and assume a 7% annual return compounded monthly for 20 years. The projection reaches about $144,573 — of which only $58,000 is money you contributed; the remaining $86,573 is compound growth, more than half the final value. Enter 2.5% inflation and the calculator also shows the result in today’s purchasing power: about $88,229. The year-by-year chart makes the curve obvious: growth is slow for the first decade, then the interest-on-interest effect visibly takes over.
Use Cases
- Projecting the future value of a retirement account
- Comparing the impact of different contribution amounts
- Understanding how compound interest accelerates growth over time
- Planning how much to invest monthly to reach a financial goal
Frequently Asked Questions
- Is the rate I enter compounded annually or monthly?
- Monthly. The tool divides the annual rate by 12 and compounds each month, which matches how brokerage statements and most retirement calculators report.
- How do I model inflation?
- Enter an inflation rate; the tool shows both the nominal final balance and its purchasing power in today's money. For long horizons, real returns are what matter.
- What return rate should I assume?
- Historically the broad US stock market has returned about 10% nominal / 7% real long-term, but past performance does not guarantee future results. Conservatively model 6–8% nominal for a diversified portfolio.
- Does it account for taxes?
- No. Returns are gross of tax. For tax-advantaged accounts (401k, IRA, ISA), this is a reasonable simplification; for taxable accounts you should reduce the rate by your effective tax drag.
- Are my numbers sent anywhere?
- No. Projections run entirely in your browser.