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Investment Calculator
Project your investment growth with compound interest, monthly contributions, and inflation adjustment.
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Future Value
Total Contributions
Investment Gain
Inflation-Adjusted Value
Calculated in your browser. We never see your numbers.
Year-by-Year Projection
| Year | Balance | Gain |
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How to Use This Calculator
Enter your initial investment amount — the lump sum you're starting with today. Then set your expected annual return rate; a common benchmark is 7–10% for a diversified stock portfolio over the long term. Choose your investment horizon in years. Optionally, add a monthly contribution to simulate regular investing (dollar-cost averaging). If you want to see the real purchasing power of your future balance, enter an expected inflation rate. Results update instantly as you type, showing future value, total contributions, investment gain, and inflation-adjusted value.
Investment Growth Formula
This calculator uses monthly compounding with optional monthly contributions. The monthly rate is r = annualReturn / 100 / 12 and the number of periods is n = years × 12. The future value is calculated as: FV = initial × (1 + r)^n + monthlyContrib × ((1 + r)^n − 1) / r. For a 0% return, FV = initial + monthlyContrib × n (no compounding). The inflation-adjusted real value is: realValue = FV / (1 + inflationRate/100)^years. For example, $10,000 at 8% annual return for 20 years (no contributions) gives approximately $46,610.
Example Calculation
Suppose you invest $10,000 today and contribute $500 per month for 20 years, earning an 8% annual return. Your total contributions would be $10,000 + ($500 × 12 × 20) = $130,000. However, thanks to compound interest, your portfolio would grow to over $320,000 — meaning you'd gain roughly $190,000 from investment growth alone. If inflation averages 2.5% over that period, the inflation-adjusted real value would be approximately $196,000 in today's dollars. Starting early and contributing consistently makes an enormous difference over time.
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Frequently Asked Questions
What is a realistic stock market return rate?
Historically, the U.S. stock market (S&P 500) has returned an average of about 10% per year before inflation, or roughly 7% after inflation. However, past performance doesn't guarantee future results. Individual years can vary dramatically — from -40% to +50%. For long-term planning, many financial advisors suggest using 6–8% as a conservative estimate for a diversified portfolio.
How does inflation affect my investment returns?
Inflation erodes the purchasing power of your money over time. If your investments return 8% annually but inflation is 3%, your real return is only about 5%. This calculator shows both the nominal future value and the inflation-adjusted real value so you can see what your money will actually be worth in today's dollars. Over 20–30 years, inflation has a substantial impact.
What is dollar-cost averaging?
Dollar-cost averaging (DCA) is the practice of investing a fixed amount of money at regular intervals — such as $500 every month — regardless of market conditions. When prices are low, you buy more shares; when prices are high, you buy fewer. Over time, this strategy lowers your average cost per share and reduces the risk of investing a large amount at a market peak. The monthly contribution field in this calculator simulates DCA.
Should I invest a lump sum or monthly?
Research shows that lump-sum investing outperforms dollar-cost averaging about two-thirds of the time because markets tend to rise over time — so getting money invested sooner generally pays off. However, if you don't have a lump sum available, consistent monthly contributions are the next best approach. Many investors combine both: invest what they have now and continue adding monthly contributions from income.
What is an index fund?
An index fund is a type of mutual fund or ETF that tracks a market index, such as the S&P 500. Instead of trying to beat the market through active management, index funds simply replicate the index's holdings. They typically have very low fees (expense ratios under 0.1%) and have historically outperformed the majority of actively managed funds over the long term. Index funds are widely recommended for long-term investors.
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