Investment Growth Simulator
See how compound interest grows your money over time. Adjust inputs and plan your financial future.
Parameters
| Year | Deposits | Interest | Balance |
|---|
How to Use This Simulator
Start by entering your initial investment amount, how much you plan to deposit each month, your expected annual return rate, and how many years you plan to invest. The chart and summary update instantly as you adjust any input. Use the sliders for quick exploration or type exact values in the input fields.
Try the preset buttons at the top to load common investment scenarios. Each preset configures realistic parameters based on historical data or common strategies, giving you a useful starting point to explore from.
Understanding Compound Interest
Compound interest is interest earned on both your original investment and on previously earned interest. Over time, this creates exponential growth — your money earns money, and that money earns more money. The longer your investment period and the higher your return rate, the more dramatic this compounding effect becomes.
For example, investing $500 per month at a 7% annual return for 30 years results in $180,000 of deposits — but your total balance would grow to over $566,000. More than two-thirds of your final wealth comes from compound interest, not from the money you put in.
Fees, Taxes, and Inflation
Real-world investing involves costs that reduce your effective returns. The expense ratio represents the annual management fee charged by funds, typically ranging from 0.03% for index funds to over 1% for actively managed funds. Even a small difference in fees compounds significantly over decades.
Capital gains tax is applied to your total interest earned when you withdraw. The inflation adjustment shows your portfolio's value in today's purchasing power, giving you a more realistic picture of future wealth.
What Is the FIRE 4% Rule?
The 4% rule is a widely referenced guideline in the FIRE (Financial Independence, Retire Early) community. It suggests that you can safely withdraw 4% of your investment portfolio annually in retirement without running out of money over a 30-year period. This simulator applies the 4% rule to your projected final balance, showing how much passive income your investments could generate each month, year, and day.
Volatility Range (Monte Carlo Lite)
Real markets don't deliver a consistent return every year. The volatility range feature adds a shaded band to the chart representing optimistic and pessimistic scenarios based on historical standard deviations. This gives you a more realistic picture of possible outcomes rather than a single idealized growth line. The band shows the range between the 10th and 90th percentile of likely outcomes.
Reviewing the volatility range is especially valuable when planning for long time horizons, where the gap between best-case and worst-case outcomes widens significantly. Use it to stress-test your plan and ensure you are comfortable with the downside before committing to an investment strategy.