Investment Growth Calculator

This free investment growth calculator uses Monte Carlo simulation to project — or forecast — what your portfolio could be worth over any time horizon from 1 to 30 years. Unlike simple compound interest calculators that output a single number, it runs 1,000 independent simulations drawn from an asset's real historical return distribution — showing you the pessimistic, median, and optimistic range of outcomes. Choose from Bitcoin, the S&P 500, NVIDIA, gold, and 35+ other assets. Add a monthly contribution to model ongoing investing. The result is a probability fan chart that gives you a realistic investment forecast — a calibrated range of outcomes, not a false single-number certainty.

Frequently Asked Questions

What is a Monte Carlo investment simulation?

A Monte Carlo simulation models investment growth by running hundreds or thousands of randomized scenarios, each based on the asset's real historical return and volatility. Instead of predicting one outcome, it shows a distribution — so you can see the range from a pessimistic result to an optimistic one, along with the median path.

How is this different from a simple compound interest calculator?

A compound interest calculator assumes a fixed annual return and outputs one number. This investment growth calculator runs 1,000 simulations using the asset's real historical volatility, so the result reflects the actual uncertainty of markets — including scenarios where your investment underperforms or loses value.

What do the percentile bands mean on the chart?

The chart shows three bands: the 10th percentile (pessimistic — 90% of simulations ended higher), the 50th percentile (median — the middle outcome), and the 90th percentile (optimistic — only 10% of simulations ended higher). These give you a calibrated sense of the risk/reward range for your investment over time.

What historical data does the simulator use?

The simulator calculates each asset's mean daily return and standard deviation from real historical price data via Yahoo Finance. It then uses these statistics to generate forward paths using geometric Brownian motion — a standard model in quantitative finance. The longer the historical record, the more robust the simulation parameters.

Can I include regular monthly contributions?

Yes. Enter a monthly contribution amount and the simulator adds it to your portfolio each month across all 1,000 simulations. This lets you model the compounding effect of consistent investing — sometimes called dollar-cost averaging — over your chosen time horizon.

Is this a financial prediction or a projection?

It is a projection based on historical patterns, not a prediction of the future. Past volatility does not guarantee future volatility, and real markets are affected by events that have never happened before. Use this tool for educational insight into how different assets behave over time, not as financial advice.

Can I use this to forecast my investment's future value?

Yes. This is a probabilistic investment forecast tool: instead of forecasting a single future value, it runs 1,000 simulations to forecast the full range of what your investment could be worth in 5, 10, 20, or 30 years. You get a pessimistic, median, and optimistic forecast for any asset, based on its real historical return and volatility.

How accurate is an investment forecast like this?

No investment forecast can predict the exact future — markets are driven by events that have never happened before. What a Monte Carlo forecast does well is calibrate uncertainty: it shows how wide the range of plausible outcomes is for a given asset and time horizon, which is far more honest than a single-number projection. Treat it as an educational range, not a guarantee.