Monte Carlo Portfolio Simulator

What is Monte Carlo Portfolio Simulator?

The Monte Carlo Portfolio Simulator uses 20 years of real US stock market data (2006-2025) to run 10,000 random portfolio simulations and find your optimal asset allocation. Instead of guessing what percentage to put in NVDA versus SPY versus QQQ, the simulator runs thousands of combinations and identifies the allocation with the best risk-adjusted return — measured by the Sharpe Ratio.

You can choose from 44 assets including major US stocks (NVDA, GOOGL, AAPL, MSFT, TSLA, AMZN) and ETFs (SPY, QQQ, VTI, SCHD, TLT). The simulator calculates three key portfolio types: Maximum Sharpe Ratio (best efficiency), Minimum Volatility (lowest risk), and a Custom allocation you design yourself.

The output is a fan chart showing your portfolio's probability distribution across time — the median path, the optimistic 90th percentile, and the pessimistic 10th percentile — so you understand not just the expected outcome but the full range of realistic possibilities.

Why Use This Tool?

Single-number projections — 'your portfolio will be worth $X in 20 years' — are dangerously misleading. The stock market is not predictable in a straight line: returns are volatile, sequence matters, and the range of outcomes is wide. The Monte Carlo method explicitly models this uncertainty.

By running 10,000 different random-walk scenarios based on actual historical return distributions, the simulator shows you what the realistic best case, worst case, and most likely case look like. This lets you ask better questions: 'Can I afford this allocation if I get the worst 10% outcome?' If yes, you have a robust portfolio. If not, you need to adjust.

How to run a Monte Carlo portfolio simulation

1
Open the Monte Carlo Simulator
Click Open Tool below to access the simulator. It runs entirely in your browser — no download or login needed.
2
Select your assets
Choose from the list of 44 US stocks and ETFs. You can add multiple assets including NVDA, GOOGL, SPY, QQQ, TSLA, AAPL, and more. Start with 3-5 assets for a manageable analysis.
3
Set your allocation (optional)
For the Custom Portfolio option, enter the percentage you want in each asset. Percentages must sum to 100%. For Maximum Sharpe and Minimum Volatility portfolios, the simulator finds the optimal weights automatically.
4
Set your investment amount and period
Enter your initial portfolio value and the investment horizon in years. Typical inputs are $10,000-$100,000 initial value and 10-30 year horizon.
5
Run the simulation
Click Calculate or Run Simulation. The tool runs 10,000 scenarios and displays results in seconds.
6
Read your results
The fan chart shows median, 10th percentile (bad scenario), and 90th percentile (good scenario) paths. The table shows optimal weights for Maximum Sharpe and Minimum Volatility portfolios, plus Sharpe Ratio and annualized return for each.

Frequently Asked Questions

What is a Monte Carlo simulation for investing?

A Monte Carlo simulation runs thousands of random-walk scenarios using historical return distributions to show the full range of possible portfolio outcomes. Instead of one projected number, you get a probability distribution — showing best case, worst case, and everything in between.

How many assets are available in this simulator?

The EZLONG Monte Carlo Portfolio Simulator includes 44 US stocks and ETFs: NVDA, GOOGL, AAPL, MSFT, TSLA, AMZN, SPY, QQQ, VTI, SCHD, TLT, and more. All are based on 20 years of real data (2006-2025).

What is the Sharpe Ratio and why does it matter?

The Sharpe Ratio measures how much return you get per unit of risk (volatility). A higher Sharpe Ratio means better risk-adjusted efficiency. The Maximum Sharpe portfolio gives you the best return-per-risk combination — not necessarily the highest absolute return, but the most efficient use of risk.

What is the Minimum Volatility portfolio?

The Minimum Volatility portfolio is the allocation that achieves the lowest possible portfolio volatility given your chosen assets. It suits risk-averse investors who prioritize capital preservation over maximum growth.

What does the fan chart show?

The fan chart displays three paths over your investment horizon: the 90th percentile (top 10% of simulated outcomes — optimistic case), the 50th percentile (median), and the 10th percentile (bottom 10% — pessimistic case). All three bands are shown simultaneously so you see the full range of realistic outcomes.

How is this different from a simple compound return calculator?

A simple compound calculator assumes constant returns every year (e.g., 10% every year). Monte Carlo simulation uses random returns each year based on historical distributions, capturing the real volatility of markets. This gives a much more realistic picture of long-term investing uncertainty.

What is the efficient frontier?

The efficient frontier is the set of portfolios that offer the highest expected return for a given level of risk. Portfolios on the frontier are efficient — you cannot get more return without taking more risk, and you cannot reduce risk without sacrificing return. The simulator plots your portfolio on this frontier.

Is this Monte Carlo simulator free?

Yes, completely free. No login, no email, no subscription. The simulator runs 10,000 scenarios in your browser using 20 years of real data at no cost.

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