Build Your Own Portfolio Simulator
Define your own assets. Give each one an expected return, a volatility, and a weight, set how correlated they are, and this runs 2,000 market paths to show the range of outcomes. For when the presets don't match what you actually hold. Everything runs in your browser.
Your plan
Your assets 100%
| Asset | Return % | Volatility % | Weight % | |
|---|---|---|---|---|
Correlation sets how much your assets move together. It changes the width of the outcome range (your risk), not the median: 0 = they move independently (more diversification, a narrower range), 1 = they move in lockstep (no diversification benefit, a wider range). Weights must total 100% before you run.
Saved only in this browser (no account, nothing uploaded). Load one to restore your assets and plan.
Saved plans
10th – 90th percentile
the range 8 in 10 simulations landed in
Median: half did better, half worse
High: top 10% · Low: bottom 10%
How this works
- Each simulated month your portfolio earns a random return drawn from a lognormal calibrated to your blended expected return and volatility.
- Blend:
μₚ = Σ wᵢ·μᵢ,σₚ = √(ΣΣ wᵢwⱼσᵢσⱼρ), where ρ is your average-correlation input for every pair of different assets (1 for an asset with itself). - Annual → monthly, then 2,000 paths; report the 10th / 50th / 90th percentiles. "Today's dollars" divides by (1.025)^years.
- You supply the return and volatility for each asset, so the output is only as good as those assumptions. They are yours to choose, not forecasts.
How to pick return, volatility, and correlation
- Expected return: the long-run average annual return you expect from the asset. Use its history as a guide: broad stocks roughly 7–10%, bonds 2–4%, gold ~4%, cash ~2%. For a specific ETF, look up its long-term annualized return on its fact sheet or a site like lazyportfolioetf.com. When unsure, use the lower end.
- Volatility: how much the return swings year to year (its standard deviation). Rough guides: broad stocks 15–20%, a single country or sector 18–25%, bonds 4–6%, gold ~15%, cash ~1%. The same fact sheets list it as “standard deviation” or “volatility.”
- Correlation: how much your assets move together (one average value here). Use ~0.6–0.8 if you hold mostly stocks (they move together), ~0.3–0.5 for a stocks-and-bonds mix, and ~0.1–0.3 if you hold genuinely different things (stocks + bonds + gold). Lower correlation is what makes diversification work. It widens or narrows the range of outcomes; it does not change the median.
Illustrative, not financial advice. See the disclaimer.