ATLASPortfolio simulator: put in your stocks and see what could happen
A portfolio simulator shows the range of values your holdings could reach, not a single forecast. In ATLAS you enter any stocks and quantities and simulate horizons from one day to 20 years.
What it does
You build the portfolio yourself: which companies, how many shares of each. ATLAS values it at current prices and shows the range of outcomes, the chance of ending below where you started, and which holding contributes most of the risk.
The horizon is yours to change. A one-month view tells you how rough the next few weeks could be; a ten-year view shows how time narrows the odds of loss while widening the dollar spread. Looking at both is the habit that stops short-term noise from driving long-term decisions.
Worked example with live data
Real ATLAS numbers, prices as of Oct 26, 2026.
Example: $10,000 split equally between AAPL, MSFT and JNJ with a 50% correlation assumption has an estimated yearly volatility of 19%. Across 4,000 simulated years, 1 in 20 ends below $7,622, the middle case is $10,517, 1 in 20 ends above $14,537, and 40% finish below the starting amount.
| Stock | Weight | Yearly volatility | Chance higher in 21 sessions |
|---|---|---|---|
| AAPL | 33% | 18% | 53% |
| MSFT | 33% | 24% | 52% |
| JNJ | 33% | 29% | 52% |
| Portfolio | 100% | 19% | – |
| Measure | Value |
|---|---|
| Bad case | $7,622 |
| Middle outcome after 1 year | $10,517 |
| Good case | $14,537 |
| Chance of ending below the start | 40% |
How ATLAS calculates it
Each stock gets a volatility from its recent daily moves blended with its long-run level (75% recent, 25% long-run). These are combined using the correlations between your holdings, so two similar stocks add more risk together than two unrelated ones. Every stock is given the same long-run return assumption of about 7% a year, because short-term return signals did not beat it in ATLAS testing.
The shape of the distribution comes from a Student-t curve with fat tails, calibrated on about 148,000 past predictions across US and world stocks, so extreme months are not treated as impossible.
Limits you should know
Correlations are estimated from history and rise in a crash, exactly when diversification matters most. The simulation does not know about taxes, rebalancing, fees or what you will do when prices fall.
Where it sits in the plans
The portfolio simulator is available on every plan. Simulations that call paid data providers use a credit allowance that grows with the plan.
Run it on your own numbers
Create an account to use this tool with your stocks, your amounts and your horizon.
Get started →Plans from €3.99 a month.
Frequently asked questions
What is a portfolio simulator?
A portfolio simulator estimates how a set of investments could perform over a chosen period by running many possible scenarios, so you see a range of outcomes instead of one number.
Can I simulate my own portfolio with any stocks and quantities?
Yes. In ATLAS you enter the companies and the number of shares and choose a horizon from one day to 20 years.
Does a portfolio simulator predict returns?
No. It shows how wide the plausible range is and how likely a loss is under stated assumptions. Treat it as a stress gauge, not a forecast.
Why does the simulated range get wider over time?
Uncertainty compounds. Over longer horizons the dollar range widens even though the chance of ending below the start usually falls.
Related tools
- Monte Carlo simulationA Monte Carlo simulation runs thousands of random but realistic price paths and reads the outcomes as a distribution, so you see how wide the possibilities are instead of one guess.
- Crisis simulatorThe crisis simulator replays famous market falls on the portfolio you hold today and tells you, in dollars, how far it could fall and how long it might take to come back.
- Portfolio builderThe ATLAS portfolio builder turns your rules (how long, how much risk, which markets) into three concrete portfolios you can compare side by side.
Stocks used in this example
Open any of them to see the full public page, with fair value, odds and a one-year chart:
Not investment advice. ATLAS estimates come from statistical models and public data; they can be wrong and past results do not predict future ones. Disclaimer