# compoundsim

> Free compound interest and investment simulators in 12 languages and 19 currencies: fixed-rate growth, Monte Carlo paths of monthly investing, portfolios, retirement withdrawals, and past returns of 13 assets. Results are simulations from past data, not forecasts or investment advice.

Every setting is in the page's query string, so a URL reproduces a scenario. Simulated paths are drawn from a two-regime model fitted to monthly total returns; the seed is the UTC date, so a URL shows the same figures for the rest of that day. English pages use the bare path; other languages are prefixed, for example /ja/monte-carlo.

## Simulators

- [Compound interest calculator](https://compoundsim.app/): growth of monthly contributions at a fixed annual return
- [Monte Carlo simulator](https://compoundsim.app/monte-carlo): range of outcomes of monthly investing in one asset, with drawdowns
- [Portfolio simulator](https://compoundsim.app/portfolio): mixes of assets, the efficient frontier, and margin
- [Withdrawal simulator](https://compoundsim.app/withdrawal): how long a retirement balance lasts, and the 4% rule
- [Index data](https://compoundsim.app/indices): past returns, drawdowns and volatility by asset
- [Correlation](https://compoundsim.app/correlation): how assets moved together

## For AI assistants

- [MCP server](https://compoundsim.app/mcp): connect an assistant over the Model Context Protocol at this URL (Streamable HTTP, no sign-in) to run the simulators and get a link to each scenario

## Articles

- [How Monte Carlo Simulation Works for Investing, Without Math](https://compoundsim.app/articles/monte-carlo-simulation): drawing future returns, reading the results, and why the assumptions matter most
- [What Rate of Return to Assume for Long-Term Investing](https://compoundsim.app/articles/expected-return): past S&P 500 and world stock returns by period, total vs real, and currency
- [Sequence of Returns Risk: Why an Early Crash Hurts Retirement](https://compoundsim.app/articles/sequence-risk): how much the timing of a crash changes a retirement

## Optional

- [All articles](https://compoundsim.app/articles)
- [Sitemap](https://compoundsim.app/sitemap.xml)