# cFIREsim

Run a withdrawal plan against every market cycle since 1871 and count how many survived.

*https://stockmarketstack.com/tools/cfiresim · Retirement & FIRE Calculators*

## Facts

### At a glance

| Field | Value |
| --- | --- |
| Vendor | Lauren Boland |
| Category | Retirement & FIRE Calculators |
| Job | retirement |
| Website | https://www.cfiresim.com |
| Pricing model | free |
| Free tier | true |
| Open source | false |
| Licence | none |
| Self-hosted | false |
| Tested hands-on | false |
| Last updated | 2026-09-13 |

### Pricing

| Tier | USD | Period |
| --- | --- | --- |
| Free | 0 USD | month |

### Coverage

| Field | Value |
| --- | --- |
| Asset classes | stocks, bonds, commodities |
| Markets | us |
| Works outside the US | false |
| Data latency | none |
| Platforms | web |
| AI features | none |

### Interfaces

| Field | Value |
| --- | --- |
| API | false |
| Webhooks | false |
| Scripting | none |
| Python | false |
| Spreadsheet add-in | false |
| MCP server | false |
| Export | csv |

### Capabilities

Yes: backtesting

No: charting, screening, scanning, automation, live_trading, paper_trading, portfolio_tracking, broker_import, tax_reporting, alerts, news, options_analysis

*Verified: pricing 2026-09-13; capabilities 2026-09-13; coverage 2026-09-13.*

## What it is

cFIREsim — Crowdsourced Financial Independence and Retire Early Simulator — answers one question:
if you retired into the worst sequence of returns on record, would the money have lasted? You give
it a retirement year, an end year, a portfolio value and a yearly spend, and it replays that plan
against every overlapping historical window of that length. A 30-year plan entered today runs 127
cycles, 1871–1900 through 1997–2026, and "success" means the portfolio never touched zero. The
default inputs — $1,000,000, $40,000 a year, 75/25 — came back at 93.70%, with the failures
clustered on 1966 and 1969 starts.

The modelling underneath is deeper than the front page suggests. Allocation is split across
equities, bonds, gold and cash, with an annual fee percentage, optional annual rebalancing and a
glide path that walks you to a different target allocation between two years you pick. Eight
spending plans are offered: inflation-adjusted, not inflation-adjusted, percent of portfolio,
variable spending with a z-value, VPW, Hebeler Autopilot, Guyton-Klinger and variable CAPE — each
with an optional floor and ceiling on top. Inflation runs on historical CPI or a flat rate you set.
Two Social Security streams, pensions and up to eighty one-off or recurring income and expense
adjustments sit alongside, each with its own start year, end year and inflation treatment.

## Pricing

Free, with nothing to buy. There is no account, no login, no tier and no donation link anywhere on
the site. The only commercial presence is a banner for the author's newer product, FIREproof.

## Data & coverage

It ships no market data and makes no forecast. The historical series are Robert Shiller's monthly
S&P 500 dataset — prices, dividends, earnings, US CPI and the 10-year Treasury yield — running from
1871, plus gold prices from Kitco added in 2021. Cash is the exception: the author found no usable
historical series, so you supply a growth rate, defaulting to 0.25%. Everything is US.

Besides replaying all of history, the Data Method dropdown will restrict the run to a year range,
substitute a constant growth rate, or trace a single named cycle. An Investigation option solves
the other direction — the largest initial spend that still clears a success rate you choose.

## Integrations

None, and that is the design. There is no public API, no login and no saved scenarios. What leaves
the page is a CSV of every year of every cycle and a permalink that reloads your inputs, which is
the intended way to keep a scenario.

## Limitations

- **No taxes and no account types.** One pot of money, no Roth, no RMDs, no brackets. You are
  expected to bake tax into your spending number yourself.
- **The cycles are not independent trials.** 127 overlapping 30-year windows share most of their
  years; a 93.7% success rate is not a 93.7% probability. There is no Monte Carlo mode.
- **US data only.** Shiller's S&P 500, US CPI, US Treasuries. No international equity or bond series
  at any setting, and gold was flat for decades of the 1800s, which flatters gold-heavy allocations.
- **Nothing persists.** Lose the bookmark and you retype the form.
- **Closed source and feature-frozen.** The site's changelog ends in September 2022; the open
  repository is the 2.x JavaScript version whose last code commit was March 2016.

## Alternatives

FIRECalc is the older tool this one was built to improve on, with the same historical-cycle method
and a plainer interface. [Portfolio Visualizer](https://stockmarketstack.com/tools/portfolio-visualizer) covers similar ground with a Monte Carlo mode and
more asset classes. FIREproof, from the same author, is where the missing half lives — federal and
state tax, account types, RMDs and Roth conversions — free to try with a $10-a-month Pro tier, and
it is the reason cFIREsim itself is unlikely to gain those features.

## FAQ

### Is cFIREsim still maintained?

It runs, but it is frozen. A simulation submitted on 13 September 2026 returned normally, and the header reported market data through 1 August 2026. The changelog on the site's News page, however, stops at 9 September 2022, and the Internet Archive's capture of 18 July 2026 still showed the header advertising data through 1 November 2024 — so the automatic data refresh had stalled for roughly twenty months before someone reset it. Expect no new features.

### Does cFIREsim account for taxes?

No, in any form. It holds one undifferentiated pot of money with no notion of taxable, tax-deferred or Roth accounts, and no RMDs, brackets or capital-gains treatment. The site's own guidance is to gross up your Initial Yearly Spending by whatever you expect to owe.

### Can I get the results out of cFIREsim?

Yes. Every run produces a permalink that reloads the same inputs, and an Export to CSV link that returns a year-by-year row for every cycle — 24 columns covering spending, fees, each asset sleeve's growth and the ending portfolio in both nominal and real dollars. A default 30-year run exports about 4,000 rows.

### Is cFIREsim open source?

Not the version you use. The live 3.0 site is closed-source Python/Django. The Apache-2.0 repository cFIREsim-open is the abandoned 2.x JavaScript rewrite — its last code commit was in March 2016, its last commit of any kind in December 2020, and its README states plainly that cfiresim.com has been redone and is closed-source.

## Also from Lauren Boland

- [FIREproof](https://stockmarketstack.com/tools/fireproof.md)

## Also worth comparing

- [FI Calc](https://stockmarketstack.com/tools/ficalc.md) — Twelve withdrawal strategies replayed against every US market cycle since 1871.
- [Boldin](https://stockmarketstack.com/tools/boldin.md) — A year-by-year US retirement model — accounts, taxes, Social Security, Medicare, housing.
- [ProjectionLab](https://stockmarketstack.com/tools/projectionlab.md) — Model a whole financial life as milestones and cash flows, then run it against history.
- [Backtest by Curvo](https://stockmarketstack.com/tools/curvo.md) — Backtest a portfolio of European UCITS funds on index data reaching back to 1970.
- [Portfolio Charts](https://stockmarketstack.com/tools/portfolio-charts.md) — Any asset allocation, charted since 1970 in twelve countries' currencies and inflation.
- [Portfolio Visualizer](https://stockmarketstack.com/tools/portfolio-visualizer.md) — Backtest an asset mix to 1972, run Monte Carlo, regress it on Fama-French factors.