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cFIREsim

cFIREsim

Money & Personal Finance ResourcesInvestment & Portfolio ToolsFinancial CalculatorsRetirement Planning
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Verified working Sep 20, 2026

Stress-test retirement spending against long-run market history.

cFIREsim is a web-based retirement simulator for testing withdrawal plans against historical market and inflation data. Users can model portfolio size, spending rules, asset allocation, Social Security or pension income, glide paths, and other cash-flow adjustments to estimate how often a plan would have lasted.

Why it stands out

  • Built specifically around FIRE-style withdrawal testing rather than general budgeting.
  • Includes several advanced spending rules that many simple retirement calculators omit.
  • Lets users add detailed cash-flow adjustments such as pensions, Social Security, freezes, and recurring expenses.
  • Supports allocation glide paths and fee assumptions, making sequence-of-returns testing more flexible.
  • Shows current data freshness and a large public count of simulations run.

Good to know

  • The site explicitly frames results as educational, not personalized financial advice.
  • Historical simulations can show how a plan would have handled past markets, but they do not predict future returns.
  • More advanced modeling such as tax-aware projections, real estate, ACA optimization, and Roth conversions is presented as part of the separate FIREproof product.
  • Enabling investigation options may increase simulation time.

Under the radar: Use separate simulation tabs to keep a baseline plan open while changing only one variable at a time, such as withdrawal method or equity allocation, so the output differences are easier to interpret.

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Illustration for cFIREsim