FIRE Calculator: Test Your Retirement Plan Against 150 Years of Market History

What Is FIRE?

FIRE stands for Financial Independence, Retire Early. The idea is straightforward: save aggressively, invest in low-cost index funds, and build a portfolio large enough to cover your living expenses indefinitely. Most FIRE practitioners target a portfolio of 25× to 33× their annual spending—corresponding to a 3–4% annual withdrawal rate—which historically has been enough to sustain a multi-decade retirement.

This calculator lets you test whether a specific portfolio and spending level would have survived every historical market environment since 1871. Rather than guessing at future returns, it uses real data to show how your plan holds up under the best and worst conditions the U.S. economy has actually produced.

How This Calculator Works

The calculator uses a method called rolling-period backtesting. It takes your inputs—portfolio size, annual spending, asset allocation, and retirement length—and simulates your retirement starting in every year from 1871 through the most recent available data. Each simulation uses the actual stock returns, bond yields, and inflation for that specific historical period. The result is a success rate: the percentage of all historical starting years where your money lasted the full retirement.

The underlying data comes from Robert Shiller’s dataset at Yale University, which is widely used in academic finance. It includes S&P 500 total returns (with dividends reinvested), 10-year U.S. government bond yields, and Consumer Price Index (CPI) inflation. A 95% or higher success rate is generally considered a robust plan, though no historical backtest can guarantee future results.

Most retirement calculators ask you to guess your future returns. This one does not. Instead, it takes your retirement plan and tests it against every historical period in the U.S. stock and bond markets going back to 1871. If you had retired in 1929, would your money have lasted? What about 1966, or 2000? This calculator answers those questions using actual market data.

The approach is called historical backtesting, and it was popularized by the Trinity Study and tools like FIRECalc. Rather than using a single average return (which hides the enormous variation in real-world outcomes), it runs your plan through every possible starting year and shows you how many of those scenarios succeeded. A plan that survived 95% or more of historical periods is generally considered robust.

The data behind this calculator comes from Robert Shiller’s dataset at Yale, which tracks S&P 500 total returns (including dividends), long-term U.S. government bond yields, and actual CPI inflation. The dataset covers 154 years of market history—including the Great Depression, stagflation, the dot-com crash, and the 2008 financial crisis.

How to Interpret Your Results

The success rate is the percentage of historical starting years where your portfolio lasted the full retirement term without running out. A 95% success rate means that in 95% of all historical periods tested, your money would have survived. The remaining 5% represent the worst-case scenarios—typically periods that started with a severe bear market followed by high inflation, like the early 1960s or mid-1970s.

The portfolio paths chart shows every tested cycle overlaid on a single graph. Blue lines represent cycles where the portfolio survived; red lines are the failures. The spread between lines gives you a visual sense of the range of outcomes. Notice how some paths soar to many multiples of the starting balance while others decline steadily—this is the reality of sequence-of-returns risk.

A few rules of thumb for interpreting the success rate:

• 95% or higher — Your plan is historically very robust. This is the threshold most FIRE planners aim for.
• 80–94% — Workable, but you should have a backup plan: the ability to cut spending, earn some income, or delay retirement by a year or two.
• Below 75% — The plan has a meaningful chance of failure. Consider reducing spending, increasing your portfolio, or shortening the time horizon.

Limitations

Historical backtesting is one of the best tools available for retirement planning, but it is not a crystal ball. Keep these caveats in mind:

• No taxes. This calculator does not account for income taxes on withdrawals. In practice, withdrawals from traditional 401(k) and IRA accounts are taxed as ordinary income. Your actual spending power may be 15% to 25% lower than what the calculator shows, depending on your tax bracket and account types.
• U.S.-only data. The historical returns are based on U.S. stocks and bonds. The United States had an unusually strong 20th century—many other developed countries experienced lower real returns, wars, and currency crises that would have worsened retirement outcomes. International diversification is important but not captured here.
• Past performance. The fact that a 4% withdrawal rate survived every historical 30-year period does not guarantee it will survive the next one. Future returns could be lower than any past period, particularly if current stock valuations are elevated.
• Static allocation. This calculator assumes a fixed stock/bond split throughout retirement. In practice, many retirees adjust their allocation over time (a glide path), and some use bucket strategies or dynamic withdrawal rules.
• No spending flexibility. In real life, most people cut spending during downturns. The “percentage of portfolio” spending model captures some of this, but real-world behavior is more nuanced.

Data Sources and Methodology

All simulations are powered by Robert Shiller’s publicly available dataset, maintained at Yale University and widely used in academic finance research. The calculator uses the following data series, covering 154 years from 1871 through 2024:

• Stock returns: S&P 500 total returns, including reinvested dividends. These represent the broad U.S. equity market.
• Bond yields: 10-year U.S. government bond yields (GS10), used as the fixed-income return for the bond portion of the portfolio.
• Inflation: Consumer Price Index (CPI) data, used to adjust spending for inflation in the “constant” spending model.
• Methodology: Rolling-period backtesting. For a 30-year retirement, the calculator tests every possible 30-year window (1871–1900, 1872–1901, …, 1995–2024) and reports the percentage that survived without running out of money.

API Access

This calculator is also available as a free JSON API. You can query it programmatically to backtest retirement plans or find safe spending levels. For example: GET https://trueadvisor.com/api/fire-calculator/?portfolio=1000000&annual_spending=40000. Full parameter documentation is available at /llms.txt and the OpenAPI spec.