How simpleFIRE calculates, where its data comes from, and who makes it.
Methods
Fixed rate
One result: your money grows at the same annual return every year. Inflation follows your setting.
Monte Carlo
5,000 random markets. Each year's return is drawn at random, with the average and volatility of your stock and bond mix. Inflation follows your setting.
Historical
Every start year since 1928, with that period's actual returns and actual inflation, as in the Trinity Study.
Chance
The share of scenarios or historical periods in which your plan works: your portfolio lasts or you reach your target.
Assumptions
Withdrawals
Rise with inflation at every payment. Paid at the end of each period by default, as in the Trinity Study.
Compounding
Fixed rate and Monte Carlo add returns as often as your Compounding setting says. Historical uses each year's actual return.
Rebalancing
Monte Carlo and Historical restore your stock and bond mix once a year.
Taxes & Fees
Not included: results are before taxes, commissions and fund fees.
Data 1928–2025
Stocks
S&P 500 with dividends. Aswath Damodaran, NYU Stern.
Bonds
10-year US Treasury, return computed from Federal Reserve yields. Aswath Damodaran, NYU Stern.
Inflation
US consumer prices (CPI-U), December to December. U.S. Bureau of Labor Statistics, via FRED.
Checked Against Research
Trinity Study & Bengen
On the data these studies used, the Historical method matches their published results: the Trinity Study (Cooley, Hubbard & Walz, 1998) and Bengen (1994).
Our Data
Longer, newer and open: 98 years through 2025, including the 2000 and 2008 crashes and the 2022 inflation, from public sources anyone can check, updated every year. The studies used a paid database, now discontinued, ending in 1995 (Trinity Study) and 1992 (Bengen).
Your Results
Bonds here are 10-year US Treasuries, backed by the US government, rather than the Trinity Study's corporate bonds. Your results can differ from the published tables by a few percentage points, usually on the cautious side.
Author
Dawid Milczarek
simpleFIRE is not affiliated with S&P Dow Jones Indices, the authors or the data providers above.