Trinity Study

The Trinity Study is a landmark 1998 academic paper titled 'Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable' by three finance professors at Trinity University (Philip Cooley, Carl Hubbard, and Daniel Walz). It is the empirical foundation of the 4% rule used in FIRE planning.

The study analyzed historical US stock and bond market data from 1926 to 1995 using rolling 30-year periods. It tested various portfolio allocations (stocks/bonds ratios) and withdrawal rates to determine which combinations allowed retirement savings to survive 30 years. The key finding: a 4% initial withdrawal rate (adjusted annually for inflation) had a 95%+ success rate for portfolios with 50-75% stock allocation over 30-year periods.

The study has been updated multiple times since 1998 with newer data, and findings have generally been confirmed. Critics note it was based on US data, does not account for taxes, and was designed for 30-year retirements — making 3-3.5% more appropriate for FIRE's longer time horizons.