Trinity Study
The 1998 research that tested historical withdrawal rates and gave rise to the 4% rule.
The Trinity Study is a 1998 paper by three Trinity University professors that examined how various withdrawal rates and stock/bond mixes would have fared across historical 30-year retirement periods. It found that a 4% initial withdrawal, adjusted for inflation, survived the vast majority of historical periods — the foundation of the modern 4% rule.
Its influence on FIRE is hard to overstate, but so are its limits. The study used a 30-year horizon and U.S. historical returns, and it measured success as simply 'not running out,' not maintaining a particular balance. Early retirees planning for 40 to 50 years, or worried about a future that looks worse than the past, often treat its 4% figure as a ceiling and stress-test with lower rates.
This definition is general information to help you understand a term, not financial, tax, or legal advice. Figures that change year to year (limits, thresholds, rates) should be confirmed against current official sources. For guidance on your situation, a licensed fee-only fiduciary is the right next step.