What is the Trinity Study and what does it say about retirement withdrawals?
The Trinity Study (1998) analyzed historical U.S. market data and found that a 4% annual withdrawal rate from a diversified portfolio succeeded in over 95% of 30-year retirement periods. It is the foundational research behind the 4% rule used in retirement and FIRE planning.
Formula
Annual Safe Withdrawal = Portfolio Value × 0.04 (4%); Inverse: Required Portfolio = Annual Spending ÷ 0.04
Example
A retiree with $1,000,000 in a 60/40 stock-bond portfolio can withdraw $40,000 in year one, then adjust that amount for inflation each subsequent year. Historically, this portfolio survived all 30-year periods in the Trinity Study data roughly 95% of the time.
How it works in detail
The Trinity Study, formally titled 'Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable,' was published in 1998 by three finance professors at Trinity University: Philip Cooley, Carl Hubbard, and Daniel Walz. Using historical U.S. stock and bond return data from 1926 to 1995, they tested various withdrawal rates against every rolling 30-year retirement window to measure portfolio survival rates. Their headline finding: a 4% inflation-adjusted annual withdrawal from a portfolio holding roughly 50–75% stocks succeeded in approximately 95–98% of historical 30-year periods. At a 5% withdrawal rate, success rates dropped to around 80%, while 3% was nearly bulletproof. The study was updated in 2011 to include data through 2009, including the dot-com crash and 2008 financial crisis. The 4% rule held up, though some researchers—including Wade Pfau and Michael Kitces—note that today's lower bond yields and high equity valuations may reduce future success rates slightly, suggesting 3.3%–3.5% as a more conservative baseline for new retirees. For early retirees planning 40–50 year horizons, most FIRE practitioners apply the 4% rule cautiously or shade toward 3.5%.
Use Rightmont's FIRE calculator to apply the Trinity Study's 4% rule to your own numbers and see exactly when you can retire.
Open Free Calculator →Related Questions
How much do I need to retire?
Multiply your annual spending by 25. If you spend $60,000/year, you need $1,500,000. This is the 4% rule from the Trinity Study (1998) — withdraw 4% annually with a 95%+ historical success rate over 30 years.
What is the 4% rule for retirement?
The 4% rule says you can withdraw 4% of your portfolio in year one of retirement, adjust for inflation each year, and have a 95%+ probability your money lasts 30 years. It comes from William Bengen's 1994 research, later confirmed by the Trinity Study (1998).
What is a safe withdrawal rate for early retirement (40+ years)?
For retirements lasting 40+ years, research suggests 3.25–3.5% is safer than the traditional 4%. A $2M portfolio at 3.5% provides $70,000/year. With dynamic spending (cutting 10–15% in down markets), you can safely withdraw 4–4.5% even over 50 years.
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