What Is the Trinity Study?

The Trinity Study is a famous research paper published in 1998 by three professors from Trinity University (Texas, USA).
It analyzed how long a retirement portfolio can last based on different withdrawal rates, time horizons, and stock–bond mixes.

This study is the foundation of the popular 4% Rule used in retirement planning.


What the Study Did?
Researchers examined U.S. market data from 1926 to 1995 to test:

• How much retirees can safely withdraw each year
• How portfolios perform over 15–30 years
• How different stock–bond combinations affect survival of savings
• They simulated thousands of scenarios involving bull markets, recessions, inflation, and crashes.

Key Findings
 

1. 4% is generally a “safe withdrawal rate” : A retiree withdrawing 4% initially and adjusting for inflation each year had a high chance of making their savings last 30 years.
2. Higher stock allocation performs better long-term : Portfolios with 50–75% stocks showed the highest success rates.

3. Withdrawal rates above 6% are risky : Savings often ran out before 30 years if withdrawals exceeded 6%.


Why the Trinity Study Is Important?
It created a scientific basis for retirement planning by answering:

• “How much can I withdraw each year without running out of money?”
• Financial planners, FIRE (Financial Independence Retire Early) communities, and retirees still rely on it today.