The Trinity study, as a question

What Cooley, Hubbard and Walz actually asked in 1998, what a 4% / 30-year success rate is and is not, and how to run the same kind of question on your numbers.

The question they asked

Cooley, Hubbard and Walz (1998), often called the Trinity study, asked how often a fixed initial withdrawal lasted 30 years on overlapping historical windows, for a few stock/bond mixes. A 4% initial rate on a stock-heavy mix lasted in most of those windows. That is a historical success table. It is not a probability that your retirement lasts, and it is not a 50-year result.

What we did not reprint

The Trinity study calculator asks the same kind of question on 1,000 seeded paths you can edit. It is not their tables. If you want the paper Killion actually ran — 5,000 regime-switching lifetimes, flexible versus rigid 4% — that is is the 4% rule still safe. If you want the rate to move with age, that is withdrawal rates by age.

How to use a success table

Compare two rates on the same engine. Do not take a 95% from 1998, a 92% from a blog, and a 88% from this site and average them. Different samples, different inflation treatments, different failure definitions. The reading-Monte-Carlo guide is the hygiene.

Frequently asked questions

What did the Trinity study measure?
How often a fixed initial withdrawal rate lasted 30 years on overlapping historical windows, for a handful of stock/bond mixes. It is a historical success table, not a forecast.
Is a Trinity study calculator the 1998 paper?
No. Ours asks the same kind of question on 1,000 seeded paths. The 4% research post is the paper Killion actually ran.