Safe Withdrawal Rate Calculator

How the safe withdrawal rate calculator works

This calculator shows how much annual income your portfolio can sustain at a given withdrawal rate, along with a success probability — the historical likelihood that your money would have lasted through your entire retirement.

What is the Trinity Study?

The Trinity Study is a 1998 paper by three Trinity University finance professors — Philip L. Cooley, Carl M. Hubbard, and Daniel T. Walz — that tested how often various withdrawal rates would have lasted through 30-year retirements using U.S. stock and bond returns starting in 1926. They found that a 4% initial withdrawal, adjusted upward for inflation each year, succeeded in 95% of historical 30-year periods for portfolios with at least 50% in stocks. The study was updated in 2011 and remains the most widely cited research behind the 4% rule.

The 4% rule and 30-year retirements

The Trinity Study assumes a fixed 30-year retirement window. You withdraw 4% of the portfolio in year one, then adjust the dollar amount upward by inflation each subsequent year regardless of market performance. The 30-year horizon matters: success rates for the 4% rule drop sharply for 40-year and 50-year retirements, which is why early retirees often target a 3.25–3.5% rate to add a safety margin.

Bengen's original 1994 research

Financial advisor William P. Bengen first proposed the 4% rule in his 1994 paper “Determining Withdrawal Rates Using Historical Data,” using the same overlapping-period methodology that the Trinity professors later validated. Bengen's paper introduced the concept of “SAFEMAX” — the highest withdrawal rate that survived every historical retirement period in his data set — and concluded that 4.15% met that bar. Both studies are typically cited together as the foundation for the 4% rule.

Asset allocation: 50–75% stocks

Too little in stocks and inflation erodes your purchasing power. Too much and a bad early sequence of returns can deplete the portfolio. Historical data suggests 50–75% stocks is the sweet spot for 30-year retirements. Bond-heavy portfolios (under 40% stocks) actually had lower 30-year success rates because they couldn't outpace inflation over long periods.

Does the 4% rule still hold today?

Researchers including Michael Kitces, Wade Pfau, and Morningstar's Christine Benz have argued that elevated U.S. equity valuations and lower expected bond returns may justify a more conservative starting rate — typically 3.3% to 3.7% — for retirements beginning today. Bengen himself revised his estimate upward to 4.7% in a 2020 paper after refining the original methodology and adding more historical data. The calculator lets you test any rate against the historical success framework.

Adjustable vs fixed withdrawal

The original Trinity Study uses a fixed inflation-adjusted withdrawal: take 4% in year one, then increase the dollar amount by inflation regardless of how the market performs. Guardrails strategies (cut spending after bad years, increase after good ones) can significantly improve success rates and often allow higher initial withdrawals — a different methodology with different tradeoffs.