---
title: "Safe Withdrawal Rate Research Reference"
description: "Summary table of major safe withdrawal rate studies including the 4% rule and subsequent research showing updated SWR ranges by time horizon."
canonical: https://www.getswoopr.com/tables/portfolio/safe-withdrawal-rate-research-reference/
source: "Swoopr Investment: https://www.getswoopr.com"
---

## Direct Answer



> The original "4% rule" from the 1994 Bengen study found a 4% initial withdrawal rate (adjusted for inflation annually) succeeded over all 30-year periods from 1926 to 1994 for a 50/50 stock/bond portfolio. Subsequent research and lower bond yields have led many planners to suggest 3.3-3.7% for new retirees.







# Safe Withdrawal Rate Research Reference



By [Swoopr Editorial Team](https://www.getswoopr.com/authors/swoopr-editorial-team/) · Published September 17, 2026 · *AI-assisted research, editorially reviewed.*





## Key Safe Withdrawal Rate Research Findings



| Study | Year | Portfolio | Time Horizon | SWR Found | Notes |
| --- | --- | --- | --- | --- | --- |
| Bengen (original) | 1994 | 50% stocks / 50% bonds | 30 years | 4.0% | SAFEMAX from 1926-1994 data |
| Trinity Study | 1998 | 50/50 to 75/25 | 15-30 years | 4.0-4.5% | 95% success on 30-yr periods |
| Bengen (updated) | 2006 | 60/30/10 (add small-cap) | 30 years | 4.5% | Small-cap tilt increases SWR |
| Pfau (low-yield env.) | 2012 | 60/40 | 30 years | 3.3-3.7% | Post-2008 low rate environment |
| Kitces (floor) | 2012 | 60/40 | 30 years | 4.5%+ | Rising equity glide path thesis |
| ERN Research | 2018 | 60/40 | 30-60 years | 3.25-3.5% | Early retirees need lower rates |
| Morningstar (2021) | 2021 | 60/40 | 30 years | 3.3% | Low starting bond yields |
| Morningstar (2024) | 2024 | 60/40 | 30 years | 3.7-3.8% | Higher starting bond yields |



Source: Published academic and practitioner research papers cited in References below. Data through 2024; last checked September 2026.







## Frequently Asked Questions


### What is the 4% safe withdrawal rule?

The 4% rule states that a retiree can withdraw 4% of their initial portfolio in year one, then increase that dollar amount by inflation each year, with very high probability of not running out of money over 30 years. It was derived from William Bengen's 1994 analysis of U.S. historical returns from 1926 to 1994.


### Is the 4% rule still valid?

Debate continues. At today's higher stock valuations and historically low real bond yields (before 2022), many researchers recommended 3.3-3.5%. After 2022's bond yield normalization, Morningstar's 2024 estimate was 3.7-3.8%. The 4% figure remains a reasonable starting point for planning but should be stress-tested against current conditions.


### How long should my retirement planning horizon be?

Plan for at least 30 years, and for couples or early retirees, 40+ years. The probability that one member of a 65-year-old couple lives to age 90 is over 50%. Early retirees (retiring at 55) should model 40-50 year horizons, which substantially lowers safe withdrawal rates.







## Cite This Page



If you reference this table in your own work, use the following citation format and add the date you accessed it:



> Swoopr Editorial Team. (2026). *Safe Withdrawal Rate Research Reference*. Swoopr Investment. [https://www.getswoopr.com/tables/portfolio/safe-withdrawal-rate-research-reference/](https://www.getswoopr.com/tables/portfolio/safe-withdrawal-rate-research-reference/)



Check the figures against the primary sources listed under References before you rely on or republish them; the series they come from are revised.







## References



- [Financial Planning Association: Journal of Financial Planning (Bengen 1994)](https://www.financialplanningassociation.org/)
- [AAII: Trinity Study (Cooley, Hubbard, Walz 1998)](https://www.aaii.com/)
- [Morningstar: Safe Withdrawal Rate Research](https://www.morningstar.com/)