BiggerPockets Money Podcast 120: Are FIRE Naysayers Bad at Math? Yes. with Michael Kitces
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Apr 13, 2020 
Michael Kitces, financial planner and researcher behind Nerd's Eye View, breaks down the 4% rule and safe withdrawal research. He explains historical worst-case sequences, why market drops are rarely catastrophic, bond and cash-bucket strategies, the retirement red zone, and practical levers like guardrails, modest spending tweaks, and side hustles to strengthen long-term plans.
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Origin Of The 4% Rule
- The 4% rule came from Bill Bengen's worst-case historical 30-year return analysis, not averages.
- He picked ~4.1% because it survived the worst retirement sequences in history, so it's a worst-case safety buffer.
Three Historical Drivers Of Safety
- Replications with broader datasets show three distinct historical periods (1907, 1929, 1966) that drive the ~4% floor.
- Diversification and dataset choices nudge the safe rate slightly but generally converge near 4–4.5%.
Average Versus Worst-Case Withdrawal Rates
- Average historical safe withdrawal rates are closer to 6–6.5%, but worst-case framing produced the 4% rule.
- Modern diversification (small caps, more bond types) likely raises safe rates toward 4.5–5% for many portfolios.