Educational tool. Not financial advice. Sources & methodology

Methodology & Data Sources

Every calculator on this site uses publicly available data and documented assumptions. This page explains where the numbers come from, what we assume, and where the limitations are.

Default assumptions

7% real return — the historical average real (inflation-adjusted) return of the S&P 500 over rolling 30-year periods. Source: SEC investor.gov. This is a planning assumption, not a prediction.

3% inflation — the long-term historical average. Actual inflation varies year to year. The 7% real return already accounts for this.

4% withdrawal rate — the initial safe withdrawal rate from the Trinity Study and Bengen’s original 1994 research, based on worst-case 30-year historical sequences. All are adjustable in every calculator.

Market return data

Historical S&P 500 return data is sourced from SEC investor.gov and Robert Shiller’s publicly available dataset. We use real (inflation-adjusted) returns as the default because they represent actual purchasing power growth. Nominal returns (before inflation) are available as an override in each calculator.

Withdrawal rate research

Bengen (1994) — William Bengen’s original research established the 4% rule: a retiree withdrawing 4% of their portfolio in year one, adjusted for inflation each subsequent year, would not have run out of money in any 30-year historical period since 1926.

Trinity Study (1998, updated 2011, 2016) — expanded Bengen’s work across different stock/bond allocations and time periods. Confirmed 4% as sustainable for 30-year horizons with at least 50% equities.

Kitces variable withdrawal research — Michael Kitces has published extensively on dynamic withdrawal strategies that adjust spending based on portfolio performance, potentially allowing higher initial rates with guardrails.

Dividend ETF yield data

Yields are reported as trailing 12-month distribution yield from fund prospectuses. Yield is not guaranteed income — it fluctuates with market conditions and fund management decisions. Net investment income tax (3.8% for high earners) and qualified dividend tax treatment are noted where relevant but not modeled in calculators by default.

Cost of living / geo-arbitrage data

Cost of living indices are sourced from Numbeo and Teleport. These are crowd-sourced and index-based — they capture general cost differences between cities but do not reflect individual spending patterns, housing choices, or lifestyle preferences. Use as directional guidance, not precise budgeting.

When calculations are approximate

Always. Every calculator produces estimates, not guarantees. Investment returns are inherently uncertain. Tax rules change. Cost of living data ages. Withdrawal rate research is based on historical data that may not predict future outcomes. Each calculator includes an inline methodology note describing its specific assumptions.

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