{"version":"2026-retirement-methodology-disagreement","name":"SwitchWize Retirement Calculator Methodology Disagreement Benchmark","snapshotDate":"2026-08-12","citeAs":"SwitchWize, \"Retirement Calculator Methodology Disagreement Benchmark.\" Retrieved 2026.","sourcePage":"https://www.switchwize.com/calculators/retirement-methodology-comparison","headline":{"scenario":"55-year-old catching up: $500,000 saved, $30,000 first-year withdrawal (6% rate), 30-year horizon, 60/40 stock-bond mix","deterministicResult":"Shows 100% safe -- projects the plan ending with $1,517,813 after 30 years, assuming a flat 9.0% return every single year","historicalBacktestSuccessRate":0.87,"historicalBacktestFailedYears":[1928,1929,1930,1931,1936,1937,1962,1965,1966],"historicalBacktestFailedCount":9,"historicalBacktestTotalYears":69,"monteCarloApproxSuccessRate":0.71,"monteCarloTrials":20000,"realHistoricalFailureRateTheCalculatorShowsAsZero":0.13},"allScenariosTested":[{"name":"Standard 30-year retiree, 60/40, 4% rule","withdrawalRate":0.04,"deterministicSurvives":true,"historicalBacktestSuccessRate":0.971,"historicalBacktestFailedYears":[1929,1930]},{"name":"55-year-old catching up, 6% withdrawal rate","withdrawalRate":0.06,"deterministicSurvives":true,"historicalBacktestSuccessRate":0.87,"historicalBacktestFailedYears":[1928,1929,1930,1931,1936,1937,1962,1965,1966]},{"name":"Early retiree / FIRE, 40-year horizon, 25x/4%","withdrawalRate":0.04,"deterministicSurvives":true,"historicalBacktestSuccessRate":0.966,"historicalBacktestFailedYears":[1929,1930]},{"name":"Conservative 40/60 allocation, 3.5% withdrawal","withdrawalRate":0.035,"deterministicSurvives":true,"historicalBacktestSuccessRate":1,"historicalBacktestFailedYears":[]},{"name":"Aggressive withdrawal, 5% rate","withdrawalRate":0.05,"deterministicSurvives":true,"historicalBacktestSuccessRate":0.942,"historicalBacktestFailedYears":[1928,1929,1930,1931]}],"keyFinding":"Across all five representative scenarios tested, the fixed-rate deterministic method (the methodology used by NerdWallet and SmartAsset's free calculators) showed 100% of plans succeeding -- zero exceptions. Testing the same exact plans against every real 30-to-40-year period of actual U.S. market history since 1928 found real historical failure rates ranging from 0% to 13%, a risk entirely invisible to the fixed-rate method.","sources":[{"label":"SwitchWize retirement simulation engine","detail":"Client-side Monte Carlo (2,000-20,000 trial bootstrap resample) and historical backtest (every real consecutive market period), both drawn from the same 1928-2025 annual S&P 500 total return + 10-year Treasury dataset.","url":"https://www.switchwize.com/calculators/retirement-methodology-comparison"},{"label":"Historical returns dataset","detail":"Annual S&P 500 total return (with dividends) and 10-year Treasury total return, 1928-2025.","url":"https://pages.stern.nyu.edu/~adamodar/New_Home_Page/datafile/histretSP.html"}],"methodology":{"summary":"Five representative retirement scenarios (varying withdrawal rate, horizon, and stock allocation) were each run through three methods sharing the same underlying historical dataset: a fixed-rate deterministic projection, a Monte Carlo simulation, and a historical backtest against every real consecutive market period available.","caveat":"Education-only estimate based on past market history; past returns do not guarantee future results. Excludes taxes, fees, Social Security, and healthcare costs. Monte Carlo figures carry natural sampling variance and are published as approximate; historical-backtest figures are exact and reproducible."}}