Many of the online calculators have used 4% as a reasonable withdrawal rate for 30 year periods using Monte-carlo calculators. However, based on various rolling data periods of actual market returns for US equity markets, a 4% withdrawal rate will not sustain for 30 year periods in 30-40% cases (whatever be the asset allocation). At 5% withdrawal rate, the failure rate over 30 year periods increases to 40-55%. While at 3.5%, it falls to <10% unless one is in 100% bonds or 100% equities.