William P. Bengen is a retired financial adviser who first articulated the 4% withdrawal rate ("Four percent rule") as a rule of thumb for withdrawal rates from retirement savings;[1] it is eponymously known as the "Bengen rule".[2] The rule was later further popularized by the Trinity study (1998), based on the same data and similar analysis. Bengen later called this rate the SAFEMAX rate, for "the maximum 'safe' historical withdrawal rate",[3] and later revised it to 4.5% if tax-free and 4.1% for taxable.[4] In low-inflation economic environments the rate may even be higher.[5][6][7]