In this framework, if you have a floor income, your utility is negative infinity below that, and 0 at or above that income. So basically run the same analysis

In this framework, if you have a floor income, your utility is negative infinity below that, and 0 at or above that income. So basically run the same analysis with that utility function which is the CRRA function as risk aversion parameter gamma approaches infinity. Alternatively, read Bengen's 1994 article - using historical data at that time, the number he came up with was 4% and a 50/50 stock/bond portfolio - http://www.retailinvestor.org/pdf/Bengen1.pdf http://www.retailinvestor.org/pdf/Bengen1.pdf If you wanted to, you could segment your plan into a 'safe' withdrawal portfolio that puts a floor on your retirement income (assuming future is no worse than the past, which is of course not guaranteed), and one that maximizes spending/certainty-equivalent spending for some level of risk aversion.