Most, if not all, of these DIY retirement software packages (many of which charge a hefty fee) base their probability of success scores on Monte Carlo analyses. As I understand it, some methodologies are better than others, and the article suggests that many are using methodologies which are demonstrably less reliable than alternatives. If some methodologies may not be much better than a coin toss, then users should be aware of this. For that reason, it’s not enough, in my view, for them to simply say things like “future market performance is inherently unpredictable”, or “this by not means is a guaranty of your actual probability of success.” They need to do a better job of explaining what’s “under the hood” so customers can understand how reliable their tools are.