For Bill and Melinda Gates, who announced on monday that they would be divorcing, a change in the step-up rule might be less costly. The Gates fortune, valued at $145.8 billion, is older, and they’ve already sold or donated much of their stake in microsoft Corp. But $26 billion of microsoft shares remain, and it isn’t clear how the couple will manage their assets in a split. A version of Biden’s plan was floated by President barack obama in 2015, but it died in a Republican-controlled Congress.