There are currently claims that between 30% and 70% percent of lottery winners will go bankrupt.
Indeed, the Certified Financial Planner Board of Standards says nearly a third of lottery winners declare bankruptcy—meaning they were worse off than before they became rich. Source: Fortune, By RIC EDELMAN January 15, 2016
In fact, about 70 percent of people who win a lottery or get a big windfall actually end up broke in a few years, according to the National Endowment for Financial Education. Source: Clevland.com Jan 14, 2016
There is a much older Skeptics post saying it is around 1% Are people who win the lottery more likely to go bankrupt? (I think, not sure I followed the answer) but it mentions lack of studies. Based on current reports there is now evidence available and/or the current claims are without foundation.
What is the Real Risk of Bankruptcy after a Lottery Win?
Does current research support current reported percentages?