4% is 40K a year (before capital gains taxes). You could definitely live off of it on your own, but not super comfortably and definitely no family. I see a couple of options. I'd probably throw it into savings and build up a few years more years of engineering experience. Then I'd go part time as a consultant. If I could pull 90K a year at 20hours a week with somewhat reduced taxes, that'd be pretty sweet. Alternatively, I could just keep working normally as is until ~30 or so. By then I'd likely be looking at 2-2.5mil, which is definitely enough for me to retire with.