I keep my returns forever, but discard the supporting documents after five years.
I have all records since 1991…Why?…they came in handy when I was going through the Fed security clearance process, ( try filling out Fed form 86 without records) when that FBI agent agent finally got around to interviewing me at my home, I had more supporting evidence of my history than he did….and he had a whole briefcase full…not so with my past wife…it was put on hold until her parents could be interviewed at a US Embassy 6,000 miles away.