Small employers hoping to set up a new SIMPLE IRA, SIMPLE 401(k) or a safe harbor 401(k) have until Oct. 1 to do so. SEP IRAs must be set up by Oct. 15 — if that’s when the taxpayer is filing his return. Solo 401(k) plans need to be set up by Dec. 31. If you are unable to follow the link, please click here for a PDF Version.