TurboTax is incapable of calculating the maximum permissible elective deferral to a self-employed 401(k) when you have made elective deferrals or Roth contributions to another employers qualified retirement plan in the same year. You must not mark the Maximize box and instead calculate the amount of the elective deferral limit that remains, explicitly enter that value as your elective deferral, then use the Maximize function for a SEP contribution or a Keogh Profit Sharing contribution to calculate the maximum permissible employer contribution.
