In order to convert from a SMLLC to a S Corp, all one has to do is file form 2553 before March 15th to elect S Corp status for that particular year. IRS will send an acceptance letter stating the SMLLC is now an S Corp for tax purposes and must file a form 1120S by March 15th of the following year. However, there are limitations on when the election can take effect. Specifically, your S corp tax status must become effective within the 75-day period before you file the form or within 12 months after you file it You do NOT need a new EIN to convert your SMLLC to an S Corp. Bank accounts, company name, etc. will stay the same because it's the same legal entity.