September 15 is the extended deadline for calendar year S corporations and partnerships. Which means this is the month people discover things. Here is one that comes up more than it should. The situation A two owner service company. Formed as an LLC in early 2024. Their lawyer told them to be an S corporation, their bookkeeper set up payroll, they ran W-2 wages for both owners, they filed a Form 1120-S for 2024 and another for 2025, and both years the K-1s flowed to their 1040s. New client walks in this September. I ask for the acceptance letter. Nobody has one. I pull the account. The IRS has no S election on file. Form 2553 was never sent. It was on the lawyer's checklist, the bookkeeper assumed the lawyer did it, the lawyer assumed the accountant did it. What they actually were A two member LLC with no election is a partnership. So for two years they filed the wrong return, on the wrong form, with the wrong owner compensation treatment, and paid payroll tax on wages that a partnership does not pay to its partners. Left alone this ends badly. The 1120-S filings get treated as unfiled 1120-S returns from an ineligible filer, the partnership returns were never filed at all, and the late filing penalty for a partnership return is $255 per partner per month for returns filed in 2026 and $260 for returns filed in 2027. Two partners, two years, twelve months capped. The exposure runs past $12,000 in penalties before anybody talks about tax. The fix Rev. Proc. 2013-30. It is the most useful revenue procedure a small practice can know, and it is not complicated. - It gives simplified relief for a late S election when the request is made within 3 years and 75 days of the intended effective date. They were inside that window by a comfortable margin. - The entity has to have intended to be an S corporation from that date, and has to have reported consistently as one. They had. Two 1120-S returns, two sets of K-1s, W-2 wages for both owners. Every piece of paper said S corporation. - It needs reasonable cause stated in the request. Not an excuse. A short factual explanation of what happened and why. - The Form 2553 gets filed with FILED PURSUANT TO REV. PROC. 2013-30 written across the top, with the statement of reasonable cause attached and every shareholder signing.