Converting an existing C-corp to an S-corp is a real, common move once double taxation stops making sense for the business – but the conversion doesn’t wipe the slate clean on gains the corporation already built up while it was a C-corp. Section 1374’s built-in gains (BIG) tax exists specifically to stop businesses from converting right before a sale purely to dodge corporate-level tax on appreciation that happened under C-corp status.
What Counts as a Built-In Gain
A built-in gain is the difference between an asset’s fair market value and its tax basis on the exact day the S-corp election takes effect. A building worth $2 million with a $500,000 basis on conversion day carries a $1.5 million built-in gain – and that $1.5 million stays exposed to corporate-level tax if the asset gets sold within the recognition window, even though the corporation is now taxed as an S-corp for everything else.
The Five-Year Recognition Period
The BIG tax applies if a converted S-corp sells an asset carrying built-in gain within five years of the conversion date. A C-corp that converts on January 1, 2026 has its recognition period run through December 31, 2030 – sell the asset on day one of year six, and the built-in gains tax no longer applies to that sale, only ordinary S-corp pass-through taxation does.
The Tax Rate Is the Corporate Rate, Applied First
Gains that fall inside the recognition window get taxed at the flat 21% corporate rate at the entity level, before anything passes through to shareholders on their K-1s – meaning the same appreciated asset can effectively face two layers of tax during the window (the 21% BIG tax at the corporate level, then ordinary income tax on the shareholder’s own return), which is exactly the double-taxation outcome the S-corp election was supposed to avoid.
Why This Catches Businesses That Convert Right Before a Sale
The recognition period exists specifically to prevent a business from converting from C-corp to S-corp shortly before selling a highly appreciated asset just to avoid the corporate-level tax that would apply under continued C-corp status. A business planning any kind of exit or major asset sale needs to model out whether that sale falls inside or outside the five-year window before assuming the S-corp election alone solves its double-taxation problem.
Only Pre-Conversion Appreciation Is Exposed
The BIG tax only applies to the gain that existed on the conversion date – appreciation that happens after the S-election takes effect is taxed under normal S-corp pass-through rules with no BIG tax exposure at all. This means the real planning question is quantifying exactly how much of any eventual gain is pre-conversion built-in gain versus post-conversion appreciation, not treating the whole sale as automatically subject to the five-year rule.
Affiliate Disclosure: This page may contain affiliate links. If you make a purchase or sign up through these links, we may earn a commission at no extra cost to you.
Related reading: C-Corp Double Taxation: How It Actually Works and When to Elect S-Corp Status.
Recent Comments