This post uses hypothetical scenarios for illustrative purposes only. It does not describe any actual client, transaction, or representation, and is not legal advice.
Picture a sale where the tax planning was done years ago, or so everyone believes. The company spent two decades as a C corporation, the owner’s accountant filed an S election a few years back to stop the double tax, and now a buyer has shown up with an asset purchase agreement — buyers of closely held companies almost always want assets. The owner expects a single layer of tax at capital gains rates, because that is the whole point of the S election. Then the deal accountant asks one question: what year did the S election take effect? If the answer is inside the last five years, a corporate-level tax everyone thought was dead comes back at 21%, on top of the shareholder-level tax, and the seller’s net proceeds just dropped by a number large enough to reprice the deal.
That is the built-in gains tax of Section 1374, and it exists precisely to police this pattern. Congress was not willing to let a C corporation facing a taxable asset sale elect S status on the way out the door and skip the corporate-level tax it had been deferring for decades. The statute’s answer is a recognition period: for five years after the S election takes effect, gain that was already baked into the company’s assets on the conversion date still gets taxed at the corporate level when recognized, as if the S election had never happened for that slice of gain. The full text is worth reading in the original at 26 U.S.C. § 1374; the mechanics below are all in there.
The tax reaches gain that existed on conversion day, and only that gain
Section 1374 is narrower than sellers fear and broader than they hope. The corporate-level tax — computed at the highest corporate rate under Section 11(b), currently 21% — applies to net recognized built-in gain: gain recognized during the recognition period on assets the corporation held on the first day of its first S year, but only up to the appreciation that existed on that day. Two ceilings do the limiting work. First, asset by asset, the recognized built-in gain on any disposition is capped at that asset’s value-over-basis spread as of conversion day — post-conversion appreciation is pure S-corporation gain, taxed once at the shareholder level like any other. Second, in the aggregate, the statute caps everything at the net unrealized built-in gain: the total spread between the fair market value and adjusted basis of the company’s assets measured on the first day of S status, netted against built-in losses. Once cumulative recognized built-in gains hit that ceiling, Section 1374 is spent, even inside the five years.
Both ceilings share a trigger date, which is why the single most valuable piece of paper in a former C corporation’s tax file is a valuation as of the S election’s effective date. The statute puts the burden on the corporation to establish that gain on a sold asset exceeds its conversion-day spread, or that it acquired the asset afterward. A company that converted with a contemporaneous appraisal can prove which gain is old and which is new; a company that converted on its accountant’s one-page election form and nothing else walks into the sale with the presumption running against it. For a business whose value sits in goodwill — which is most of them — the conversion-day valuation of that goodwill is the whole fight, because goodwill held on conversion day is an asset like any other, and the growth in it since conversion is the part the seller gets to keep at one layer of tax.
The statute also sweeps in items that don’t look like asset sales. Cash-method receivables collected after conversion, completed-contract income attributable to pre-conversion work — income items economically earned in the C years but taken into account in the S years are treated as recognized built-in gain when they land. The mirror rule treats pre-conversion liabilities deducted later as built-in losses, which helps.
The clock is five years, and you cannot outrun it with paper
The recognition period is the five-year span beginning on the first day of the first S year. It was ten years when the modern statute was written, bounced through temporary reductions after 2009, and settled at five permanently in the 2015 PATH Act. Five years is short enough to plan around, which is exactly what Congress understood: the statute contains anti-avoidance plumbing for the obvious moves. An installment sale doesn’t stretch past the clock — if the company sells an asset during the recognition period and collects on the note for years afterward, every payment is taxed under Section 1374 as if received in the year of sale. And assets that arrive from a C corporation with transferred basis — a merger of a C subsidiary into the S company, for instance — carry their own fresh recognition period measured from the day they arrived, so the five-year clock cannot be laundered through a reorganization.
What does work is time. A seller eleven months from the five-year line has one of the cleanest tax arguments for deal timing that exists, worth modeling before anyone signs a letter of intent. If the closing must happen inside the window, the structure conversation gets more interesting. A straight stock sale avoids Section 1374 entirely — no corporate-level asset disposition, no recognized built-in gain — but buyers give up the basis step-up and usually pay less for it, the tradeoff at the center of my post on what a 338(h)(10) election costs the founder. And the election that makes a stock sale taxable as an asset sale brings Section 1374 right back, because the deemed asset sale is a disposition like any other. The same interaction runs through F-reorganization structures, where the timing of the S election and the deemed transfers matters — mechanics I covered in the post on F-reorg rollover timing.
Softening the blow inside the window: C-year attributes survive for this one purpose. Net operating loss carryforwards from the C years, unusable against ordinary S-corporation income, are allowed as deductions against net recognized built-in gain, and C-year business credit carryforwards can offset the Section 1374 tax itself. A former C corporation with legacy NOLs may find the built-in gains tax substantially papered over by attributes it thought were stranded. And the corporate-level tax generally passes through to shareholders as a loss that offsets the gain flowing through to them, so the economic hit, while real, is not quite the headline 21% stacked naively on top.
The purchase agreement should know which side of the clock you’re on
For a Florida seller there is a second-order consequence: Florida has no personal income tax, but it does have a corporate income tax that piggybacks on federal treatment, and an S corporation generally owes Florida corporate tax for a year in which it owes federal tax at the corporate level. A built-in gains year is typically also a Florida filing year, a detail that surprises owners who haven’t filed a Florida corporate return since the S election. The deal documents should reflect all of this rather than discover it: the tax representations should state the S election date and its validity, the pre-closing tax covenant should allocate responsibility for the Section 1374 liability (it is legally the corporation’s tax, which in an asset deal means it is economically the seller’s through the entity the seller keeps), and the flow-of-funds math should account for it next to the shareholder-level tax — the same discipline as the distribution mechanics in my post on S corporation tax distribution covenants. Sellers straddling a year-end should also look at the closing-of-the-books election covered in the post on stub-period allocations, because which year the gain lands in determines whose return it lands on.
The five-year clock is the rare tax rule that rewards nothing but patience. Whether the right answer is waiting it out, restructuring around it, or pricing it into the deal is a math problem — but only for sellers who know the clock exists before the buyer’s accountants do.
If you are planning an asset sale of an S corporation that spent years as a C corporation, feel free to reach out to my firm manager, Magda, at Magda@montague.law, or fill out our contact form. Mention you read this post.
