S Corp Built-In Gains Tax: When a Converted C Corp Pays It

S Corp Built-In Gains Tax: When a Converted C Corp Pays It

An S corporation is supposed to avoid corporate-level income tax. Not always. If your company used to be a C corporation, the S corp built-in gains tax can apply when it sells assets that had already appreciated on the day it converted. The corporation pays it.

This piece covers who owes it, how long it lasts, and what to settle before a sale. Iota Finance, a Florida CPA firm, is the one Sam's List member mentioned near the end. Iota Finance is a paid featured member of Sam's List.

What the S Corp Built-In Gains Tax Is

The S corp built-in gains tax comes from IRC Section 1374. It generally applies to a corporation that was a C corporation and then became an S corporation, or received assets from one in certain carryover-basis transactions. If it sells an asset during a set window, the gain that built up while it was a C corporation can be taxed at the corporate level.

The limitation: the tax only applies when there is a gain to recognize inside the window. A conversion with no later sale, or a sale of assets with no built-in gain, generally produces no tax under this section.

The Section 1374 Recognition Period

The section 1374 recognition period is generally five years. It starts on the first day of the first tax year the corporation is an S corporation. Later gain is generally outside the tax.

Timing is where owners can act. A sale in year four can cost tax that the same sale in year six would not. Installment sales can blur this, because gain from a sale made inside the period can arrive later.

The limitation: waiting only helps if the business can afford to wait.

Which Gains Count

Only appreciation that existed on conversion day is in scope. If a building was worth $400,000 more than its tax basis when you converted, that $400,000 is the built-in gain.

The corporate tax is generally computed at the highest rate under IRC Section 11(b). That rate is currently 21 percent. A cap generally limits the total to the company's net unrealized built-in gain on conversion day, and taxable income limits also apply.

Say assets worth $1,000,000 had a tax basis of $600,000 at conversion, so the built-in gain is $400,000. If the company sells them for $1,000,000 in year three, the corporation could owe about 21 percent of $400,000, or $84,000, before other limits. The owners generally also report the gain personally, with the corporate tax flowing through as a loss that reduces it.

The limitation: this is a clean example, not a forecast. Real figures depend on valuation, liabilities, and other gains and losses.

Who Owes the S Corp Built-In Gains Tax

A company that has been an S corporation since it began generally is not exposed. The tax follows a C corporation history: a former C corporation is the obvious case, and a company that received assets from one can also be reached. It is not an extra personal rate on distributions, but a separate corporate tax on certain asset gains.

A sale of the S corporation's stock is generally a sale by the shareholders, not a corporate asset sale, so this tax is usually not the issue. An election that treats a stock deal as an asset sale, such as Section 338(h)(10), can change that.

The limitation: a buyer may insist on the structure that creates the tax. Check this before you sign a letter of intent.

Converting a C Corp to an S Corp: What to Settle First

Converting a C corp to an S corp is usually done with an election on Form 2553. Owners tend to focus on payroll tax savings and miss that conversion starts the built-in gains clock. Plan before a sale, not after, because most levers disappear once you sign.

Questions to settle with a CPA before converting or selling:

• What was each major asset worth on conversion day, and who will document it?
• Is a sale inside the five-year window likely, and could it wait?
• Would an asset sale or a stock sale leave more after tax?
• Do you hold LIFO inventory or installment sales, which carry their own timing rules?

The limitation: valuation on conversion day is the weak point, and a value set years later without records invites disputes.

Where a CPA Is Needed

A CPA handles the conversion-day valuation, the asset versus stock sale decision, LIFO and installment interactions, and the yearly calculation of recognized gain.

Iota Finance is a Florida-based accounting firm founded in 2022, with 7 employees and a nationwide client base. Its profile lists monthly accounting, tax and fractional CFO work for small businesses and startups, with minimums of $200,000 income or $500,000 revenue. You can see it on its Sam's List profile. Its profile does not say it handles built-in gains analysis, so ask.

Iota Finance has 14 verified client reviews on Sam's List as of 2026-10-02. Each review is submitted by an individual who identifies as a client of the firm and rates it on communication, subject-matter knowledge, and overall satisfaction. Reviews reflect those individual experiences and do not represent an endorsement by Sam's List. Iota Finance is a paid featured member of Sam's List. Ratings and rankings are not indicative of future performance or results.

The limitation: the stated minimums put smaller companies outside its range. A firm listed here is a starting point, not a verdict, so interview more than one. You can also browse accountants on Sam's List to compare options.

Frequently Asked Questions

How long does the built-in gains tax last?

Generally five years from the first day of the first tax year the company is an S corporation, and gain recognized after that is generally outside the tax. Congress has changed the length before, so ask a CPA to confirm it and your start date.

Does an S corp that was never a C corp pay it?

Generally no, because the tax is tied to a C corporation history. A company that received assets from a C corporation in certain transactions may still be reached, so check how the assets came to you.

Can I avoid the tax by selling stock instead of assets?

Often a stock sale is a sale by the shareholders, so this tax usually is not the issue. But a Section 338(h)(10) election can treat a stock deal as an asset sale. Ask a CPA to model both structures before you agree to terms.

If a sale or a conversion is on your horizon, list your major assets with their conversion-day values this week and take that list to a CPA.

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About the author: Kimberly Green is cofounder of Sam’s List, a directory and matching platform for financial professionals.