The Section 1375 Sting Tax: How Former C Corps Pay 21% on Passive Income and Lose Their S Election After Three Years

Most S corporation owners assume the conversion from C corp status is a one-way door — flip the switch, file Form 2553, and never think about subchapter C again. Then a portfolio of bonds, a piece of rental real estate, or a chunky royalty check pushes passive income above a quiet 25% threshold, and the IRS slaps a flat 21% corporate-rate tax on what should have been pass-through earnings. Three years of that pattern and the S election itself vanishes by operation of law.

This is the world of Section 1375 — the "sting tax" on excess net passive income — and Section 1362(d)(3), its companion termination cliff. The two provisions together police a narrow but ruthless rule: an S corp that still carries accumulated earnings and profits (E&P) from prior C years cannot let passive income dominate its receipts. Founders who took over a family business, buyers who acquired a former C corporation via stock sale, and any S corp that absorbed C-corp E&P through reorganization all live under these rules whether they realize it or not.

Here is what the sting tax is, when it bites, and the planning moves that defuse it before April 15.

What Triggers the Sting Tax

Section 1375 applies only when an S corporation meets both of two conditions at year-end:

1. The corporation has accumulated subchapter C earnings and profits (E&P) at the close of the year, and
2. Passive investment income exceeds 25% of gross receipts for the year.

If either condition fails, no tax. An S corp that has always been an S corp from the day of incorporation — and never absorbed C-corp E&P through a tax-free reorganization — has zero C E&P and is immune to Section 1375 forever. That is the single most important sentence in this entire article: the sting tax is exclusively a former-C-corp problem.

But many S corporations carry C E&P without their owners knowing. Common paths to inheriting it include:

• A C corporation that elected S status under subchapter S after years of operating as a C, leaving retained earnings on the books that became C E&P on the conversion date.
• An S corporation that merged with or acquired a C corporation in a tax-free reorganization under Section 368, inheriting the target's E&P balance.
• A QSub election that brought a C subsidiary into the consolidated S group, layering its E&P onto the parent.

Once C E&P exists, it does not expire on its own. It sits on the balance sheet until the S corp affirmatively distributes it under the Section 1368 ordering rules, makes a "deemed dividend" election, or is liquidated.

Defining "Passive Investment Income" and "Gross Receipts"

The statute borrows its definition of passive investment income from Section 1362(d)(3)(C). It includes gross receipts from:

• Royalties — including trademark licensing payments
• Rents — unless the S corp is in the active trade or business of renting property, which generally requires significant services or substantial costs
• Dividends — including Section 316 dividends from underlying portfolio holdings
• Interest — except interest from sales of inventory in the ordinary course, and interest earned by lending or finance companies in their core business
• Annuities
• Gains from sales or exchanges of stock or securities — note this is gross sale proceeds netted against basis on a transaction-by-transaction basis, not the gross sale amount

What is not passive investment income for this purpose: ordinary operating revenue from selling goods or services, fees for active management, capital gains on operating assets, and rents tied to genuine real estate operating businesses with significant services.

"Gross receipts" is the broader denominator. It captures essentially all income from operations, including return of capital on sales of inventory and active-business revenue. The trick is that the numerator (passive income) is narrowly defined while the denominator (gross receipts) is broad, which generally favors the taxpayer — but only if the corporation runs a meaningful operating business alongside its passive holdings.

The Excess Net Passive Income Formula

When both conditions are met, the tax base is excess net passive income (ENPI) — not gross passive income. The math has three steps.

Step 1: Compute net passive income. Take passive investment income and reduce it by deductions directly connected with producing that income (investment management fees, property taxes on rental units, depreciation on rented assets, etc.).

Step 2: Compute the excess fraction. Divide the amount by which passive investment income exceeds 25% of gross receipts by total passive investment income. In formula form:

Excess Fraction = (Passive Investment Income − 25% × Gross Receipts) ÷ Passive Investment Income

Step 3: Multiply. Excess net passive income equals net passive income × the excess fraction.

A worked example makes this concrete. Suppose an S corp former C corp has:

• Gross receipts: $1,000,000
• Passive investment income: $400,000 (interest and rent)
• Deductions directly connected to passive income: $50,000

Net passive income = $400,000 − $50,000 = $350,000.

Excess fraction = ($400,000 − $250,000) ÷ $400,000 = 37.5%.

ENPI = $350,000 × 0.375 = $131,250.

Sting tax = $131,250 × 21% = $27,562.50.

That tax is owed at the corporate level by the S corp itself, then the remaining passive income still flows through to shareholders on Schedule K-1 — but reduced by the sting tax paid, so shareholders absorb a smaller pass-through amount. There is also a critical limitation: ENPI can never exceed the corporation's taxable income (computed as if it were a C corp, with certain modifications), so a loss-year S corp does not owe the tax even if passive income mechanically exceeds 25% of gross receipts.

The Three-Year Termination Cliff Under Section 1362(d)(3)

Section 1375 is the annual financial hit. Section 1362(d)(3) is the existential one.

If an S corporation has C E&P at the end of three consecutive taxable years and passive investment income exceeds 25% of gross receipts in each of those three years, the S election automatically terminates as of the first day of the fourth year. The corporation reverts to C status without any election or notice from the IRS.

Termination is automatic and triggers cascading consequences:

• The newly minted C corp is taxed at the corporate rate on all its income going forward.
• A five-year waiting period under Section 1362(g) applies before a new S election can be made (unless the IRS consents to an earlier re-election).
• Existing shareholders may discover too late that their tax planning, basis tracking, and distribution strategy all assumed pass-through treatment.

This is why monitoring passive income year over year matters more than the sting tax bill itself. A single bad year is expensive. Three bad years are catastrophic.

How Accurate Bookkeeping Prevents the Sting

The arithmetic of Section 1375 is mechanical, but it relies on disciplined record-keeping in three places that ordinary small-business bookkeeping often blurs together:

1. A running C E&P balance — Many S corp owners never compute this number after the conversion. Without a tracked balance, they cannot tell whether they have already bled it out or whether risk remains.
2. Segregation of passive vs. active receipts — Rents, royalties, interest, and dividends need their own ledger accounts so the 25% test can be run mid-year, not as a year-end surprise.
3. The Accumulated Adjustments Account (AAA) — Under Section 1368, distributions from an S corp with C E&P come first out of AAA (tax-free, basis-reducing), then out of C E&P (taxable dividends), then out of remaining stock basis. Without an accurate AAA, the corporation cannot execute a clean E&P bleed-out.

Maintaining transparent, version-controlled books for these accounts is the difference between a planned distribution strategy and a surprise audit finding.

The Three Real-World Planning Moves

Owners who detect Section 1375 exposure have three time-tested responses.

1. Bleed Out the E&P With Targeted Distributions

The cleanest fix is to eliminate the C E&P balance entirely. Once C E&P is zero, Section 1375 cannot apply no matter how much passive income the corporation earns.

Two mechanisms exist:

• Regular Section 1368 distributions that exceed the AAA balance. Once AAA is exhausted, the next dollars distributed come out of C E&P and are taxable dividends to shareholders. This is the standard path, but it requires shareholders to absorb dividend tax to clear the balance.
• A "deemed dividend" election under Reg. §1.1368-1(f)(3). The corporation elects to treat itself as having distributed a hypothetical dividend equal to all C E&P, immediately followed by a contribution back to capital. No cash moves, but the E&P is purged. Shareholders still owe tax on the deemed dividend, but the corporation is forever free of Section 1375.

The deemed dividend election is particularly useful when the corporation lacks cash to make actual distributions but the shareholders can absorb the dividend tax.

2. Manage the Passive Income Ratio

If E&P elimination is not feasible, the lever is the 25% test itself. Two ways to keep passive income below the line:

• Grow gross receipts. Adding active business revenue dilutes the passive fraction. A real estate S corp can layer in property management services to convert pure rental income into active business income.
• Defer passive income into a year when gross receipts will be higher, or accelerate active income to the same year.

The 25% test is annual, so this is a tactical lever pulled at year-end, not a structural fix.

3. Request a Section 1375(d) Waiver

Section 1375(d) gives the IRS authority to waive the sting tax if:

• The corporation determined in good faith that it had no C E&P at year-end, and
• Within a reasonable period after discovering the E&P existed, the corporation distributed it.

This is a narrow safety valve, typically used when a post-acquisition E&P study reveals a balance the new owners did not know about. The waiver is discretionary and requires a formal ruling request — but it exists for a reason and is granted in genuine good-faith cases.

A Sample Year-End Sting Tax Worksheet

A simple worksheet keeps the analysis tight:

Run this in October, not April. If line 4 is positive and C E&P is on the balance sheet, there is still time to declare a distribution, accelerate active revenue, or trigger the deemed dividend election before year-end.

Where People Get This Wrong

Three recurring mistakes:

Treating Section 1375 as an obscure rule that won't apply. Any S corp with prior C E&P should run the 25% test annually. Acquired businesses, family-succession conversions, and tax-free reorganizations all create silent E&P exposure.

Confusing "passive activity" rules with "passive investment income." Section 469 passive activity rules apply to individual shareholders and limit loss deductions. Section 1375 is a corporate-level test with its own narrow definition. The two regimes share nothing but the word "passive."

Forgetting the three-year clock. Even if the sting tax is small, three consecutive years above the 25% threshold ends the S election. Track the clock from the first year of excess, not from the first year of large tax due.

Keep Your Pass-Through Status Safe From Day One

The Section 1375 sting tax punishes hybrid structures — operating S corps that drift into passive holding companies without first cleaning up the C-corp history they carry. Avoiding it requires three small disciplines done consistently: track C E&P after every transaction that could create it, segregate passive from active receipts in your chart of accounts, and run the 25% test in real time rather than at year-end.

Beancount.io gives S corporation owners a plain-text accounting ledger that is transparent, version-controlled, and easy to audit — every E&P movement, distribution, and passive-versus-active classification leaves a tracked trail you can review years later. No black boxes, no vendor lock-in, and no surprise April reconciliations. Get started for free and see why founders and finance professionals are switching to plain-text accounting for the kind of multi-year balances that matter.