A founder we spoke with last quarter set up a software company in Ireland, kept all the profits offshore to fund product development, and assumed she wouldn't owe U.S. tax until she paid herself a dividend years later. When her CPA finished her return, she discovered she owed personal income tax on more than $400,000 of "income" she had never received. The cash was sitting in a Dublin bank account. The tax bill was due April 15 in Texas.
That is Subpart F in one paragraph. It is the rulebook that decides when the IRS forces a U.S. shareholder of a foreign corporation to recognize income immediately, on a current-year basis, even if no money has crossed a border. The rules were written in 1962 to stop large companies from parking passive income in low-tax jurisdictions. Sixty years later they sweep up small business owners, expat entrepreneurs, and inheritors of foreign family companies who often have no idea they fall inside the net.
This guide walks through who counts as a U.S. shareholder, what makes a foreign company a Controlled Foreign Corporation (CFC), what types of income trigger an inclusion, how the constructive ownership rules pull in family members and related entities, and how the 2026 changes from the One Big Beautiful Bill Act (OBBBA) reshaped the landscape.
The Two-Step Test: Are You a U.S. Shareholder of a CFC?
Two definitions do most of the work in this area, and both must be satisfied before Subpart F applies.
Step One: Are You a "U.S. Shareholder"?
Under Internal Revenue Code Section 951(b), a U.S. shareholder is any U.S. person who owns at least 10 percent of a foreign corporation by vote or value. "U.S. person" includes citizens, green card holders, U.S. tax residents, domestic corporations, partnerships, trusts, and estates. The 10 percent test is measured directly, indirectly through entities, and constructively under the attribution rules of Section 958, which we cover further below.
The test is binary. If you cross 10 percent on any single day of the corporation's tax year, you are a U.S. shareholder for that year. If you sit at 9.9 percent, you escape Subpart F entirely, but you may still face other reporting obligations.
Step Two: Is the Foreign Corporation a CFC?
A foreign corporation becomes a Controlled Foreign Corporation when U.S. shareholders, in the aggregate, own more than 50 percent of vote or value on any day during the tax year. The 50 percent threshold uses the same direct, indirect, and constructive rules from Section 958. If five unrelated U.S. shareholders each own 11 percent of an Irish company and the remaining 45 percent sits with foreign investors, the company is a CFC because the U.S. owners aggregate to 55 percent.
CFC status is sticky. Once a foreign corporation is a CFC, every U.S. shareholder must include their pro rata share of Subpart F income on their U.S. return for that year, whether or not a dividend is paid.
What Income Actually Triggers a Subpart F Inclusion
Not every dollar earned by a CFC flows through to U.S. shareholders. The statute targets specific categories of income that Congress viewed as easily shifted to low-tax jurisdictions. The four most common categories:
Foreign Personal Holding Company Income (FPHCI)
This is the big one. Section 954(c) captures passive income: interest, dividends, royalties, rents, annuities, and net gains from property that produces such income. If your CFC parks excess cash in a money market fund, the interest is Subpart F income. If it holds intellectual property and licenses it to affiliates, the royalties are Subpart F income.
The permanent CFC look-through rule under Section 954(c)(6), made permanent by recent legislation, can exclude related-party FPHCI when the underlying income at the payor CFC is active. This is a planning lifeline for groups with operating subsidiaries that pay interest or royalties up through holding companies.
Foreign Base Company Sales Income (FBCSI)
When a CFC buys goods from a related party and sells them to another related party for use outside the CFC's country of incorporation, the profit is generally Subpart F income. The classic structure this targets: a U.S. parent sells finished goods to an Irish subsidiary at a low price, which then resells to European customers, leaving the profit in Ireland. The exception is real operational substance. If the CFC actually manufactures the product, or the goods are sold for use in the CFC's home country, the income is excluded.
Foreign Base Company Services Income (FBCSvI)
Services performed by a CFC for or on behalf of a related party, where the services are performed outside the CFC's country of incorporation, generate Subpart F income. Software consulting work done by an Indian CFC for a U.S. parent's customers in Germany is the prototypical fact pattern.
Insurance Income
Section 953 sweeps in premium income from insuring U.S. risks or risks of related parties. The captive insurance industry lives and dies by these rules.
Income That Escapes Subpart F
Three exceptions matter for most small-business CFCs:
- De minimis rule: If gross Subpart F income is less than the lesser of $1 million or 5 percent of the CFC's gross income, none of it counts.
- Full inclusion rule (the trap): If Subpart F categories exceed 70 percent of gross income, the entire gross income becomes Subpart F income. The 70 percent cliff is brutal for holding companies.
- High-tax exception: Income subject to an effective foreign tax rate above 90 percent of the maximum U.S. corporate rate is excluded. With the U.S. corporate rate at 21 percent, the threshold is 18.9 percent. An Irish CFC paying Ireland's 12.5 percent corporate tax fails the test; a German CFC at roughly 30 percent passes.
Constructive Ownership: How Family Members and Trusts Pull You In
The attribution rules under Section 958(b) are the most-missed piece of CFC planning. They borrow heavily from Section 318 and treat you as owning stock that is technically owned by people and entities connected to you. Some of the more counterintuitive results:
- Family attribution: You constructively own stock held by your spouse, children, grandchildren, and parents. Siblings do not count.
- Entity attribution: Stock owned by a partnership, estate, trust, or corporation is attributed to its owners or beneficiaries. If a 50 percent partner in a U.S. LLC personally owns 6 percent of a foreign corporation, and the LLC owns another 5 percent, the partner is a 10 percent U.S. shareholder.
- Nonresident alien exception: There is no attribution from a nonresident alien relative for purposes of determining U.S. shareholder status. A U.S. citizen married to a foreign national does not pick up the spouse's shares in a foreign company solely because of marriage.
- Downward attribution (the OBBBA reset): From 2018 through 2025, the Tax Cuts and Jobs Act repealed the prohibition on attributing stock from a foreign person down to a U.S. entity. That repeal swept thousands of innocent U.S. subsidiaries of foreign multinationals into the CFC net. The OBBBA restored the prohibition for tax years of foreign corporations beginning after December 31, 2025. Many U.S. companies that filed Form 5471 every year for a Korean or German parent's brother-sister affiliate no longer need to do so.
If a single chain of attribution makes the math work, you cross the threshold. Map your family tree and entity stack before assuming you are safe.
Form 5471: The Filing Mechanic
The disclosure vehicle is Form 5471, "Information Return of U.S. Persons With Respect to Certain Foreign Corporations." Filers fall into one of five categories, with several subcategories added in recent years to capture different attribution patterns:
- Category 1: U.S. shareholders of a Section 965 specified foreign corporation.
- Category 2: U.S. officers and directors of a foreign corporation when a U.S. person acquires at least 10 percent ownership.
- Category 3: U.S. persons who acquire or dispose of stock crossing the 10 percent threshold, or who become U.S. persons while holding 10 percent.
- Category 4: U.S. persons who controlled (more than 50 percent) the foreign corporation for at least 30 consecutive days during the year.
- Category 5: U.S. shareholders of a CFC on the last day of the year the corporation is a CFC. Subdivided into 5a (unrelated section 958(a) shareholders), 5b (unrelated constructive shareholders), and 5c (related constructive shareholders).
The schedules required depend on the category. A Category 5a filer reports Subpart F inclusions on Schedule I, NCTI on Schedule I-1, earnings and profits on Schedules H and J, and intercompany transactions on Schedule M. The form runs more than 20 pages and is one of the most complex returns in the U.S. tax code.
The penalty for failing to file is at least $10,000 per CFC per year, with an additional $10,000 per month after IRS notice (capped at $50,000 per form). Penalties apply even when no tax is owed. The statute of limitations on the entire return stays open until the form is filed, which is the hidden danger: a missed Form 5471 keeps every line of your Form 1040 audit-eligible indefinitely.
What Happens After Inclusion: PTEP and Basis Adjustments
Once Subpart F income is taxed at the U.S. shareholder level, the same dollars should not be taxed again when the CFC distributes them. Section 959 carves these dollars out as Previously Taxed Earnings and Profits (PTEP). A distribution sourced from PTEP is excluded from gross income.
Section 961 makes the corresponding basis adjustments. When you include Subpart F income, your basis in the CFC stock increases. When you later receive a PTEP distribution, your basis decreases by the same amount. Without these adjustments you would pay tax twice: once on the inclusion and again when you sell the stock at an artificially low basis.
Treasury proposed sweeping new PTEP and basis regulations in late 2024 to consolidate decades of accumulated guidance. The mechanics are intricate, particularly for tiered CFC structures and shareholders who own through partnerships. Track PTEP year by year, by category, by currency, and by source. A CFC that has been running for a decade can easily accumulate a dozen distinct PTEP "buckets," each with its own ordering and taxation rules.
What Changed in 2026: The OBBBA Rewrite
The One Big Beautiful Bill Act, signed July 4, 2025, reset large parts of the international tax regime effective for tax years beginning after December 31, 2025. The headline changes:
- GILTI is renamed NCTI (Net CFC Tested Income) under a revised Section 951A. The qualified business asset investment (QBAI) deemed return is eliminated, so the entire tested income flows up rather than only the amount above a 10 percent return on tangible assets.
- The Section 250 deduction that applied to GILTI drops from 50 percent to a permanent 40 percent. With a 21 percent corporate rate, the effective NCTI rate for C corporations becomes 12.6 percent, up from the prior 10.5 percent.
- The foreign tax credit allowed against NCTI rises from 80 percent to 90 percent, partially offsetting the rate increase for high-tax foreign operations.
- Section 958(b)(4) is restored, ending the post-TCJA downward attribution regime that swept brother-sister U.S. affiliates of foreign parents into the CFC net.
- A new Section 951B captures foreign-controlled structures that used to escape under the old attribution rules.
For individual shareholders the bottom line is that more income flows up than before (no QBAI shelter), and the rate, after the reduced 250 deduction and improved FTC, is still roughly 12 to 14 percent for high-tax foreign operations.
Practical Planning Moves
Even sophisticated CFC owners can lose six figures to avoidable mistakes. The patterns we see most often:
- Test the de minimis exception every year. A CFC that just clears the $1 million floor in passive income can save tens of thousands by trimming a money-market position before year-end. Track the running total quarterly so December does not produce a surprise.
- Document the high-tax exception election. The election is annual and must be made by the controlling domestic shareholder. Without paperwork, foreign operations subject to 25 percent local tax can still trigger U.S. inclusions because the election was never properly filed.
- Track PTEP religiously. Every Subpart F or NCTI inclusion adds to PTEP and to basis. Every distribution reduces PTEP and basis in a specific order. Lose the records and you risk paying tax twice on the same dollar of foreign earnings, either at distribution or at exit.
- Map family attribution before the audit. If a foreign grandparent gifts shares to a U.S. grandchild during the year, the entire CFC analysis can flip mid-year. Run the constructive ownership math whenever a family ownership event occurs.
- Reconsider entity choice. A check-the-box election to treat a CFC as a disregarded entity or partnership can eliminate Subpart F entirely (no foreign corporation exists for U.S. purposes), but the election has its own immigration and exit considerations and is irreversible for five years.
- Watch the calendar around acquisitions. Becoming a 10 percent shareholder for even a single day creates Category 3 filing requirements. Selling out before December 31 of a CFC year does not eliminate the inclusion if you were a shareholder mid-year.
Records That Save You at Audit Time
The recurring theme in every IRS notice we see on this topic is documentation. Subpart F audits are rarely about the law; they are about whether the taxpayer can prove what the numbers actually were. A workable records system includes:
- A standing chart of CFC ownership, refreshed annually, that documents direct, indirect, and constructive percentages for each U.S. shareholder.
- Year-by-year Subpart F income calculations broken down by category, with copies of the underlying CFC trial balance translated to U.S. GAAP and U.S. dollars.
- A running PTEP ledger by inclusion year, category, and foreign tax pool.
- Source documents for every related-party transaction (loans, royalty agreements, services contracts), since these drive the FPHCI and FBCSI analysis.
- Foreign tax filings for each CFC, supporting the high-tax exception and the foreign tax credit.
For most small business owners, that level of detail outstrips what their general-ledger software can produce. Plain-text accounting platforms make this easier because every entry, every account, and every adjustment lives in human-readable files that auditors can trace without depending on a vendor's proprietary database.
Keep Your International Records Audit-Ready
Subpart F audits are won and lost on records. If you own even a slice of a foreign corporation, you need ledgers that show, in plain numbers, where every dollar of foreign income came from, when you included it, and how much PTEP and basis you have left. Beancount.io is a plain-text accounting platform purpose-built for this kind of transparent, version-controlled bookkeeping. Every transaction is human-readable, every report is reproducible, and nothing is locked inside a proprietary database that an examiner cannot read. Get started for free and keep your international filings defensible from day one.