Q: When is a partnership return due?

On the 15th day of the third month after the partnership's year-end — 15 March for a calendar-year partnership, a month before the personal deadline. An automatic six-month extension to 15 September is available if you file for it. Americans abroad often miss this because it is earlier than the automatic 15 June personal deadline.

Do I have to file a US partnership return if my business is in the UK?

If you are a US person and the business is a partnership, US reporting usually follows. A US partnership files Form 1065; a foreign partnership (including many UK partnerships and LLPs) is reported by its US partners on Form 8865 if they control it or hold a 10%+ interest. Your share of profit flows to your personal US return via a Schedule K-1, taxable in the US wherever the business trades.

What is the penalty for filing Form 1065 late?

For 2025 tax-year returns the penalty is $255 per partner for each month (or part-month) the return is late, up to 12 months — even if no tax is due. A two-partner venture six months late owes $3,060. Form 8865 for foreign partnerships carries the same structure plus extra penalties for unreported interests, so the deadlines really matter.

Do I pay US self-employment tax on partnership income?

A general partner's share of active business income is generally subject to US self-employment tax (15.3%), which the Foreign Tax Credit cannot offset. However, the US/UK Totalization Agreement usually exempts you if you pay UK National Insurance, evidenced by a certificate of coverage. This is a key planning point for Americans partnering in a UK business.

How is a UK LLP treated for US tax?

The US generally treats a UK Limited Liability Partnership as a partnership, so a US member reports it on Form 8865 — but the classification can sometimes differ and can be elected. Because the US and UK treatments do not map neatly, anyone joining or running a UK LLP as a US person should confirm the US classification up front rather than assume.

Plenty of Americans abroad go into business with a local partner — a consultancy with a British colleague, a property venture, a creative studio. It feels informal, and in the UK it often is. But the US sees a partnership as a filing entity in its own right, and the moment a US person is a partner, US reporting can follow — on Form 1065 if the partnership is American, or Form 8865 if it is foreign. Get it wrong and the penalties are eye-watering: $255 per partner, per month, just for filing late. This guide explains when a US expat with a UK business partner has to file, what the forms involve, and how to stay out of trouble.

Why a partnership triggers US filing

A partnership is a 'pass-through' for US tax — it does not usually pay tax itself, but it must file an information return reporting its income, deductions and each partner's share, and it issues each partner a Schedule K-1 showing what to report on their own return. For a US person, that K-1 income is taxable in the US wherever the business operates. So even a small two-person venture with a UK partner can create a US filing obligation if a US person is involved, and the income flows through to the American's personal US return.

Form 1065 vs Form 8865 — which applies?

The form depends on where the partnership is formed. A US partnership (for example a US LLC taxed as a partnership) files Form 1065. A foreign partnership — including many ordinary UK business structures where two people simply trade together, and UK LLPs — is reported by its US partners on Form 8865, which mirrors much of Form 1065 but sits on the US person's own return.

US partnership (e.g. US multi-member LLC): files Form 1065; partners get K-1s.
Foreign partnership (incl. many UK general partnerships and LLPs): US partners may file Form 8865 if they control it or hold a 10%+ interest.
A UK LLP is often treated as a partnership for US purposes — but the classification can be elected, so check before assuming.

The $255-per-partner penalty

Form 1065 carries one of the harshest 'no tax due' penalties in the code. For 2025 tax-year returns the late-filing penalty is $255 per partner for each month (or part-month) the return is late, up to 12 months — and it applies even though the partnership itself owes no tax. A two-partner venture that files six months late faces $255 × 2 × 6 = $3,060; a larger partnership can run into five figures fast. The same penalty structure applies to Form 8865 for foreign partnerships, and Form 8865 can stack additional penalties for failures to report. This is exactly why partnership deadlines are not to be missed.

The deadline is earlier than you think

Partnership returns are due on the 15th day of the third month after year-end — 15 March for a calendar-year partnership, a full month before the personal 15 April deadline. An automatic six-month extension to 15 September is available, but you must file the extension. Americans abroad, used to the automatic 15 June personal deadline, are often caught out by the earlier partnership date. Because the K-1 feeds your personal return, a late partnership filing also delays your own taxes.

How partnership income is taxed for the US partner

Your share of the partnership's profit flows onto your US return via the K-1 and is taxed as US income, even if the business is entirely UK-based and the money never leaves Britain. The good news is that UK tax you pay on the same profit can usually be claimed as a Foreign Tax Credit, preventing double taxation. Self-employment tax can also arise on a US partner's share of trade or business income — though the US/UK Totalization Agreement may exempt you if you pay UK National Insurance, evidenced by a certificate of coverage. The interaction is fiddly and worth modelling.

Self-employment tax on partnership income

A general partner's distributive share of the partnership's active business income is generally subject to US self-employment tax (15.3%), not just income tax — a cost the Foreign Tax Credit cannot offset because self-employment tax is not an income tax. For an American partnering in a UK business, the Totalization Agreement is usually what removes this charge, by assigning you to the UK National Insurance system. Keep your certificate of coverage with your records, and use our US self-employment tax calculator to see what the charge would otherwise be.

It often comes with Form 5471 and FBAR

A partnership rarely files alone. If the venture is run through a UK limited company rather than a partnership, you may instead be in Form 5471 territory with its own controlled-foreign-corporation rules. Either way, the business's UK bank accounts — if you have signature authority — can push you over the FBAR threshold, and larger interests can trigger Form 8938. Mapping all the related filings together is essential; the partnership return is usually the centrepiece of a small cluster of disclosures.

UK LLPs: a common trap

UK Limited Liability Partnerships are popular for professional firms, but for a US partner they are a classic cross-border trap. The US generally treats a UK LLP as a partnership (so Form 8865 reporting applies), but an LLP can sometimes be classified differently, and the members' UK tax treatment does not map neatly onto the US rules. If you are a US person joining or running a UK LLP, get the US classification confirmed up front — retrofitting the right treatment after years of filings is painful and expensive.

What you actually need to file

The partnership return itself — Form 1065 (US partnership) or Form 8865 (foreign partnership) for the US partner.
A Schedule K-1 for each partner, showing their share of income and deductions.
Your personal Form 1040 reporting the K-1 income, with Foreign Tax Credit claims for UK tax paid.
FBAR / Form 8938 if the business accounts bring you over the thresholds.
A certificate of coverage if you are relying on the Totalization Agreement to avoid US self-employment tax.

If you are already behind

Many Americans discover the partnership-filing requirement late, having reported their personal income but never the partnership return or Form 8865. Because the penalties are steep, the fix matters. Where the gap is part of a wider compliance problem, the IRS Streamlined Filing Procedures can sometimes bring everything current and mitigate penalties for non-wilful taxpayers. Where your returns are otherwise clean, reasonable-cause relief or first-time abatement may apply to the partnership penalty. Acting before the IRS contacts you is far better than waiting.

Plan the structure before you partner up

The cheapest way to handle partnership tax is to get the structure right at the start. Before you go into business with a UK partner, decide deliberately whether a partnership, an LLP or a company is best given your US position, and line up the US filings from day one. A US/UK tax specialist can map the entity choice, the K-1 mechanics and the Totalization position before you sign anything — turning a potential compliance headache into a routine annual filing.