If your agency earns money from clients outside the UK, you cannot leave that income off your corporation tax return. HMRC expects you to report it. The question is how, and where, and whether you end up paying tax twice.

I deal with this question regularly from agency founders who have picked up a US client, a European retainer, or a project from a Middle Eastern brand. The instinct is to assume that if the client is overseas, the income is somehow outside the UK tax net. It is not. Your agency is UK-resident. Your worldwide profits are chargeable to corporation tax.

This article walks through what counts as foreign income, how to report foreign income on your agency's corporation tax return, and how to make sure you are not paying more tax than you need to.

What Counts as Foreign Income for a UK Agency

Foreign income is any income that originates from outside the UK. For a UK-based agency, this typically falls into a few categories.

Overseas client fees. A marketing agency in Shoreditch billing a SaaS company in San Francisco. A PR agency in Manchester working with a German automotive brand. A web design agency in Bristol building a site for a Dubai property developer. The location of the client does not matter for UK tax purposes. What matters is where the agency is resident.

Foreign branch or permanent establishment profits. If you have opened an office in Dubai, a subsidiary in the US, or a permanent establishment in any other country, the profits attributable to that branch are still subject to UK corporation tax. You may also owe tax in the local jurisdiction, which is where double tax treaties come in.

Interest on overseas bank accounts. If your agency holds funds in a foreign currency account or an overseas bank account, the interest earned is foreign income. Same treatment as UK bank interest for corporation tax purposes, but you may have had withholding tax deducted at source.

Royalties or licensing income. If your agency licenses software, intellectual property, or creative assets to an overseas party, the royalty income is foreign-sourced. Again, reportable in the UK.

Dividends from overseas subsidiaries. If your agency owns shares in a foreign company and receives dividends, those dividends are foreign income. The tax treatment depends on whether the subsidiary is in a treaty country and whether the dividend is exempt under the UK's participation exemption.

If any of these apply to your agency, you need to know how to report them correctly.

Where Foreign Income Goes on the CT600

The CT600 is HMRC's main corporation tax return form. It has multiple supplementary pages. The standard CT600 has a single box for turnover and a single box for other income. Foreign income does not automatically get its own line on the main form.

Instead, you report foreign income in the same boxes as UK income on the main CT600. The distinction matters for the computational pages and the tax calculation, not for the basic return form itself.

Here is the practical approach.

Step one: include foreign income in your total turnover. Box 1 on the CT600 asks for turnover. Your total turnover includes all income from all sources, UK and overseas. Do not net off foreign income or try to exclude it because it came from abroad. HMRC expects the full figure.

Step two: use the supplementary pages. If your foreign income is significant, or if you are claiming double tax relief, you will need to complete the CT600J supplementary page. This is the page for claiming relief from double taxation. It asks for details of the foreign income, the foreign tax paid, and the relief you are claiming.

Step three: adjust the tax computation. Your corporation tax computation is where you break down the profit figure. Foreign income is included in the profit figure, but you then deduct any double tax relief to arrive at the net UK tax payable.

If your agency has a simple structure with occasional overseas invoices, the process is straightforward. If you have a foreign branch, overseas subsidiaries, or complex withholding tax arrangements, the computation gets more detailed.

Double Tax Relief: The Key Mechanism

The UK has double tax treaties with over 130 countries. These treaties exist to stop you paying tax twice on the same income. If your agency pays tax in a foreign country on income that is also chargeable to UK corporation tax, you can claim double tax relief.

There are two main methods.

Unilateral relief. If there is no double tax treaty with the country where the income arose, you can still claim relief unilaterally under UK law. The relief is the lower of the foreign tax paid and the UK corporation tax due on that income.

Treaty relief. If there is a double tax treaty, the treaty usually specifies which country has the primary taxing right. In many cases, the UK gives credit for foreign tax paid, up to the amount of UK corporation tax attributable to that income.

Here is a worked example.

Your agency earns £50,000 from a US client. The US imposes a 10% withholding tax on service fees, so £5,000 is deducted at source. You receive £45,000. Your UK corporation tax rate is 19% (assuming profits are under £50,000 and you qualify for the small profits rate). UK corporation tax on that £50,000 would be £9,500. You claim double tax relief of £5,000, reducing your UK tax bill to £4,500 on that income.

Without the relief, you would have paid £5,000 to the US and £9,500 to the UK. Total: £14,500 on £50,000 of income. With relief, you pay £5,000 to the US and £4,500 to the UK. Total: £9,500. That is the correct outcome.

The relief is claimed on the CT600J supplementary page. Your accountant will need details of the foreign tax paid, the date it was paid, and the treaty article under which relief is claimed.

Foreign Branch or Permanent Establishment

If your agency has a physical presence overseas, the tax treatment changes. A foreign branch is not a separate legal entity. It is part of your UK agency. But the profits attributable to that branch may also be taxable in the local jurisdiction.

Under UK law, you report the branch profits in your UK corporation tax return. You then claim double tax relief for any local tax paid. The key is to ensure the branch is not treated as a separate company for local tax purposes, or you may end up with a different set of compliance obligations.

For example, if your agency sets up a branch in Dubai, the Dubai branch may be subject to 9% corporation tax under the new UAE corporate tax regime (effective from June 2023). You report the branch profits in your UK CT600, then claim credit for the UAE tax paid. The net effect is that you pay the higher of the two tax rates, not both.

If you are considering a foreign branch structure, speak to your accountant before you open the branch. The tax compliance requirements can be significant, and the cost of getting it wrong is high.

Transfer Pricing and Foreign Transactions

If your agency transacts with a related party overseas, transfer pricing rules apply. A related party could be a subsidiary, a parent company, or a company under common control. The rule is simple: transactions must be at arm's length. You cannot charge an overseas subsidiary an inflated fee to shift profits out of the UK, or accept a low fee from a related party to avoid UK tax.

HMRC expects you to have transfer pricing documentation in place if your transactions with related parties exceed certain thresholds. For most small and medium-sized agencies, the threshold is £1 million in transactions per year. If you exceed that, you need a transfer pricing policy and supporting evidence.

This is relevant because foreign income often involves cross-border related party transactions. If your agency has a US subsidiary and you charge management fees, or if you license IP to a European affiliate, transfer pricing applies.

Foreign Currency and Exchange Rate Issues

Foreign income is usually received in a foreign currency. For UK corporation tax purposes, you must convert that income into sterling. HMRC accepts several methods, but the most common is to use the exchange rate on the date the income is recognised in your accounts.

If you use accounting software like Xero or QuickBooks, the software will typically handle the conversion automatically if you set the base currency to GBP and enter transactions in the foreign currency. The software uses the spot rate on the transaction date.

Exchange rate fluctuations can create taxable gains or losses. If you hold foreign currency in a bank account and the exchange rate moves, you may have a foreign exchange gain or loss when you convert it. That gain or loss is taxable or deductible for corporation tax purposes.

Keep a record of the exchange rates used. HMRC may ask for them if they open an enquiry into your return.

Common Mistakes When Reporting Foreign Income

I see the same errors repeatedly from agency founders who report foreign income for the first time.

Omitting foreign income entirely. The most common mistake. A founder assumes that because the client is overseas, the income is not taxable in the UK. It is. HMRC receives data from foreign tax authorities under automatic exchange of information agreements. They will find out.

Failing to claim double tax relief. Some founders pay foreign tax and then pay UK tax on the same income without claiming credit. This is expensive. The CT600J form is straightforward. Use it.

Using the wrong exchange rate. If you use an average rate for the year instead of the spot rate on the transaction date, you may misstate the income. HMRC will accept a reasonable method consistently applied, but you need to document it.

Not reporting foreign bank accounts. If your agency has a bank account in Dubai, the US, or anywhere else, the interest and any foreign tax deducted must be reported. HMRC's automatic exchange agreements cover bank account data. They will know.

Ignoring withholding tax. Many countries deduct withholding tax on service fees, royalties, or dividends. If you do not claim credit for that withholding tax, you lose it. You cannot reclaim it later in most cases.

When to Speak to Your Accountant

If your agency has foreign income, you should not file your corporation tax return without your accountant reviewing the foreign income entries. The CT600J form is not complicated, but the underlying calculations can be.

Specific triggers to ask your accountant about:

  • Your agency has invoiced an overseas client for the first time.
  • You have opened a foreign bank account or a foreign subsidiary.
  • You have received a dividend from an overseas company.
  • You have paid foreign tax on any income.
  • Your agency has a permanent establishment or branch overseas.
  • You are considering moving overseas or restructuring your agency with an international element.

Our ICAEW qualified team at Agency Founder Finance works with agency founders who have international income streams. We handle the CT600, the CT600J, the double tax relief computations, and the transfer pricing documentation. If your agency has foreign income, get it on the return correctly from day one.

Summary

Foreign income is taxable in the UK. Report it on your CT600 in the same boxes as UK income, then use the CT600J supplementary page to claim double tax relief. Keep records of exchange rates, foreign tax paid, and the treaty articles you rely on. Do not assume that because the client is overseas, HMRC does not need to know.

If you are unsure whether your agency's foreign income is being reported correctly, ask your accountant before you file. A correction after filing is more expensive than getting it right the first time.