Patent Box: How the 10% Corporation Tax Rate Actually Works (2026)
The Patent Box regime taxes profit from qualifying patented inventions at an effective 10% rate instead of the standard 25% corporation tax rate. Here's what qualifies and how the calculation works.
What Patent Box is designed to encourage
Patent Box was introduced to encourage companies to both develop patentable innovations and commercialise them from within the UK, by offering a substantially reduced effective corporation tax rate — 10% — on the profit specifically attributable to qualifying patented inventions, rather than the standard 25% main rate (or 19% small profits rate) that would otherwise apply to all company profit.
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| Patent source | Qualifies for Patent Box? |
|---|---|
| UK Intellectual Property Office (UK IPO) | Yes |
| European Patent Office (EPO) | Yes |
| Certain other approved European national patent offices | Yes |
| US Patent and Trademark Office (USPTO) only, no UK/EPO equivalent | No |
| Trademarks, copyright, design rights (standalone) | No |
| Supplementary protection certificates, certain plant variety rights | Yes (specific additional qualifying rights) |
This list matters because a company holding only US patents, without an equivalent UK or European patent, would not qualify for Patent Box relief on that IP, even if the underlying invention is commercially significant.
The "nexus" requirement: you must have done the development
A critical condition — often the one that catches companies out — is the nexus requirement: you (or your corporate group) must have genuinely undertaken qualifying development activity on the patented invention. Simply acquiring a patent from an unconnected third party, without doing meaningful development work on it yourself, significantly restricts (or can eliminate) the relief available.
How the calculation works, simplified
The full Patent Box calculation is genuinely complex, but broadly follows these steps:
- Identify total qualifying IP income — this includes income from selling patented products, licensing royalties for the patent, and any infringement or disposal income related to the qualifying IP.
- Calculate the relevant IP profit — broadly, an apportionment of the company's total profit attributable to that qualifying IP income, after deducting a routine return (a notional profit margin assumed to arise from routine business functions unrelated to the patent itself) and, in some cases, a marketing asset return.
- Apply the nexus fraction — this restricts the relief in proportion to how much of the R&D was carried out directly by the claimant (or genuinely subcontracted on an arm's-length basis) versus acquired or subcontracted to connected parties.
- Apply the Patent Box deduction formula — reducing the relevant IP profit to an effective 10% tax rate, using a formula that calculates the additional deduction needed to bring the tax rate on that profit down from the main rate to 10%.
Simplified worked example
| Step | Amount |
|---|---|
| Relevant IP profit (after routine return deduction) | £500,000 |
| Nexus fraction (assume 100% — all development done in-house) | 1.0 |
| Qualifying residual profit | £500,000 |
| Tax at standard 25% main rate (without Patent Box) | £125,000 |
| Tax at effective 10% Patent Box rate | £50,000 |
| Tax saving from Patent Box election | £75,000 |
If the nexus fraction were lower — say 0.6, reflecting some development work being subcontracted to a connected overseas entity — only 60% of the £500,000 relevant IP profit (£300,000) would benefit from the 10% rate, with the remaining £200,000 taxed at the standard main rate.
Electing into Patent Box
Patent Box relief is not automatic — a company must actively elect in, generally within a specified time limit after the accounting period the profits relate to. Once elected, the company remains within the regime for subsequent periods unless it actively elects out, so the decision, once made, has an ongoing administrative and reporting commitment attached to it.
Is it worth claiming for a small company?
Patent Box's genuine compliance complexity — profit attribution, nexus fraction calculations, routine and marketing return deductions — means the administrative cost of a claim can be significant relative to the tax saving for companies with only modest patented-product profit. It tends to be most worthwhile where:
- A clearly identifiable, substantial profit stream flows from products incorporating the qualifying patent.
- The company genuinely carried out (or properly subcontracted) the underlying development itself, avoiding a heavily restricted nexus fraction.
- The ongoing compliance cost is proportionate to the recurring tax saving expected across multiple future accounting periods, not just a one-off benefit.
Use our corporation tax calculator to compare your standard tax liability against an illustrative Patent Box-adjusted position for profit attributable to qualifying patented products.
Frequently asked questions
What is the Patent Box effective tax rate?
Profit attributable to qualifying patents (and certain other qualifying IP rights) is taxed at an effective rate of 10%, compared with the standard 25% main rate of corporation tax (or 19% small profits rate).
What qualifies as a Patent Box patent?
Patents granted by the UK Intellectual Property Office, the European Patent Office, and certain other approved European national patent offices qualify, along with certain other IP rights such as supplementary protection certificates and specific plant variety rights.
Do I need to own the patent to claim Patent Box relief?
You need to hold a qualifying licence or ownership interest, and importantly you (or your group) must have undertaken qualifying development activity on the patented invention — simply owning a patent without genuine development involvement is not sufficient under the 'nexus' rules.
How is the qualifying profit calculated?
The calculation is complex, broadly starting from total company profit, then identifying the proportion attributable to qualifying IP income (patented products, licence royalties, and infringement income), before applying a 'nexus fraction' that restricts relief based on how much of the underlying R&D was carried out by the claimant itself versus acquired or subcontracted to connected parties.
Is Patent Box relief worth claiming for a small company with one patent?
It depends on the scale of profit attributable to the patented product. The compliance cost of the nexus fraction calculation and profit attribution can be significant, so Patent Box tends to be most worthwhile for companies where patented products generate substantial, clearly identifiable profit.
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