The Hidden Rule That Could Void Your R&D Tax Claim: Claim Notification Form (CNF) Explained

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If you’re a UK business planning to claim UK R&D tax credits, there’s a critical rule you cannot afford to miss. For accounting periods started on or after 1 April 2023, a new requirement from HMRC, the Claim Notification Form(CNF), could void your R&D tax relief claim if not submitted on time.

In this post, we’ll break down what the CNF is, who it applies to, the deadlines, exemptions, and a recent administrative easement that could save your claim if you’ve already missed the deadline.

What Is the Claim Notification Form (CNF)?

The CNF is a mandatory pre-notification to HMRC indicating your company’s intention to make a claim for UK Research and Development (R&D) tax relief. It was introduced to help HMRC combat fraud and error in the R&D scheme.

Without a valid CNF submission (or qualifying exemption), HMRC will reject your R&D claim - no exceptions.

When Did the CNF Rule Come Into Effect?

The rule applies to accounting periods beginning on or after 1 April 2023. That means:

Companies with January or February year-ends: Your first affected year is the 2025 accounting period (starting 1 February or March 2024)
Companies with March–December year-ends: Your first affected year is the 2024 accounting period (starting from 1 April 2023).

CNF Submission Window: When to Notify HMRC

You must submit the CNF within a specific window - from the first day of the period of account to 6 months after the period ends.

“Period of Account” is the time period covered by a company’s financial statements. It is typically 12 months, although it can be any length (e.g., 9 months, 15 months etc.) due to startup/winding up or change in the company’s year-end. However, “accounting period” (which is the time period used for calculating Corporation Tax) is always a maximum of 12 months.

If you’re claiming for a ‘period of account’ that’s 12 months or less, your ‘accounting period’ will usually cover the same time as your ‘period of account’. If you’re claiming for a ‘period of account’ that’s more than 12 months, it will include 2 or more ‘accounting periods’. The claim notification period is the same for all accounting periods.

Examples

For a 12-month period of account ending 31 December 2024
➜ CNF submission window: 1 January2024 – 30 June 2025
For a 15-month period of account ending 30 June 2025 (due to a year-end change)
➜ CNF submission window: 1 January2024 – 31 December 2025

Plan ahead, once this window closes, your claim could be voided unless you meet an exemption or qualify for HMRC’s recent easement.

Who Must Submit a CNF?

A CNF is required if any of the following apply:

You are a first-time R&D tax credit claimant
You haven’t made a valid claim in the last 3 years
Your last claim within 3years was rejected by HMRC

Understanding the 3-Year “Look-Back” Rule

This period ends on the last day of your CNF deadline.

Example: If your accounting period ends 31 December 2024, the CNF deadline is 30 June 2025. The look-back period covers 1 July 2022 – 30 June 2025.

But beware:

Claims made for periods starting before 1 April 2023, submitted via amended returns after 1 April 2023, do not count as valid claims for the 3-year look-back.
Only claims for periods starting before 1 April 2023, submitted via the original tax return, or via amended return but the amendment was filed before 1 April 2023, and not rejected by HMRC can count as valid claims for the 3-year look-back; they will then relieve you of the obligation to provide a claim notification.

Real-Life Example

If you claimed for:

FY2020 via an amended return submitted by 31 December 2022 ✔️ Counts as valid
FY2021 via an amended return submitted by 31 December 2023 ❌ Doesn’t count

Since the FY2020 claim counts as a valid one under the 3-year look-back exemption, you don’t need a CNF for FY2024.

But if FY2021 was your only claim in the past 3 years, a CNF is required for claiming tax relief for FY2024, unless your FY2024 claim is filed (either via the original or amended Tax Return) before the CNF deadline.

Avoiding CNF: A Time-Saving Tip

To avoid the CNF hassle in the future, it is advisable to:

Submit your R&D claim before the CNF deadline
Always submit your R&D claim with your original tax return instead of amending it later, which can relieve your next claim period of the CNF requirement

However, this requires accurate forecasting and prompt filing, not always feasible.

What Information Is Required for the CNF?

You’ll need

Company UTR (Unique Taxpayer Reference)
Start and end date of the relevant accounting period
Period of account dates, if different from accounting period
Contact details for:
- The senior officer responsible(e.g., company director)
- Any agents involved in theR&D claim
High-level project overview:
- Project goals
- Why the work meets HMRC’sR&D criteria

📌 Important

Save a copy of the form before submission, you can’t access it afterward.
Company UTR and the accounting period / period of account dates must match the version shown in your Company Tax Return, otherwise HMRC will reject the form.

What Happens After CNF Submission?

You’ll receive an automated confirmation email from HMRC with a reference number. Keep this safe, you’ll need it if you contact HMRC about the CNF.

If you decide not to proceed with your R&D claim, no further action is required.

If you do proceed, submit your claim via the Company Tax Return.

Missed the Deadline? HMRC’s Easement Might Save Your Claim

Great news: HMRC has acknowledged confusion over their previous guidance and is offering a temporary reprieve for affected companies.

What Went Wrong?

According to HMRC's recent RDCF updates, they have failed to clearly state that amended returns submitted after 1 April 2023 for periods starting before that date wouldn’t count towards the 3-year look-back.

Between 8 September and 17 October 2024, this caused many companies to skip the CNF for their FY2024 claim, in error.

Who Qualifies for Relief?

You may still be able to claim R&D relief for FY2024 without the CNF if:

You submitted an amended return (with a previous R&D claim) between 1 April 2023 and 30 November 2024 inclusive; and
Your FY2024 CNF deadline was between 8 September and 30 November2024.

How to Apply

Email randd.policy@hmrc.gov.uk with the subject: “CIRD183000 notification” and include:

Company name & UTR
Date of amended return submission (with the R&D claim included)
Accounting period not notified due to HMRC’s guidance error
Period of account for the above accounting period

If using an agent, include proof of authority. HMRC will review and invite eligible companies to proceed with claims.

If your accounting period ended between March and May 2024 and you didn’t pre-notify, check your records. You might still be able to secure your R&D tax relief.

Final Thoughts: Navigating the CNF with Confidence

The CNF is a critical step in securing your R&D tax relief, but its rules (from deadlines to exemptions) can be complex. Miss the deadline or get the details wrong, and your entire R&D tax claim could be rejected.

At ResearchQX, we specialise in UK R&D Tax Credit claims and ensure our clients remain fully compliant with HMRC’s evolving rules, including CNF and Additional Information Form (AIF) submissions.