Still banging the drum: pre-notification for R&D tax relief – how does it work? (Part 1)

Author: Jen Badger Published: 18^th March, 2026

Pre-notification for R&D claims was introduced in 2023, and applies to claims starting on or after 1st April 2023. It is required for any company wishing to claim R&D tax relief that hasn’t claimed before or that hasn’t submitted a claim within the last three years. Around 20% of claims made each year are for first-time claimants and many more will be for companies that haven’t claimed recently, so it affects a large minority of claims submitted each year.

Although the requirement for pre-notification has been in play for over two years, we’re continuing to highlight this requirement wherever we can. Why? Because we’re still seeing firms experiencing trouble understanding and applying the rules, and this is contributing to claims being missed or rejected.

As we hurtle towards the March 2026 deadlines and beyond, we wanted to bring together everything you need to know about claim notification over two blogs – this is part 1. This first blog covers what pre-notification entails and how to fill out the Claim Notification Form (CNF), and the second will focus on best practice and how to ensure no claim is missed.

When should a company submit the CNF?

Companies can notify HMRC of their intention to claim R&D tax relief at any time from the first day of the period of account to six months after the end of the claim period – this is known as the claim notification period. For companies with a period of account longer than 12 months this still applies, meaning that only one CNF is required for these periods of account.

Who needs to submit a CNF?

Submitting a CNF is not mandatory for all claims, but the rules around who does need to submit one are a little complicated. Pre-notification is required if:

The company has never claimed R&D tax relief before or,
The company has not submitted a claim for R&D tax relief in the three years prior to the end of the claim notification period or,
The only claims that the company has submitted within the three years prior to the end of the claim notification period were:
- for periods starting before 1st April 2023, and submitted as amendments to the CT600 after 1st April 2023 or,
- rejected by HMRC and removed from the company tax return.

Although claims for periods starting before 1st April 2023 are now mostly timed out, the amendment rule will continue to impact claims for several years until sufficient time has elapsed that either, all companies have submitted subsequent claims, or none of the amended claims are relevant.

How is the CNF completed and submitted?

The CNF is a relatively simple form accessed through an HMRC portal. To complete it, you need the following information:

The claimant company’s UTR
Contact details of the main R&D contact within the claimant company
Contact details of any agents involved in preparing the claim
The accounting period and period of account start and end dates
A high-level summary of the R&D activities

Can claims be submitted if pre-notification is missed?

No. HMRC will reject claims where a required pre-notification has not been submitted. We are aware of cases where HMRC have been somewhat sympathetic where genuinely exceptional circumstances can be demonstrated, but overall, it’s unlikely that a claim will be accepted if the CNF is missing.

What’s the difference between the AIF and the CNF?

There has been some confusion amongst accountants and advisers about the AIF (Additional Information Form) and CNF, and which is needed when. This has largely cleared up now, but it’s still important to understand the main differences between the two forms, as shown in the table below.

	CNF	AIF
Required for all claims?	No	Yes
Submission deadline	Within six months of the end of the claim period	Before CT600 submission (and within two years of the end of the claim period)
Form length	Short form – high level summary of projects	Longer form – detailed project descriptions required

Beyond these practical differences, the key difference between the AIF and the CNF is their purpose. The AIF was introduced as a way for HMRC to gather additional information about all claims and enable inspectors to more easily identify which claims meet the eligibility criteria. The CNF, on the other hand, was introduced to gather high-level details about claims before submission, allowing HMRC to carry out early interventions where claims are less likely to be eligible.

Alongside this, the form prevents first-time claimants from claiming for two years at once, making these companies less attractive to less ethical R&D tax advisers.

Pre-notification has added another important step to the R&D claims process and missing it can mean a claim cannot proceed.

In our next blog, we’ll look at best practices for managing pre-notification in practice, including the processes accountants and advisers can put in place to ensure deadlines are not missed.

In the meantime, we recently presented a webinar covering the CNF rules, the nuance and grey areas around when pre-notification is required and steps to help mitigate against missed claims. You can watch the full recording by clicking below:

Watch webinar on-demand

With stricter HMRC oversight, accountants and advisers need a process that leaves nothing to chance. WhisperClaims keeps you on track with tailored guidance, risk assessments and expert Advice Line support, helping you submit robust claims and stay confidently on the right side of HMRC.

Book a demo today to find out how we can support you and your firm.

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