R&D Claim Notification Form: June 2026 Deadline — Act Now

If your company has a December 2025 year-end and is making a first-time R&D tax relief claim — or your last R&D claim was made more than three years ago — you face a critical deadline: 30 June 2026. Miss it, and any R&D claim you submit for that accounting period will be invalid. HMRC will automatically reject it. The CNF sits alongside the two-year window for submitting R&D claims — for a full breakdown of all the deadlines involved, see our guide on R&D tax credit claim deadlines.

What is the R&D Claim Notification Form?

The Claim Notification Form (CNF) is a pre-notification requirement introduced as part of the 2023 R&D tax relief reforms. Before you file your R&D claim in your Company Tax Return, you must tell HMRC you intend to make one.

It is a short, standalone form submitted through HMRC's secure portal — separate from both your Company Tax Return and the Additional Information Form (AIF).

Who needs to submit one?

You must submit a CNF for an accounting period if either of the following applies:

• You are a first-time R&D tax relief claimant, or
• Your most recent R&D claim was submitted more than three years before the last day of your claim notification period

Your claim notification period runs from the first day of the accounting period to six months after it ends. For a December 2025 year-end, the claim notification period is 1 January 2025 to 30 June 2026.

You are exempt if you have submitted an R&D claim within that three-year window. There are two important exceptions to this exemption — if either applies, you still need to file a CNF:

• HMRC previously rejected one of your R&D claims by removing it from your Company Tax Return, or
• You claimed R&D relief for an accounting period beginning before 1 April 2023 by amending a tax return submitted on or after 1 April 2023

The three-year window is measured from when the previous claim was submitted to HMRC, not from the accounting period it covered.

(Refs: CIRD183000 and HMRC's CNF guidance)

The June 2026 deadline — who is affected?

The CNF must be submitted within six months of the end of the accounting period to which the claim relates.

For companies with a December 2025 year-end (accounting period ending 31 December 2025), the deadline is 30 June 2026.

Other upcoming deadlines for reference:

• January 2026 year-end → 31 July 2026
• February 2026 year-end → 31 August 2026
• March 2026 year-end → 30 September 2026

If you have a December year-end and are unsure whether your recent claim history triggers the requirement, check now — you have days, not weeks.

What happens if you miss it?

The consequences are severe:

• You cannot make a valid R&D claim for that period
• If you submit a claim anyway, HMRC will automatically amend your tax return to remove it
• There is no appeal mechanism for a missed notification deadline — it is a hard cutoff

This is not a penalty you can pay your way out of. The relief simply becomes unavailable for that period.

What does the form ask for?

The CNF is brief but must be precise. You will need:

• Company UTR — must match your CT600 exactly
• Accounting period dates — start and end date
• Name and contact details of the senior internal R&D contact at your company
• Name of any external agent involved in the claim (e.g. your R&D tax adviser)
• A brief description of the R&D activities undertaken

The UTR and period dates must match your Company Tax Return exactly. If they do not, HMRC will be unable to locate the form and may treat the notification as invalid.

How to submit

Submit via HMRC's secure portal at gov.uk/guidance/notify-hmrc-that-you-plan-to-claim-research-and-development-relief. The form cannot be filed by post or email.

After submission, HMRC issues a digital receipt confirming your notification has been received. Keep this for your records.

For a full walkthrough of what comes next, see our guide on how to submit R&D claims to HMRC correctly, and our R&D pre-notification guide for more background on the reformed claims process.

Don't let this trip you up

The CNF is one of the lesser-known requirements of the reformed R&D regime, but missing it is one of the most irreversible mistakes a company can make. If your December 2025 year-end claim is in progress, confirm your notification status today.

Unsure whether your claim history triggers the requirement? Get in touch with Zest Tax — we can check your position and submit the form on your behalf before the deadline closes.