Claim notification deadlines: why you should submit (even if you’re not doing R&D yet)
Have you checked whether your company needs to submit a CNF before the deadline?
One of the most important but easily overlooked developments in the UK R&D tax relief regime is the Claim Notification Form (CNF) requirement.
Introduced for accounting periods beginning on or after 1 April 2023, companies intending to make an R&D claim must now notify HMRC of that intention within a strict deadline.
This requirement isn’t just bureaucratic form-filling; missing it can mean losing the right to claim relief on qualifying R&D activity in that period, even if the work would otherwise qualify.
What is a claim notification?
The Claim Notification Form (CNF) is a statutory submission to HMRC that tells them you plan to make a claim for R&D tax relief for a specific accounting period.
It’s not the full claim itself, nor does it require detailed technical or financial information, but it is a precondition for claiming for accounting periods beginning on or after 1 April 2023.
You can submit the CNF online via the Government Gateway, and once received, HMRC will usually confirm its acceptance.
When must the CNF be submitted?
The deadline for submitting the Claim Notification is:
Within six months after the end of the accounting period in which any R&D activity took place.
For example:
If your accounting period ended 31 December 2024, you have until 30 June 2025 to file the CNF. This deadline is much tighter than the Corporation Tax filing deadline and operates independently of when you submit your claim.
Who needs to submit a claim notification?
You must file a CNF if:
- You’re making your first-ever R&D claim …and the accounting period qualifies under the CNF rules.
- You haven’t made an R&D claim in the last three years
If the last qualifying claim (as recognised for CNF purposes) was more than three years before the end of the CNF deadline, you must notify.
There are detailed transitional points about how earlier claims count (e.g., amended returns before April 2023 may not count towards the three-year window), so careful checking matters.
Why this matters, even if you’re not doing R&D now
Here’s the key risk:
The CNF requirement is mandatory where it applies, and missing the deadline generally means HMRC will not accept a later R&D claim for that accounting period, no matter how genuine or high-value the R&D work is.
That applies even if:
The R&D work hasn’t started yet, but could happen later.
You think there won’t be qualifying R&D this year.
You intend to make the claim later (e.g., due to audit cycles or staffing).
Given innovation cycles, it’s common for companies to only recognise qualifying activity after year-end. If that recognition happens after the six-month window has closed, a missed CNF can block the claim even if every bit of work was perfectly eligible.
Filing a CNF doesn’t oblige you to claim. It simply keeps your option open and ensures you comply with HMRC’s statutory timetable.
Common misunderstandings
- Myth: “We don’t need to notify because we have never done R&D.”
Not true. If you might do R&D in the period, or you aren’t sure, filing is a smart pre-emptive step.
- Myth: “We’ll just file the full claim later, that’s enough.”
No – without a valid CNF where required, the claim might be rejected before HMRC even considers the technical eligibility.
- Myth: “Our accountant usually files the CT600 on time – that covers it.”
The CNF deadline runs independently and is not tied to the CT600 filing date.
Practical tips
- Add the CNF deadline to your annual compliance calendar
- Review whether your company might do R&D before the six-month window closes
- If you’re unsure, file the CNF as a precaution – there’s no downside and it protects future claims
The Claim Notification Form is a relatively lightweight submission with significant strategic importance. Missing the CNF deadline can mean losing valuable R&D tax relief, not because of what you didn’t do, but because of what you failed to notify.
Even if you think your company isn’t currently doing R&D, submitting the CNF keeps your options open for the future. Given how often R&D work only becomes clear after the year-end, this is one deadline worth respecting.
Need help?
If you’re unsure whether you need to submit a Claim Notification Form or want free advice and practical help with completing and submitting your CNF, contact us, we’re happy to support you and make sure your submission meets HMRC’s requirements.
