What Is the Deadline to Submit an R&D Tax Credit Claim?

The deadline to submit an R&D tax credit claim is two years from the end of your accounting period. But for some companies, that is not the only date they need to track.

The Advance Notification Form (ANF) introduces an earlier deadline for first-time claimants and for businesses that have not claimed in the last three years; miss it, and your claim is invalid before it has even started.

This article sets out the full picture: the core two-year deadline, the ANF requirement, what you need to prepare, and how much time it realistically takes to get a claim to submission.

What is the deadline to submit an R&D tax credit claim?

The deadline to submit a claim is two years after the end of the accounting period you are claiming for. This deadline applies to every company, regardless of size or scheme.

Here is what that looks like in practice:

Company A has an accounting period running from 1 April 2024 to 31 March 2025. The two-year deadline for submitting its R&D tax credit claim falls on 31 March 2027.

The claim is made through your Company Tax Return (CT600), which must be filed with HMRC by the deadline. You can submit your claim either with your original CT600 or in an amended return.

Before you can submit the CT600, you are also required to submit the Additional Information Form (AIF), which must be filed first. The AIF has no separate deadline of its own, but it must come before the CT600; if you file the CT600 without a valid AIF, the claim will not be accepted and you will need to resubmit.

This deadline does not change for extended or shortened accounting periods. However, if your accounting period is extended, you will need to submit an AIF for the initial 12-month period and another for the shortened remaining period.

Two years sounds generous. In practice, given what is required to prepare a robust claim, many companies find the window shorter than expected.

Does the Advance Notification Form change your deadline?

For some companies, yes. The Advance Notification Form (ANF) is an earlier, separate requirement that applies to:

• Companies claiming R&D tax relief for the first time
• Companies that have not made an R&D tax claim in the previous three years

The ANF deadline is six months after the end of the period of account. That means, for a company with a 31 March accounting period end, the ANF must be submitted by 30 September of the same year, well before the two-year claim deadline.

Company B has an accounting period running from 1 April 2024 to 31 March 2025. It has not claimed R&D tax credits before. The ANF must be submitted by 30 September 2025. The claim itself can follow any time up to 31 March 2027.

Miss the ANF deadline, and your claim for that period is invalid. There is no late submission option. If you are a first-time claimant or are returning to the scheme after a gap, this is the date that should be in your calendar first.

Myriad has developed the UK's first Advance Notification Form Checker so you can confirm whether the ANF applies to you and, if so, exactly when your deadline falls.

What does submitting a claim actually involve?

A valid R&D tax credit claim requires more than completing the CT600. Before submission, you need to prepare the Additional Information Form, which requires you to describe each qualifying project in structured detail: the field of science or technology, the baseline knowledge, the advance you sought to achieve, the uncertainties you faced, and how you worked to resolve them. You also need to provide a breakdown of qualifying costs by category and by project.

For most claims, the technical narrative is the most time-consuming element, particularly for companies with multiple projects across different teams. Cost attribution, especially for staff time spread across R&D and non-R&D work, is where errors most commonly occur.

It is also a good moment to consider whether a supplementary technical report should be prepared alongside the AIF. HMRC does not require one, but a well-prepared report, submitted with the CT600, demonstrates robustness and often reduces the risk and burden of a compliance check later. Similarly, you should make sure you have strong record-keeping practices so you can prove any aspect of your claim to HMRC in the event of a compliance check.

How long does it take to prepare a claim?

For a straightforward claim covering a small number of projects, a DIY approach typically takes around 10-15 hours across a few days or weeks. That figure rises quickly with the number of projects and their complexity, particularly where cost apportionment across staff and departments is involved. For companies with 3 or more projects, or significant subcontractor and externally provided worker costs, the time required can be considerably higher.

Using a specialist adviser, whether full consultancy like Myriad or a guided software service, reduces the internal time burden. With full consultancy, the adviser handles technical interviews, writes the project narratives, prepares the cost breakdown, submits the AIF, and manages correspondence with HMRC. Your team is still required to provide information and review the output, but the hours required internally are materially lower than a DIY approach.

You can read more about how to choose the right adviser approach for you here: Should I Use a Consultant, Software, Or DIY My R&D Tax Credit Claim?

Worth noting: even with professional support, leaving the process late increases risk. Your team will still need to provide accurate information, and leaving your claim until the two-year deadline makes this harder to find or remember, adding onto the time it takes to prepare a claim.

What happens if you miss the deadline?

If you miss the two-year deadline for submitting your CT600, the claim cannot be made. There is no mechanism for a late submission. You lose the relief for that period entirely.

The same applies to the ANF. If you are a qualifying first-time claimant and you do not submit the ANF within six months of your period of account end, the claim for that period is invalid, regardless of whether your R&D activity is otherwise genuine and eligible.

Key takeaways

• The main claim deadline is two years after the end of your accounting period. This is when your CT600, original or amended, must be filed.
• The AIF must be submitted before the CT600. There is no separate AIF deadline, but it must precede the return.
• The ANF applies to first-time claimants and those who have not claimed in the past three years. The ANF deadline is six months after the end of the period of account, which is considerably earlier than the two-year claim window.
• Missing the ANF deadline invalidates the claim for that period. There is no late submission option.
• Preparation takes time. Even a small claim takes around 15 hours to DIY; complex, multi-project claims take considerably longer. Starting early is not just good practice; it is the difference between a robust claim and a rushed one.

If you are approaching a deadline or are uncertain whether the ANF requirement applies to you, don't leave it to chance. Contact Myriad to discuss your specific situation.