Should You Wait to Make Your R&D Tax Claim? Timing and Deadlines Explained

An R&D tax credit claim can be submitted any time up to two years after the end of your accounting period. That flexibility gives many claimants room to relax. But, in practice, waiting rarely improves a claim, and for some companies it can invalidate one entirely before a single figure has been submitted.

This article sets out the two deadlines you need to know, how long preparation actually takes, why businesses delay, and whether there is ever a genuine benefit to waiting.

What are the deadlines for R&D Tax Credits?

There are two dates that matter; you must meet both to be able to make a claim.

The claim deadline

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

The claim is made through your Company Tax Return (CT600), either your original return or an amended one, and must be preceded by a valid Additional Information Form (AIF) setting out the technical detail of each project. If the CT600 is filed without a valid AIF, the claim will not be accepted.

The ANF deadline

The Advance Notification Form (ANF) is a separate, earlier requirement. It applies if you are claiming for the first time, or if you have not made an R&D tax claim in the previous three years.

The deadline is six months after the end of your period of account, well before the two-year claim window, and there is no late submission option.

Company B has an accounting period running from 1 April 2025 to 31 March 2026. It has never claimed R&D tax relief before. Its ANF deadline is 30 September 2026, six months after the end of their accounting period. If Company B decides in November 2026 that it wants to claim, the deadline has already passed and the claim for that period cannot be made, regardless of how genuine the underlying R&D was.

Myriad's Advance Notification Form Checker confirms whether the ANF applies to you and, if so, exactly when your deadline falls. It is worth checking as soon as your accounting period ends, not months later.

You can submit an ANF even if you’re not certain that you’ll actually make a claim, so it’s worth getting this out the way if you’re thinking about R&D tax relief.

How long does it take to prepare a claim?

There is no fixed answer; preparation time depends far more on your team's availability than on the complexity of the claim itself. A straightforward claim with a small, cooperative technical team can be turned around in under a week. A claim spanning multiple projects, with staff time to book in for interviews and cost data to pull together across departments, can reasonably take several months from first conversation to submission.

Our R&D tax relief claims process sets out what that timeline looks like in practice: eligibility scoping, building the technical report, financial analysis and cost calculation, then submission. We won’t let a timing choice become a missed deadline; HMRC's submission windows are fixed, and starting the process only once you are close to one removes your flexibility to do it properly.

This is the practical argument against waiting. The two-year window looks generous until you work backwards from how long preparation takes and how much of that time depends on people being available.

Why do businesses wait?

There are usually a handful of reasons a claim gets pushed back, and most of them feel reasonable at the time.

• Uncertainty about eligibility. The company is not sure its projects qualify as R&D and gathering evidence takes time and drops off the priority list.
• Competing priorities. Year-end accounts, audits, and other filing deadlines take precedence, and the R&D claim gets treated as something to return to later.
• Waiting for a "quieter" period. Technical and finance staff are stretched, and the claim is deferred until there is capacity to do it properly.
• Assuming two years is generous. With a two-year window, there is a natural instinct to treat month 20 the same as month 2.

Are there any benefits to waiting?

In a limited sense, yes. Some delays are legitimate and can strengthen a claim rather than weaken it.

• Finalised accounts. Waiting for year-end figures to be confirmed means your qualifying cost calculation is built on final numbers rather than estimates that need revisiting.
• Corporate restructuring. If a merger, acquisition, or group reorganisation is in progress, it may not be clear which entity should claim until the structure settles.
• Scheme eligibility. Following the move to the merged R&D scheme and the Enhanced R&D Intensive Support (ERIS) scheme for loss-making, R&D-intensive SMEs, the rules and rates that apply depend on your accounting period start date. Taking time to confirm which scheme you fall under is worthwhile.

There is also a specific financial scenario worth addressing directly, since it is sometimes cited as a reason to wait. If you pay your Corporation Tax liability in full and then submit an amended return later to include your R&D claim, you can receive the benefit as a cash credit back from HMRC. On the surface, that can look like an advantage: a lump sum landing after the fact.

In practice, it isn't one. The same benefit, or a larger one in cash flow terms, is available sooner by including the claim in your original return and simply reducing the Corporation Tax liability you pay in the first place. Paying the full amount and waiting to reclaim it ties up cash you didn't need to pay out, for no additional benefit. There is no scenario where deliberately delaying the claim to trigger a repayment outperforms getting it right the first time.

What are the problems with waiting?

Beyond the ANF deadline, which can expire long before most companies think to check it, ongoing delay carries several costs that compound the longer a claim is left.

• Evidence degrades. The technical narrative HMRC expects, the scientific or technological uncertainty you faced, the baseline knowledge you started from, how you tried to resolve it, often relies on people remembering what they did and why. Developers change roles, projects get archived, and contemporaneous notes get harder to reconstruct the longer you leave it. A claim written twelve months after the work is materially thinner than one written three months after.
• Cash flow benefit is delayed. Whether your claim reduces your Corporation Tax bill or results in a payable credit, that benefit only arrives once the claim is submitted and processed. Waiting an extra six months to submit adds six months directly onto when you see the money.
• Compliance risk does not shrink with time. HMRC risk-assesses every claim, and rushed, late-stage claims prepared under deadline pressure are more likely to contain the kind of inconsistencies that draw scrutiny. If a claim is selected for a compliance check, having weak or incomplete records because the claim was rushed makes that process considerably harder to manage.
• Your options narrow. The closer you get to the two-year deadline, the less room you have to fix problems if the technical narrative needs more detail, if cost data is missing, or if a member of staff you need to speak to has left. Starting early keeps those options open.

Key takeaways

• There are two deadlines, not one. The two-year claim deadline applies to everyone; the six-month ANF deadline applies to first-time claimants and those who haven't claimed in the past three years.
• Preparation time depends on your team, not the calendar. Claims can take anywhere from a week to several months depending on availability, so the two-year window is not as generous as it looks.
• Some delay is legitimate. Finalising accounts, resolving a restructuring, or confirming scheme eligibility are reasonable grounds to wait.
• The problems with waiting outweigh the perceived benefits. Evidence weakens, cash flow benefit is delayed, and your room to fix issues narrows the closer you get to the deadline.

If you are unsure whether the ANF applies to your business, or you are weighing up when to start your claim, don't leave it to chance. Contact us to discuss your specific situation.