Ireland gives 12 months from the end of the accounting period to claim, which is the shortest claim window among the seven countries after the Australian registration rule, and it adds a notification step for companies that have not claimed recently. The two interact: a company that must notify has, in practice, 9 months from the period end to do so. This page sets out the dates, what can be amended and a calendar for a 31 December year end.
Registration and notification
There is no registration. Companies claiming for the first time, or that have not claimed in the previous 3 years, must notify Revenue in advance, at least 90 days before the claim, using a prescribed form. The 3 years are measured by accounting periods: a company that claimed for any of the 3 accounting periods before the current one is exempt. The notice is a condition of a valid claim: without it, Revenue will not accept the claim for the period.
Because the claim must be made within 12 months of the period end and the notice at least 90 days before the claim, the latest safe date for the notice is 9 months after the period end, which coincides with the ordinary return filing date. Companies that leave the credit until the return is prepared can find the notice window already closed.
Claim deadline
| Item | Deadline | Late? |
|---|---|---|
| Pre-filing notification | At least 90 days before the claim, if required | No; a claim without it is invalid |
| Preliminary corporation tax | One instalment in the 11th month for small companies; two instalments for large companies | Interest |
| Form CT1 | By the 23rd day of the 9th month after the end of the accounting period, filed electronically | Surcharge on late filing and restriction of reliefs |
| R&D credit claim | Within 12 months of the end of the accounting period in which the expenditure was incurred | No. No late claims |
| Amended claim | Within the same 12 months | No |
| Second and third instalments | Claimed on the returns for the following two accounting periods | Each within its own 12 month window |
| Records | 6 years | Not applicable |
The 12 month limit is absolute. Revenue has no discretion to extend it, and the claim must be complete and correct within it: an understated claim cannot be increased after the window closes, though it can be reduced.
Amendments and late claims
Within 12 months. The claim can be made, increased or corrected by amending the Form CT1 through Revenue Online Service. The instalment elections can also be revisited within the window.
After 12 months. No claim or increase. A company that discovers qualifying work after the window has lost the credit for that period, although the expenditure remains deductible in the ordinary way.
Revenue amendments. Revenue can amend an assessment within 4 years of the end of the accounting period in which the return was filed, and without limit where the return was not full and true. A Revenue intervention that reduces the credit leads to repayment of instalments already paid, with interest.
Instalment timing. The second and third instalments are not automatic: each is claimed in the return for the following period, and the offset or repayment election is made at that point. A company that fails to file those returns on time delays its own instalments.
Calendar for a typical year end
For a hypothetical company, Lee Valley Software Limited, with an accounting period ending 31 December 2025, claiming for the first time.
| When | What happens |
|---|---|
| January to December 2025 | R&D carried on; project records and timesheets kept |
| By 23 June 2026 | Pre-filing notification filed, giving at least 90 days before the planned claim |
| By 23 September 2026 | Form CT1 filed with the credit claim and the instalment election; first instalment follows |
| By 31 December 2026 | Last date to make or amend the claim for 2025 |
| By 23 September 2027 | 2026 return filed, claiming the second instalment |
| By 23 September 2028 | 2027 return filed, claiming the third instalment |
| To end of 2030 | Revenue's 4 year amendment window on the 2026 return |
| To end of 2031 | Records retained |
Companies that have claimed in each of the previous 3 periods skip the notification and can file the claim with the return in September.
Common questions
We claimed 4 years ago but not since. Do we need to notify? Yes. The exemption needs a claim in one of the 3 accounting periods immediately before the current one.
Can we claim for last year as well? Only if its 12 month window is still open.
Does a Revenue audit stop the clock? No. The 12 month limit runs regardless.
Our accounting period is 15 months. How do the dates work? A period of account longer than 12 months is split into two accounting periods for corporation tax, each with its own return, claim and 12 month window, and the notification rule is tested for each.
Can the instalments be accelerated? No. The second and third instalments are claimed in the following two periods' returns and cannot be brought forward.
Related pages
Official sources
Educational content only, not tax advice. See the disclaimer.