Ireland CT1 for November Year-Ends: Four Days to 23 August ROS

Revenue’s calendar of key dates for tax professionals lists corporation tax returns for accounting periods ending between 1 and 30 November 2025 in the 1–23 August 2026 window for electronic filers, with balance payments on the same timetable. Where the return and payments are not received electronically, the filing date is 1–21 August. As of 19 August, ROS filers have four days — including the weekend — to submit Form CT1 and pay any balance due.

The same August cluster also covers preliminary tax for accounting periods ending 1–30 September 2026, July RCT on 23 August, and third-party information returns for November 2025 year-ends through month-end. Do not let a completed July VAT 3 distract from these corporation tax packs.

What must be review-ready by 23 August

Lock iXBRL financial statements, Form CT1 computations, and any close-company or relief elections that must travel with the return. Confirm ROS payment methods early if you need the electronic due date — filing alone or paying alone does not unlock the ROS extension where both are required.

Companies with December year-ends are not in this window; their CT1 lands on 23 September 2026. Mixing the two diaries is a common August error when finance teams run multiple year-ends in parallel.

Action checklist for the next four days

Confirm every November 2025 accounting period company on the ROS worklist and name an owner for CT1 and payment.

Reconcile corporation tax paid on account against the final computation before the balance payment leaves the bank.

Diary July RCT (23 August) and IOSS (31 August) separately so cash-tax items do not steal the CT1 review slot.

Queue December year-end CT1 work for September after these packs clear — do not start that five-week runway by abandoning November filings.

How FinnAccountings helps before ROS day

Export-ready ledgers shorten the last four days of CT1 review. FinnAccountings helps Ireland and UK companies and advisers prepare bookkeeping and tax packs with Chartered Accountant insight before you or your Chartered Accountant (Ireland) or ICAEW/ACCA adviser files. Start a free trial for review-ready drafts — we prepare records; we do not file CT1 through ROS on your behalf.

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Related reading

Use the four-day PAYE, RCT, and CT cash checklist for the wider 23 August ROS cluster.

Ireland PAYE, RCT and CT: four days to 23 August →

September AP preliminary tax still runs through 23 August — keep that pack beside CT1.

Ireland CT preliminary tax for September APs →

December year-end companies can start the longer runway to 23 September after this week clears.

Ireland CT1 countdown for December year-ends →