Corporation Tax deadlines for Irish limited companies

Corporation Tax for an Irish LTD is not “pay something in November and forget it.” Payment and return dates hang off your accounting period. Directors who only remember the personal tax year keep discovering CT deadlines in the wrong month.

This article is about the operating rhythm: what to put on the calendar, when preliminary tax bites, and how to avoid underpayment interest while the return is still being finalised.

Start from accounting year‑end — always

Your CT clock starts at the end of the accounting period. Change year‑end and you rewrite the payment and filing map. When you incorporate, or when you change ARD/year‑end with advice, update three artefacts the same week: ROS profile awareness, the company calendar, and whoever prepares CT1.

• Year‑end date → drives preliminary tax timing.
• Preliminary tax → often due before the return is complete.
• CT1 filing window → its own deadline after the period ends.

Preliminary tax without the folklore

Small companies can use rules of thumb for preliminary tax (including prior‑period bases in the right conditions). The folklore version is “pay whatever and true‑up later.” The operational version is: know which basis you are using, diary the payment date, and leave headroom if profits jumped.

Underpaying preliminary tax is how quiet interest appears. Overpaying ties up cash. The middle path is a dated estimate, a calendar alert at 30 / 14 / 7 days, and a named owner (director or accountant) for the ROS payment.

CT1 is a project, not an evening

Form CT1 via ROS needs accounts, computations, and decisions that rarely fit into one Sunday night. Work backwards from the filing deadline: draft numbers → review → ROS upload → submit. Put the review meeting on the calendar before the hard deadline, not on it.

Monthly habit that actually helps

• Keep management accounts close enough that CT estimates are not fiction.
• Once a quarter, glance at open CT items next to VAT and payroll dates.
• After any year‑end change, rebuild the CT map before the next period closes.

Taxee.pro calculates Irish filing deadlines from your company profile so CT sits beside VAT, PAYE, and CRO — one timeline instead of scattered accountant emails.