November is an important month for Irish companies preparing to meet their Preliminary Corporation Tax obligations. For many businesses with a 31 December financial year-end, the key payment deadline is 23 November 2026.

Understanding how Preliminary Corporation Tax works, how much your company needs to pay and when payment is due can help avoid unnecessary interest charges and support better cash flow planning.

What Is Preliminary Corporation Tax?

Preliminary Corporation Tax is an advance payment towards a company’s Corporation Tax liability for its current accounting period.

Rather than waiting until the final Corporation Tax return is filed, companies are generally required to estimate and pay a portion of their tax liability before the accounting period ends.

The amount and timing of these payments depend on whether the company is classified as a small or large company for Corporation Tax purposes.

Small Companies: November Payment Deadline

Under the rules applicable for 2026, a small company is generally one whose Corporation Tax liability for the previous accounting period did not exceed €200,000.

Small companies normally make one Preliminary Corporation Tax payment, due 31 days before the end of their accounting period, subject to the relevant monthly payment deadline.

For companies with a 31 December 2026 year-end, the ROS payment deadline is 23 November 2026.

Small companies can generally calculate their preliminary payment using either:

• 100% of their Corporation Tax liability for the previous accounting period.

• 90% of their estimated Corporation Tax liability for the current accounting period.

The applicable rules and calculations should be reviewed carefully to ensure the correct amount is paid.

Large Companies: Two Preliminary Tax Instalments

Companies with a previous accounting period Corporation Tax liability exceeding €200,000 are generally classified as large companies.

For accounting periods longer than seven months, these companies normally pay Preliminary Corporation Tax in two instalments.

First instalment: Due by the 23rd day of the sixth month of the accounting period. The payment is based on either 50% of the previous period’s liability or 45% of the current period’s estimated liability.

Second instalment: Due by the 23rd day of the eleventh month, bringing the total preliminary payment to 90% of the estimated Corporation Tax liability for the current accounting period.

For large companies with a 31 December 2026 year-end, the second instalment is due on 23 November 2026.

November is also the first instalment deadline for relevant large companies with a 31 May 2027 year-end.

What Happens If You Miss the Deadline?

Failing to pay sufficient Preliminary Corporation Tax by the relevant deadline can result in interest charges on underpaid tax.

Revenue currently applies daily interest of 0.0219% to late Corporation Tax payments.

Businesses should also remember that Preliminary Corporation Tax is separate from the final Corporation Tax return (CT1), which is generally due nine months after the accounting period ends, by the 23rd day of the relevant month for electronic filing.

How Can Businesses Prepare?

With the November deadline approaching, companies should take the opportunity to review their tax position and cash flow.

Key steps include:

• Reviewing current-year profits and estimated Corporation Tax liabilities.

• Checking whether the company qualifies as a small or large company.

• Confirming the correct preliminary payment amount.

• Ensuring sufficient funds are available before the deadline.

• Arranging payment through Revenue Online Service (ROS).

Accurate financial reporting and regular tax forecasting can help businesses manage their obligations and avoid unexpected tax liabilities.

Need Assistance with Corporation Tax Planning?

At Gallagher Keane, we support Irish businesses with Corporation Tax compliance, tax planning, financial reporting and cash flow forecasting.

Whether you need assistance calculating your Preliminary Corporation Tax liability or preparing for upcoming payment deadlines, our team is here to help.

Get in touch with Gallagher Keane:

Email: info@gallagherkeane.ie
Phone: +353 1 969 5100