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At McGovern Worn we believe the preliminary tax deadline catches out more companies than it should, not because the rules are complicated, but because the date creeps up quietly in the run-up to Christmas. If your company has a 31 December year end, the clock is already ticking towards 23 November 2026, and getting this payment wrong, late, or short can cost you in interest charges that are entirely avoidable.

Why 23 November matters

For companies with an accounting period ending on 31 December, preliminary tax is due by the 23rd of the eleventh month of that accounting period. That means the payment for the year ending 31 December 2026 falls due on 23 November 2026. Miss it, or underpay, and Revenue will apply interest from that date until the shortfall is cleared.

This is separate from your CT1 return and the final balance of tax, which are due by the 23rd of the ninth month after the year end, so for a December year end that means 23 September 2027. Preliminary tax is essentially an advance payment based on your estimate of the year’s profits, paid before the year has even finished.

Small company or large company?

The rules differ depending on the size of your company for corporation tax purposes, and this is where confusion often sets in.

Small companies pay their entire preliminary tax liability in one instalment, by the 23rd of the eleventh month. There is no earlier payment required. Most owner-managed SMEs fall into this category, since the test is based on the company’s tax bill in the prior accounting period being below a modest threshold.

Large companies, by contrast, pay in two instalments. The first instalment is due by the 23rd of the sixth month of the accounting period, and a second instalment follows by the 23rd of the eleventh month to bring the total paid up to the required level. If your company has grown significantly or has a group structure, it is worth checking which category you now fall into, because the test is applied year on year and a company can move between categories.

How much do you actually need to pay?

For most small companies, the safe option is to pay the lower of two figures:

• 90% of the final corporation tax liability for the current accounting period, or

• 100% of the corporation tax liability for the previous accounting period.

Whichever of these is lower is the amount you are required to pay by 23 November. If your profits have risen this year, basing the payment on last year’s figure can actually work in your favour, provided last year’s liability was accurately calculated and paid on time.

A worked example

Say a company expects its corporation tax bill for the year ending 31 December 2026 to come to approximately €50,000, based on management accounts and a realistic profit forecast. Ninety per cent of that figure is €45,000, and that is the amount due by 23 November 2026. The remaining €5,000, plus any adjustment once the accounts are finalised, is paid alongside the CT1 return by 23 September 2027.

If last year’s liability was lower, say €40,000, the company could instead choose to pay that full amount now and settle the balance later, once this year’s figures are confirmed. Either route is acceptable, as long as the chosen figure is met in full and on time.

The cost of getting it wrong

Underpaying preliminary tax, or missing the deadline altogether, triggers interest from the due date until the shortfall is paid. That interest accrues daily, and it applies regardless of whether the underpayment was deliberate or simply the result of an overly optimistic profit estimate made too early in the year. There is no grace period for a genuine miscalculation, so it pays to be realistic rather than overly confident when forecasting.

A quick checklist before 23 November

• Confirm whether your company is classed as small or large for this accounting period.

• Pull together up-to-date management accounts to estimate this year’s profit.

• Calculate 90% of the estimated liability and compare it with 100% of last year’s bill.

• Pay the lower figure through ROS by 23 November 2026.

• Diarise 23 September 2027 for the CT1 return and final balance.

• If your profits have changed significantly mid-year, revisit the estimate before the deadline rather than after it.

Getting preliminary tax right is one of those jobs that takes an hour or two now and saves a headache later. If you would like help confirming your figure, or simply want a second pair of eyes on the calculation before the deadline, the team at McGovern Worn is on hand. Call us on , email gillian_duffy@mcgw.ie, or visit mcgw.ie to arrange a quick review before 23 November arrives.

Disclaimer: This article is based on publicly available information and is intended for general guidance only. While every effort has been made to ensure accuracy at the time of publication, details may change and errors may occur. This content does not constitute financial, legal or professional advice. Readers should seek appropriate professional guidance before making decisions. Neither the publisher nor the authors accept liability for any loss arising from reliance on this material.