Ireland September 2026 Tax Deadlines: PAYE, Bi-Monthly VAT, CT1 and RCT for SMEs

While August 2026 still has open ROS dates, Irish employers, VAT-registered traders, and company directors should lock September into the same diary. Revenue’s Calendar of key dates for tax professionals lists PAYE/PRSI/USC/LPT for August on 14 September, a dense VAT 3 cluster on 19 September (including the July–August bi-monthly return), and Corporation Tax plus RCT obligations through the 23rd.

Planning the September sequence now reduces the scramble after mid-August PAYE, VAT 3, RCT, and CT preliminary windows clear. Use this checklist beside the live August SME deadlines briefing — do not skip remaining August ROS work.

By 14 September 2026, employers must file and pay the monthly PAYE/PRSI/USC/LPT return for August 2026. Revenue extends the payment date to the 23rd for ROS users who file and pay online — paper or non-electronic filers do not get that extension.

The same 14 September date covers Dividend Withholding Tax (DWT) return and payment for August 2026, and the F30 monthly return and payment for Professional Services Withholding Tax (PSWT). Treat payroll, dividends, and professional services withholding as one mid-month cluster rather than three separate surprises.

Monthly VAT 3 for the August period (plus Return of Trading Details where the VAT accounting period ends in August) is due 19 September 2026. Bi-monthly traders file July–August 2026 on the same date, with RTD where the VAT accounting period ends between 1 July and 31 August.

Four-monthly VAT 3 for May–August 2026 and annual VAT 3 for the September–August cycle (where the VAT accounting period ends in August) also land on 19 September. Confirm your filing frequency in ROS before you lock figures — bi-monthly July–August is the busiest September VAT pack for many SMEs after the 19 August July monthly return.

Corporation Tax preliminary tax for accounting periods ending 1–31 October 2026 sits in the 1–23 September electronic window (1–21 if not electronic). The same window covers CT1 returns and balances for accounting periods ending 1–31 December 2025 — the nine-month deadline many calendar-year companies diary as 23 September.

Relevant Contracts Tax monthly return and payment for August 2026 is due 23 September 2026. Third-party information returns for December 2025 CT periods run through 1–30 September. IOSS monthly VAT for August is listed for 30 September where that scheme applies.

Organised payroll, VAT, and period-close ledgers make September ROS sessions faster to review. FinnAccountings helps Ireland and UK businesses 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 PAYE, VAT 3, CT1, or RCT returns to Revenue on your behalf.

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Finish August first — PAYE, VAT 3, RCT, and CT preliminary windows still sit on this month’s Revenue calendar.

Ireland August 2026 tax deadlines for SMEs →

December year-end companies should keep the focused 23 September CT1 countdown beside this month-wide checklist.

Ireland CT1 countdown: 23 September 2026 →

September year-end companies still closing August CT preliminary tax should use the dedicated 23 August window briefing.

Ireland CT preliminary tax: nine days to 23 August →

Use the dual-market VAT calculator for Ireland and UK rate scenarios before you lock September VAT 3 figures.

Open free VAT calculator (Ireland & UK) →