Name: OpenAccountants MCP Server
Author: OpenAccountants

Section 1 -- Quick reference

Quick reference table

Field	Value
Country	Ireland
Tax	Preliminary income tax (income tax + USC + PRSI Class S)
Primary legislation	TCA 1997, Part 41A (Self-Assessment), ss. 952-959
Supporting legislation	TCA 1997, s.1080 (interest), s.1084 (surcharges); Finance Acts
Authority	Revenue Commissioners (Revenue)
Portal	ROS (Revenue Online Service)
Currency	EUR only
Payment schedule	Annual lump sum: 31 October (paper) or ~14 November (ROS)
Safe harbours	100% of prior year liability OR 90% of current year liability
De minimis	Prior year liability <= EUR 200: no preliminary tax required
Components	Income tax + USC + PRSI (Class S at 4.125%)
CGT	Separate payment dates (15 Dec / 31 Jan) -- NOT part of preliminary tax
Contributor	Open Accountants Community
Validated by	Pending -- requires validation by Irish Chartered Accountant or CTA
Validation date	Pending

Key dates (tax year 2025)

Event	Paper deadline	ROS deadline
Pay 2025 preliminary tax	31 Oct 2025	~14 Nov 2025
File 2024 Form 11	31 Oct 2025	~14 Nov 2025
Pay 2024 balance of tax	31 Oct 2025	~14 Nov 2025

Conservative defaults

Ambiguity	Default
Rule selection unclear	Use 100% of prior year (safe, no estimation needed)
Filing method unclear	Confirm paper vs ROS (2-week difference in deadline)
CGT included in preliminary	EXCLUDE -- separate dates
First year of self-assessment	Must use 90% rule (no prior year available)
Prior year liability unknown	STOP -- the 100% rule requires prior year figure

Section 2 -- Required inputs and refusal catalogue

Required inputs

Minimum viable inputs — prior year final tax liability (income tax + USC + PRSI) for the 100% rule, OR current year estimated income for the 90% rule.
Recommended inputs — filing method (paper vs ROS), PAYE credits from employment, CGT obligations (separate), current year income expectations.
Ideal inputs — complete prior year Form 11, Revenue assessment, current year P&L projection, PAYE certificates.
Refusal policy if minimum is missing — HARD STOP for 100% rule. Without prior year liability, the 100% rule cannot be computed. For 90% rule, current year estimates needed.

Refusal catalogue

R-IE-PT-1 -- Trust/corporate preliminary tax — Trigger: client asks about corporate or trust preliminary tax. Message: "This skill covers self-employed individuals only."
R-IE-PT-2 -- CGT computation — Trigger: client asks about CGT preliminary tax computation. Message: "CGT has separate payment dates (15 December / 31 January) and is NOT part of the 31 October preliminary tax payment. CGT computation is outside this skill."
R-IE-PT-3 -- Non-resident self-assessment — Trigger: non-resident client. Message: "Non-resident self-assessment is outside this skill."

Section 3 -- Payment pattern library

This is the deterministic pre-classifier for bank statement transactions. When a debit matches a pattern below, classify it as a preliminary tax payment.

3.1 Revenue preliminary tax debits

Revenue preliminary tax debits

Pattern	Treatment	Notes
REVENUE, REVENUE COMMISSIONERS	Preliminary tax payment	Match with October/November timing
ROS PAYMENT, ROS DEBIT	Preliminary tax payment	ROS online payment
PRELIMINARY TAX, PRELIM TAX	Preliminary tax payment	Explicit description
FORM 11, SELF ASSESSMENT	Preliminary tax or balance payment	Distinguish by timing
INCOME TAX REVENUE	Preliminary tax payment	Generic description

3.2 Timing-based identification

Timing-based identification

Debit date range	Likely payment	Confidence
15 October -- 5 November	Preliminary tax (paper deadline 31 Oct)	High if Revenue payee
1 November -- 20 November	Preliminary tax (ROS deadline ~14 Nov)	High
Same date: large single debit	Combined: balance of prior year + current year preliminary	Flag for reviewer to split

3.3 Related but NOT preliminary tax

Related but NOT preliminary tax

Pattern	Treatment	Notes
CGT, CAPITAL GAINS TAX	EXCLUDE	Separate obligation, separate dates
PAYE, EMPLOYER PAYE	EXCLUDE	Employer PAYE payment
VAT, VAT3 RETURN	EXCLUDE	VAT payment
PRSI EMPLOYER	EXCLUDE	Employer PRSI
LOCAL PROPERTY TAX, LPT	EXCLUDE	Property tax
USC DIRECT	EXCLUDE	USC coded through employment
SURCHARGE, INTEREST REVENUE	EXCLUDE	Penalty/interest

3.4 Direct debit identification

Direct debit identification — If the client pays preliminary tax by direct debit instalments (105% of pre-prior-year rule), monthly debits to Revenue throughout the year are direct debit preliminary tax payments. Flag for reviewer.

Section 4 -- Worked examples

Example 1 -- Standard 100% rule

Input: Prior year final liability = EUR 15,000 (income tax EUR 9,000 + USC EUR 3,500 + PRSI EUR 2,500).

Output: Preliminary tax = EUR 15,000. Due 31 Oct (paper) or ~14 Nov (ROS).

Example 2 -- 90% rule, income drop

Input: Prior year liability = EUR 30,000. Current year estimated liability = EUR 10,000.

Output: 90% rule: EUR 10,000 x 90% = EUR 9,000. Saves EUR 21,000 vs 100% rule. Risk: if actual > estimate, interest applies on shortfall.

Example 3 -- First year of self-employment

Input: First year, no prior year self-assessed liability. Estimated income EUR 60,000. Estimated tax: IT EUR 11,000 + USC EUR 2,400 + PRSI EUR 2,400 = EUR 15,800.

Output: 90% rule (only option). Preliminary = EUR 15,800 x 90% = EUR 14,220.

Example 4 -- De minimis

Input: Prior year liability = EUR 120.

Output: Below EUR 200 de minimis. No preliminary tax required. Still must file Form 11.

Example 5 -- CGT separate payment

Input: Income preliminary EUR 12,000 (due 31 Oct). CGT on June disposal = EUR 8,250.

Output: Income preliminary: EUR 12,000 due 31 Oct. CGT: EUR 8,250 due 15 Dec. Two separate payments.

Example 6 -- Bank statement classification

Input line: 31.10.2025 ; REVENUE COMMISSIONERS ROS ; DEBIT ; PRELIMINARY TAX 2025 ; -15,000.00 ; EUR

Classification: Preliminary tax for 2025. Tax payment -- not a deductible expense.

Section 5 -- Computation rules

5.1 Two safe harbour rules

Two safe harbour rules

Rule	Amount	When
100% of prior year	100% of prior year final liability	Safe default -- no estimation needed
90% of current year	90% of current year estimated liability	If current year significantly lower

Safe harbour compliance — Taxpayer meets obligation if they pay at least ONE of these amounts.

5.2 What constitutes "tax liability"

Definition of tax liability — Preliminary tax = income tax + USC + PRSI (Class S at 4.125%). PRSI minimum = EUR 650 if income > EUR 5,000.

5.3 Computation steps

Computation steps — prior_year_liability = income_tax + USC + PRSI option_A = prior_year_liability x 100% option_B = estimated_current_year_liability x 90% preliminary_tax = min(option_A, option_B) (or simply pay option_A for safety) net_due = preliminary_tax - PAYE_credits - withholding_tax

5.4 105% of pre-prior-year (direct debit)

105% direct debit rule — For clients on direct debit: 105% of the pre-prior-year liability, spread in equal monthly instalments. This is a third safe harbour.

5.5 First year rule

First year rule — First year of self-assessment: 100% rule is unavailable (no prior year). Must use 90% of estimated current year.

Section 6 -- Penalties and interest

6.1 Interest on late/insufficient payment

Interest on late/insufficient payment

Element	Rate
Daily rate	0.0219% per day
Approximate annual rate	~8% per annum
Runs from	Due date to actual payment date

6.2 Surcharge for late return filing

Surcharge for late return filing

Delay	Surcharge
Within 2 months of deadline	5% of tax due (max EUR 12,695)
More than 2 months late	10% of tax due (max EUR 63,485)

Surcharge applies to return not payment — The surcharge applies to the RETURN, not the payment. Even if payment is on time, a late return triggers the surcharge.

Section 7 -- PRSI Class S

PRSI Class S parameters

Parameter	Value
Rate	4.125%
Minimum annual contribution	EUR 650 (even if 4.125% < EUR 650)
Applied to	All self-employment income, no upper limit
Exemption	Income below EUR 5,000

PRSI collection method — PRSI is included in the preliminary tax payment and collected through self-assessment.

Section 8 -- Edge cases

De minimis: no preliminary tax. Must still file Form 11.

Use 90% rule. Risk: interest if estimate too low.

No prior year liability. Must estimate and pay 90%.

Paper: strictly 31 October. ROS: ~14 November (exact date published annually). Extension ONLY for ROS filers who both file AND pay through ROS.

CGT = gain x 33%. Due 15 December. Separate from 31 Oct preliminary.

Preliminary tax on rental income (Case V). 100% rule on prior year Case V liability. PAYE credits offset income tax.

Monthly spread of 105% of pre-prior-year. Flag for reviewer.

Payment on time but return 6 weeks late: 5% surcharge applies. Surcharge triggered by return, not payment.

Section 9 -- Self-checks

Before delivering output, verify:

Section 10 -- Test suite

Test 1 -- Standard 100% rule

Input: Prior year liability EUR 15,000. Expected: Preliminary = EUR 15,000. Due 31 Oct or ~14 Nov (ROS).

Test 2 -- 90% rule

Input: Prior year EUR 30,000. Estimated current = EUR 10,000. Expected: 90% x EUR 10,000 = EUR 9,000. Interest risk flagged.

Test 3 -- First year

Input: First year. Estimated liability EUR 15,800. Expected: 90% = EUR 14,220.

Test 4 -- De minimis

Input: Prior year liability EUR 120. Expected: No preliminary tax. Must still file Form 11.

Test 5 -- CGT separate

Input: Income preliminary EUR 12,000. CGT EUR 8,250. Expected: EUR 12,000 due 31 Oct. EUR 8,250 due 15 Dec.

Test 6 -- Surcharge

Input: Tax EUR 20,000. Return filed 6 weeks late. Expected: 5% surcharge = EUR 1,000.

Test 7 -- PAYE + self-employment

Input: PAYE salary EUR 50,000. SE income EUR 25,000. Prior year SE component EUR 8,000. Expected: Preliminary = EUR 8,000 (100% of prior year SE portion).

Prohibitions

NEVER tell a client the 100% rule requires estimating current year -- it does NOT
NEVER confuse paper deadline (31 Oct) with ROS deadline (~mid-Nov)
NEVER include CGT in the 31 October payment -- separate dates
NEVER forget USC and PRSI when computing "tax liability"
NEVER ignore the surcharge for late filing -- applies even if payment is on time
NEVER apply the 105% rule without confirming direct debit arrangement
NEVER tell a first-year self-employed person to use the 100% rule -- must use 90%
NEVER ignore the EUR 200 de minimis threshold
NEVER present preliminary tax as final -- balance settled with Form 11

Disclaimer

This skill and its outputs are provided for informational and computational purposes only and do not constitute tax, legal, or financial advice. Open Accountants and its contributors accept no liability for any errors, omissions, or outcomes arising from the use of this skill. All outputs must be reviewed and signed off by a qualified professional (such as a CPA, EA, tax attorney, or equivalent licensed practitioner in your jurisdiction) before filing or acting upon.

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Key figures — Ireland, 2025

The full Guide