Reference

Glossary of personal-tax terms.

The vocabulary that turns up in tax-authority publications, employer payslips, and adviser correspondence across Ireland, the UK, and the US. Each entry links to longer treatment where one exists.

AITI: Associate of the Irish Taxation Institute. The original CTA-equivalent designation administered by the Irish Tax Institute.
Allowance: Synonym for deduction in UK usage. The UK personal allowance (£12,570) is the income band on which no income tax is paid.
Bracket / Band: A range of income taxed at a single rate. Ireland has two bands (20 %, 40 %); the UK has four (0 % personal allowance, 20 % basic, 40 % higher, 45 % additional); US federal has seven bands.
Class 1 NI: UK National Insurance for employees. 8 % between £12,570 and £50,270; 2 % above £50,270.
CSG / CRDS: French social-charge equivalents to PRSI/USC. Together approximately 9.7 % on most labour income.
CTA: Chartered Tax Adviser. Designation administered by the Chartered Institute of Taxation (UK) and the Irish Tax Institute (Ireland).
Deduction: Reduces taxable income before bracket rates apply. Value scales with marginal rate. See the deductions page.
Domicile: A common-law concept of permanent home. Distinct from tax residence. Relevant in Ireland and the UK for the remittance basis on foreign income.
Double taxation: Being subject to tax in two jurisdictions on the same income. Mitigated by tax treaties (~3,500 bilateral treaties worldwide) and unilateral foreign tax credits.
Effective rate: Total tax divided by gross income. The average tax burden. Typically 30–55 % lower than the marginal rate for taxpayers in the top band.
Exemption: Income removed from taxable income entirely. Common examples: Irish age-related exemption, US municipal bond interest, UK ISA growth.
FICA: Federal Insurance Contributions Act. The US payroll tax: 6.2 % Social Security (capped at $168,600 in 2024) plus 1.45 % Medicare (uncapped) plus 0.9 % additional Medicare above $200k single / $250k married.
FEIE: Foreign Earned Income Exclusion. The mechanism by which US citizens abroad exclude up to $130,000 (2025) of foreign-earned income from US tax.
HMRC: HM Revenue and Customs. The UK tax authority.
IRS: Internal Revenue Service. The US federal tax authority.
Marginal rate: The rate applied to the next euro of income. The right rate to use for most planning decisions. See the marginal vs effective page.
National Insurance (NI): The UK social-insurance system, distinct from income tax. Funds State Pension and Universal Credit.
OECD Model Tax Convention: The template most modern bilateral tax treaties follow. Allocates taxing rights between residence and source countries.
PAYE: Pay As You Earn. The withholding mechanism by which employers deduct income tax and (in IE/UK) social charges from gross pay before transferring net pay to the employee.
Permanent establishment (PE): A taxable business presence in a foreign country. Triggered by various activities (fixed place of business, dependent agent). Critical concept in cross-border employment of remote workers.
Personal allowance / Personal credit: UK term (allowance) and Irish term (credit) for the income band or tax credit amount available to all standard-status individual taxpayers.
Personal Tax Credit: Irish equivalent of a personal allowance, but applied as a tax credit (€1,775 in 2025/26 for single PAYE workers) rather than a deduction.
PRSI: Pay Related Social Insurance. The Irish social-insurance contribution. 4.1 % Class A employees on income above ~€18,304/year, no upper cap.
Residence: Tax residence in a given jurisdiction. Determined by physical presence, permanent home, centre of vital interests, and other tests. Most jurisdictions tax residents on worldwide income.
Revenue Commissioners: The Irish tax authority. Often referred to simply as “Revenue.”
SARP: Special Assignee Relief Programme. Irish tax relief for foreign employees assigned to Ireland on specific terms; reduces effective tax rate by approximately 30 % on income above €100,000.
Self-Assessment: UK and Irish tax-return regime for individuals with non-PAYE income (rental, self-employment, foreign earnings, capital gains). Requires October/November filing.
Standard rate / Basic rate: The lowest non-zero income tax rate. Ireland 20 %; UK 20 % (basic); US 10 %/12 %/22 % across multiple low-bracket bands.
Tax credit: Reduces tax owed directly, after bracket rates. Value is fixed regardless of marginal rate.
USC: Universal Social Charge. Irish progressive social charge introduced in 2011: 2 %/4 %/8 % across income bands; exempt below €13,000.
Wage base: The maximum income subject to a particular social charge. US Social Security wage base: $168,600 (2024). Above the cap, no further Social Security tax is levied.