Romania-UK Tax Treaty and the 183-Day Rule: What Employers Must Track for Foreign Assignees in 2026

HR teams that send employees into Romania on assignment have a new reason to check their tax residency paperwork this year. Romania's double tax treaty with the United Kingdom, ratified by presidential decree in late October 2025, became applicable from 1 January 2026 for Romanian taxes and in stages through April 2026 on the UK side. For any employer moving UK nationals into Romanian roles, or Romanian assignees into the UK, the treaty changes which country has the first claim on tax residency when an assignment straddles both jurisdictions.

But treaty updates are the easy part to miss if the basics are not already in place. Every year, Romanian subsidiaries and EOR arrangements run into the same friction point: nobody flagged that an assignee had quietly crossed the 183-day threshold, nobody filed the ANAF questionnaire on time, and by the time payroll asks for a tax residency certificate, the employee has already missed the window to register cleanly.

This guide walks through how Romanian tax residency actually gets determined for foreign assignees, what the new UK treaty changes, and what employers need in place before, during, and after an assignment to stay compliant with ANAF.

The Romania-UK Treaty Change and Who It Affects

The new Romania-UK Income Tax Treaty, ratified in Romania via Law No. 169/2025 and a presidential decree issued on 29 October 2025, replaces the earlier UK-Romania double taxation arrangement. It applies in Romania from 1 January 2026, while the UK side phases it in across withholding tax, corporation tax, and income and capital gains tax between January and April 2026.

For global mobility teams, the practical effect is on the tie-breaker tests used when an assignee could be considered tax resident in both countries. Where an employee retains a home, family, or economic ties in the UK but spends extended periods working in Romania, the treaty's residency tie-breaker sequence, rather than Romanian domestic law alone, now determines which state has primary taxing rights under this updated agreement. Employers with UK-Romania assignment corridors should have payroll and tax advisors confirm which version of the treaty applies to any assignment that spans the transition period, since an assignment that started under the old treaty and continues into 2026 may need a fresh residency assessment.

How the 183-Day Rule Actually Works

Romanian domestic law sets out several independent tests for tax residency, and the 183-day rule is only one of them. An individual becomes a Romanian tax resident, triggering full taxation on worldwide income rather than just Romanian-source income, if any of the following apply:

• Physical presence in Romania exceeding 183 days in any 12-month period
• A home available in Romania to the individual or their family
• Romania being the location of the person's centre of vital interests (where personal and economic ties are strongest)
• Romanian domicile, for Romanian citizens

The 183-day count is not a calendar-year count. ANAF tracks presence across any rolling 12-month window, which means an assignee who splits time across two calendar years can still cross the threshold mid-assignment without realizing it. This is the single most common compliance gap employers run into: nobody is tracking the rolling count against entry and exit dates in real time.

The ANAF Residency Questionnaires and Certificate Process

Romania does not leave residency status to informal interpretation. ANAF requires foreign individuals to file a formal questionnaire when they arrive to work in Romania and another when they leave, so the tax authority can issue a determination rather than relying on self-assessment.

• On arrival, the assignee files the questionnaire for establishing fiscal residence, generally due once it becomes clear the 183-day threshold will be reached, together with a passport copy, proof of accommodation, and any foreign tax residency documentation.
• On departure, a separate questionnaire is filed in advance of leaving Romania, so ANAF can close out the individual's resident status and confirm the date from which only Romanian-source income remains taxable, if any.
• ANAF reviews the submission and supporting documents and issues a notice confirming the individual's residency status and associated filing obligations.
• A tax residency certificate, the document assignees need to claim treaty benefits or prove Romanian residency to a home-country tax authority, is requested separately once residency status is established, and is typically needed annually to support treaty relief claims.

Employers who run this process reactively, only once an assignee or a foreign tax authority asks for a certificate, tend to find the underlying questionnaire was filed late or not at all, which delays the certificate and can expose the assignee to double taxation in the interim.

SPV Registration and the NIF for Foreign Assignees

Foreign individuals without a Romanian CNP (personal numerical code) need a NIF, a tax identification number, before ANAF can process any residency filing, payroll registration, or tax return in their name. The NIF is obtained through Form 030, filed with supporting identity documents, proof of the Romanian fiscal reason triggering registration, such as Romanian-source employment income, and certified translations where required. Getting a NIF does not by itself make someone tax resident; it simply gives ANAF a file reference to attach subsequent filings to.

Once registered, individuals interact with ANAF primarily through the Spatiul Privat Virtual (SPV) online portal, which has become the mandatory channel for most tax correspondence, filings, and e-invoicing interactions. Individual enrolment is done either through a video identification session with an ANAF inspector, which must be completed within a set window after the request is submitted, or, for people who already hold a prior ANAF registration number, through a faster document-based verification. Employers managing multiple assignees should budget time for the video identification step specifically, since scheduling it is often the rate-limiting factor in getting a new assignee fully set up with ANAF.

Practical Steps for Employers Before an Assignment Starts

Getting ahead of residency determination is simpler than fixing a late filing. Before an assignee's start date, employers should:

• Confirm the assignment's expected duration and whether it is likely to cross 183 days within any 12-month window
• Flag whether a relevant double tax treaty, including the updated Romania-UK agreement where applicable, affects which country holds primary taxing rights
• Begin the NIF registration process early if the assignee has no Romanian CNP
• Set a calendar reminder tied to the rolling 183-day count, not the calendar year, so the ANAF arrival questionnaire is filed on time
• Plan for the tax residency certificate request as a recurring annual task for the duration of the assignment, not a one-off

How Nestlers Group Supports Tax Residency Compliance for Assignees

Nestlers Group's Tax Services team manages the practical side of residency compliance for employers bringing foreign assignees into Romania, including tax residency certificate applications, tax registration for foreign citizens through the NIF process, SPV account setup and enrolment, and the monthly tax liability calculations that follow once an assignee's residency status is confirmed. For assignments structured as postings rather than direct local employment, the team also handles the tax assessment on posting contracts, which determines how home-country and Romanian tax obligations interact for the duration of the posting.

For employers running assignments through an Employer of Record arrangement, Nestlers Group's EOR service keeps residency tracking, payroll, and ANAF filings aligned under one point of contact, which matters most for exactly the kind of rolling 183-day monitoring that otherwise falls through the cracks between HR, payroll, and the assignee themselves. Clients who want a broader compliance review before an assignment begins can also engage the Global Mobility end-to-end management service, which incorporates residency planning into the overall relocation and assignment timeline rather than treating it as a separate afterthought.

Sources: ANAF, Guidelines for Fiscal Residence of Individuals (2025 edition); EY Romania, Tax Alert on Fiscal Code Amendments and Romania-UK Double Taxation Convention (January 2026); KPMG, Romania Tax Treaties with Andorra and UK Ratified (December 2025); UK Government, UK/Romania Double Taxation Convention, Treaty Series No. 23/2026; TheRomanianLawyers, NIF Code in Romania guide (2026); CreativDigital, ANAF SPV Registration Guide (2026).