Polish Tax Residency and Working in Denmark: 2026 Guide

For thousands of Polish workers crossing into Denmark every year, the question of Polish tax residency and work in Denmark is anything but academic. Many assume that once they start earning a Danish salary, their obligations to the Polish tax office simply disappear. That assumption can be costly. Under Polish law, a person who maintains their centre of personal or economic interests in Poland remains a Polish tax resident, regardless of where their employer is registered or where the payslips come from. Understanding exactly when Polish PIT applies is the first practical step toward avoiding double taxation, penalties, and sleepless nights before April.

Step 1: Determine Whether You Are a Polish Tax Resident

Polish tax residency is governed by the Ustawa o podatku dochodowym od osób fizycznych (the Personal Income Tax Act). The law sets out two independent tests. First, the physical presence test: if you spend more than 183 days in a calendar year on Polish territory, you are automatically considered a Polish resident for that year. Second, and often overlooked, the centre-of-vital-interests test: if your spouse, children, or primary home remain in Poland, Polish authorities may treat you as a resident even when you spend the majority of your working days in Denmark.

The practical consequence is unlimited tax liability in Poland, meaning your worldwide income, including your Danish wages, falls within the scope of Polish PIT. The Polish tax authority, Krajowa Administracja Skarbowa, administers these rules and publishes guidance on residency determination that every worker should consult before the tax year closes.

To illustrate with a hypothetical example: imagine a construction worker who leaves for Denmark in January, works there for nine months on a posted-worker contract, but whose wife and two children continue living in Warsaw. Even though he spent fewer than 183 days in Poland that year, his centre of vital interests remained there. Under the Personal Income Tax Act, he would still be treated as a Polish resident and required to declare his Danish income in Poland, subject to the relief mechanisms of the double taxation treaty.

Step 2: Gather the Required Documents

Before you can correctly file your Polish PIT return, you need a clear paper trail. The essential documents include your Danish annual tax statement (known as an årsopgørelse), issued automatically by Skattestyrelsen, the Danish tax authority. You will also need proof of the number of days spent in each country, your employment contract or posted-worker assignment letter, and, if applicable, your A1 certificate confirming which country's social security system you contribute to.

The A1 certificate matters here because social insurance and income tax follow different rules. A worker posted from Poland under the rules of EU Regulation 883/2004 may continue paying ZUS contributions in Poland while simultaneously owing income tax in Denmark or Poland depending on the residency analysis. Keeping these two tracks separate avoids one of the most common errors workers make when dealing with cross-border employment. For context on the contractual documentation side, the article on Penalty for No Written Contract with Posted Worker in Denmark 2026 explains what Danish law requires from employers, which in turn shapes the documents available to workers at tax time.

Step 3: Understand the Poland-Denmark Double Taxation Treaty

Poland and Denmark have a bilateral agreement to prevent double taxation. Under this treaty, employment income is generally taxable in the country where the work is physically performed. This means that if you genuinely work in Denmark, Denmark has the primary right to tax those wages. Poland then applies the exemption with progression method or the credit method, depending on the type of income, to ensure you are not taxed twice on the same earnings.

The exemption with progression method means your Danish income is exempt from Polish PIT but is still counted when calculating the effective tax rate applied to any remaining Polish-source income you may have, such as rental income from a flat in Kraków or interest from a Polish bank account. This is a nuance that catches many workers off guard during their first year of cross-border employment.

Step 4: Fill Out the Correct Polish Tax Forms

Polish residents with foreign income typically file a PIT-36 return rather than the simpler PIT-37. The PIT-36 includes a dedicated section for foreign income and allows you to apply the double taxation treaty relief. The Polish e-Tax portal, available at podatki.gov.pl, offers a guided online filing tool that pre-populates some data and walks you through each section. The deadline for filing PIT-36 is April 30 of the year following the tax year in question.

Attach your Danish årsopgørelse as supporting documentation. If the portal does not accept foreign-language attachments directly, prepare a simple translation of the key figures: gross income, tax withheld in Denmark, and the period covered. Tax offices across Poland have become increasingly familiar with Danish tax documents, but a clear summary saves time if your return is selected for review.

Step 5: Submit and Track Your Return

Once submitted electronically through the e-Tax portal, you will receive an official reference number. Keep this number along with a PDF copy of the submitted return. Processing times vary, but straightforward returns with foreign income are typically resolved within a few months. If the tax office requires additional clarification, they will contact you in writing, so ensure your registered address in Poland is current.

Workers who manage their cross-border paperwork digitally will find that having all documents in one organised system, rather than scattered across email threads and spreadsheets, dramatically reduces errors. The transition to structured digital tools is something the article on How to Switch from Messenger and Excel to Agency Software 2026 addresses in detail for agencies and workers alike.

Common Mistakes to Avoid

The most frequent mistake is assuming that paying tax in Denmark automatically ends any Polish obligation. It does not, as long as Polish residency persists. A second common error is failing to file a PIT-36 at all on the grounds that "Denmark already taxed everything." Even if no additional Polish tax is due after applying treaty relief, the filing obligation itself remains if you are a Polish resident with foreign income.

Another pitfall involves the A1 certificate and ZUS. Some workers stop paying Polish social contributions when they start working in Denmark without obtaining an A1 certificate first, creating gaps in their Polish pension and health insurance record. The ZUS website provides detailed guidance on the A1 application process and the conditions under which Polish social security coverage continues during a posting abroad.

Finally, workers employed through Danish construction sites should be aware that their Danish employer or client may be subject to Danish registration and reporting obligations. The rules around digital safety documentation and site compliance are covered in the guide to SSL Certificate and Safety Card on Danish Sites: 2026 Guide, which is relevant context for understanding the broader compliance environment you operate in.

Practical Advice Before You File

Start by requesting your Danish årsopgørelse from Skattestyrelsen as soon as it becomes available, typically in March. Cross-reference the Danish income figures with your own payslips to catch any discrepancies early. If your family situation, days spent in Poland, or income sources changed significantly during the year, consider consulting a tax adviser who specialises in Polish-Danish cross-border cases before filing. The cost of professional advice is almost always lower than the cost of a correction, a late-filing penalty, or an audit that drags on for months. Acting early, keeping documents organised, and understanding that Polish tax residency does not disappear the moment you board a flight to Copenhagen are the three habits that separate workers who handle this smoothly from those who do not.