The Tax Office Requires an Income Certificate from Ukraine: How to Avoid Double Taxation
A request for an income certificate from Ukraine is not a reason to pay double tax—on the contrary, it is a way to avoid it. The tax office needs to see the full picture of income in order to correctly apply the convention between Poland and Ukraine and credit tax already paid in Ukraine.
International Law Firm "Zahist" assists clients with tax matters in Poland. In our practice, double taxation most often arises not because of the certificate request itself, but because a person ignores the letter from the tax office or fails to gather documents from Ukraine in time—and tax is assessed without regard to amounts already paid there.
We explain why this request arises, how the double tax avoidance convention works, and which documents are actually needed.
Why the Tax Office Asks for an Income Certificate from Ukraine
The Tax Office (Urząd Skarbowy) requests an income certificate from Ukraine when there are grounds to believe that a person has become a Polish tax resident but continues to receive income from Ukrainian sources as well.
Without this data, the authority simply cannot calculate tax correctly or apply the credit mechanism—so the document request works in the taxpayer’s favor, not against them.
In practice, such a letter is often perceived as a threat, although in essence it is a technical request: the official needs figures to apply the convention correctly, not an intention to assess extra tax beyond what is due.
Tax residency in Poland — the 183-day rule
Tax residency in Poland is determined primarily by the period of stay: if a person spends more than 183 days in the country during a calendar year, they generally become a Polish tax resident.
A second, less obvious criterion is the center of vital interests: where the family, main home, and work are. Residency assessment is always individual and is not limited to counting days alone.
Declaration of the center of vital interests — what it is and why it matters
A Ukrainian national may confirm the transfer of their center of interests to Poland by their own declaration (oświadczenie)—on that basis the employer immediately treats the person as a Polish resident from the first day of stay.
The employer is not obliged to verify the truthfulness of this declaration if there are no documents or information contradicting it—but the declarant remains responsible for the accuracy of the information provided.
If it later turns out that the declaration did not reflect reality—for example, the family and actual home remained in Ukraine—residency may be reviewed retroactively, and that is when the risk of additional assessments arises.
Poland–Ukraine Double Tax Avoidance Convention
The double tax avoidance convention between Poland and Ukraine exists precisely so that the same income is not taxed twice—both in the source country and in the country of residence.
For employment income, the convention exempts a non-resident from taxation in Poland only if their stay there does not exceed 183 days in a calendar year.
If that period is exceeded, employment income in Poland is taxed under Polish rules from the first day of stay.
How the proportional credit method works
When the same income could be taxed in both countries, the convention provides a credit mechanism: tax paid in Ukraine is deducted from the amount due in Poland on that same income.
It is precisely for calculating this credit that the tax office needs a certificate of income and tax paid in Ukraine—without it there is simply no basis to apply the method, and the full tax would have to be paid in Poland.
An important nuance: the credit does not always cover the entire amount—if the tax rate in Ukraine is lower than in Poland, the difference still has to be paid in Poland, not in Ukraine.
Which documents confirm income and residency in Ukraine
An income certificate is not the only document that may be required; the full package depends on the source of income and the type of employment in Poland.
- Income certificate from the Ukrainian source for the relevant period
- Tax residency certificate issued by the Ukrainian tax authority
- Documents confirming tax paid in Ukraine on the income
- Declaration of the center of vital interests (oświadczenie), if one was filed
In practice, obtaining a tax residency certificate from Ukraine can be difficult—this is often why the tax office case is delayed, and the taxpayer should start this process in advance, not only after receiving a demand letter.
If some documents objectively cannot be obtained in time due to circumstances in Ukraine, it is advisable to notify the tax office in writing and request an extension of the deadline.
Silence and a complete lack of response are always viewed worse than a partial reply explaining the reasons for the delay.
PIT-ZG and declaring foreign income in Poland
A Polish tax resident declares all of their income, including income earned abroad—for this purpose, PIT-ZG is attached to the main PIT return—information on income from foreign sources.
The form is filed separately for each country from which income was received, so for income from Ukraine a separate PIT-ZG annex is completed regardless of other foreign sources.
Omitting this annex does not exempt one from tax—on the contrary, it only makes it harder to prove the right to credit tax already paid in Ukraine when the matter is eventually reviewed.
| Situation | What to file |
| Polish resident with income only in Poland | Standard PIT return |
| Polish resident with income also in Ukraine | PIT + PIT-ZG annex for Ukraine |
| Non-resident working under a contract of mandate without a certificate | Risk of 20% flat-rate (ryczałt) withholding in Poland |
| Non-resident with a Ukrainian tax residency certificate | Taxation under the convention terms |
Common mistakes that lead to double taxation
Most cases of double taxation are not a consequence of the convention itself, but the result of several common taxpayer mistakes.
- Ignoring a tax office letter requesting a certificate—the case is decided without regard to tax paid in Ukraine
- Lack of a tax residency certificate when working under a contract of mandate
- Late filing of the declaration of the center of vital interests
- Confusion between resident status and Ukrainian citizenship
In our experience, inaction is the most costly: while documents are being collected from Ukraine, the tax office response deadlines do not stop, and without a formal request for an extension the case may be decided against the taxpayer.
Another common situation is a person simultaneously considering themselves a resident of both Ukraine and Poland, although under the convention residency is always determined in favor of only one country under clear criteria, not at the taxpayer’s arbitrary choice.
Legal assistance with tax matters in Poland
Issues of residency, application of the convention, and gathering documents from Ukraine should be considered together—separately, each of these points rarely gives the full picture.
Lawyers at International Law Firm "Zahist" help determine tax residency, prepare a response to a tax office request, and gather the documents needed to credit tax paid in Ukraine.
If you have received a letter demanding an income certificate from Ukraine and are unsure how to proceed, contact International Law Firm "Zahist"—we will review your situation at a consultation.
