From MIM Wiki
As a foreigner residing in Poland, you are obliged to file a Polish tax return for your income until end of April of each year. Personal Income Tax (PIT) declaration needs to be filled out and either sent to the Polish Tax Authorities by post (registered mail), through an electronic system e-PIT or handed out personally at the department of your local Tax Authority.
Depending on the source of your income you would need to fill out different forms. All documents for each year are listed here. The ones of possible interest for you are:
- PIT-36 base tax form for employees,
- PIT-8C to declare the income from grants and scholarships.
By failing to file your tax return on time, the authorities may put a fine on you.