Each year between February and April 30th, all employees who have worked in Poland in the previous year, have to submit their annual Personal Income Tax declarations (PIT) to the fiscal authorities. Currently, it’s time to submit your PIT for the year 2020.
There are various PIT forms marked with different numbers but the most common form is PIT-37 for employees who do not run their own business and did not have any income from other countries in 2020.
More informaction on source page:
https://www.euraxess.pl/poland/news/submit-your-annual-tax-declaration-pit