Answer

If you mean Sthanakvasi Paryushan, it is observed for 8 days and generally begins on Bhadarva Vad 12 and ends on Bhadarva Vad 4 in the Jain calendar.

The last day is celebrated as Samvatsari, the most important day of forgiveness.

Note

The exact English calendar dates change every year. Please tell me which year you are asking about, and I can help explain the Paryushan dates for that year.