Pitru Paksha is a 15 lunar day’s period when Hindus pay homage to their ancestors, especially through food offerings.
According to South Indian Amavasyant calendar it falls in the lunar month of Bhadrapada beginning with the full moon day or day after full moon day.
According to North Indian Purnimant calendar this period falls in the lunar month of Ashwin beginning with the full moon day in Bhadrapada or next day of full moon day.
It is just nomenclature of lunar months which differs and both North Indians and South Indians perform Shraddha ritual on similar days.
20 September (Monday) Purnima Shraddha
21 September (Tuesday) Pratipada Shraddha
22 September (Wednesday) Dwitiya Shraddha
23 September (Thursday) Tritiya Shraddha
24 September (Friday) Maha Bharani, Chaturthi Shraddha
25 September (Saturday) Panchami Shraddha
26 September (Sunday) Shashthi Shraddha
28 September (Tuesday) Saptami Shraddha
29 September (Wednesday) Ashtami Shraddha
30 September (Thursday) Navami Shraddha
01 October (Friday) Dashami Shraddha
02 October (Saturday) Ekadashi Shraddha
03 October (Sunday) Magha Shraddha, Dwadashi Shraddha
04 October (Monday) Trayodashi Shraddha
05 October (Tuesday) Chaturdashi Shraddha
06 October (Wednesday) Sarva Pitru Amavasya