The Mahalaya Paksha rituals are held during the dark fortnight of Ashwayuja (September-October). This period is sacred for doing rituals and offering oblations to the souls of the departed ancestors. The last day of Mahalaya Paksha or Pitr Paksh is the most important day in a year to perform rites to departed souls. In 2007, Mahalaya Paksha is from September 27 to October 11. The Shradh Tarpan is on October 10 and Amawasya Shradh or the Mahalya is on October 11. In some calendars, especially Bengali, the Mahalaya is on October 10.
Note: The Mahalaya Associated with Durga Puja is on October 10 according to Bengali Calendars.
Starting from September 27 the 14 Shradh dates are Prtipada Shradh, Dwitiya Shradh (Sept 28), Tritiya Shradh (Sept 29), Chaturthi Shradh/Pancahmi Shradh (Sept 39), Shashti Shradh (October 1), Saptmi Shradh (Oct 2), Ashtmi Shradh (Oct 3), Navmi Shradh (Oct 4), Dashmi Shradh (Oct 5), Ekadshi Shradh (Oct 6), Dwadshi Shradh (Oct 7), Triodshi Shradh (Oct 8), Chaturdashi Shradh (Oct 9), Shradh Tarpan (Oct 10) and Amawasya Shradh (Oct 11)
The main offering during the Mahalya Paksha to ancestors is food. It is believed that the offering made during this period will benefit all the departed souls.
Charity in the form of food is also done by people. Some people avoid non-vegetarian food and abstain from alcohol and avoid sexual contact.
More details about Mahalaya Paksha can be found in the article on Pitr Paksh.