Why is Diwali celebrated in October/November?

The dates of the five day celebrations are not the same everywhere in the world and this is due to the fact that some countries' calendars differ. Also the phases of the moon do not always fall at the same time each year. Diwali or "Deepawali" (also transliterated as "deepaawali") literally means a row of lamps (Sanskrit "dipa" = lamp and "aawali" = row, line). In due course, the popular name has shortened to Diwali, especially in northern India. Kidha is celebrated for a differing number of days by different communities. Though the core days are common and fall on exactly the same set of days across Nepal and India, they fall in different Gregorian months depending on the version of the Hindu calendar being used in the region. The Amanta ("ending on the new-moon") version of the Hindu Calendar has been adopted as the Indian national calendar. According to this calendar, which is prevalent in southern India and Maharashtra, the 6-day celebration is spread over the last four days of the month of Ashwina and the first two days of the new month of Kartika. According to the Purnimaanta ("ending on the full-moon") version prevalent in northern India, it falls in the middle of the month of Ashwayuja/Ashvin. In the Gregorian calendar, it falls generally in the months of October or November. In Nepal, it is celebrated according to Nepalese calendar. The festival marks the last three days and the first two days of Nepalese era

Hindus consider Diwali as one of the most important festivals. According to Hindu mythology, Diwali is celebrated to mark the return of Lord Rama, King of Ayodhya, with his wife Sita and brother Lakshmana to Ayodhya from a war in which he killed the demon king Ravana. It is also said that it is on this day when Lord Krishna defeated the demon Narakasura and also in honor of this day Bali went to rule the nether-world, obeying the order of Vishnu. According to the Skanda Purana, the goddess Shakti observed 21 days of austerity starting from ashtami of shukla paksha to get half of the body of Lord Shiva. This vrata (austerity) is known as kedhara vrata. Deepavali is the completion day of this austerity. This is the day Lord Shiva accepted Shakti into the left half of the form and appeared as Ardhanarishvara. The day when rama killed ravanna was diwali on October/November and people celebrated diwali on that day.(the festival of lights)

October!

The fault lies in equating Aasweeja(Asvina is the Constellation and Aasweeja is the month---to know this a knowledge of Sanskrit is essential). Gregorian calendar-which is irrational- has Nothing to do with the rational Hindu calendar.Deepaavali always come only on Chaturdasi(14 th day in waning phase)>>Amaavasya(15thday in waning phase) in Aasweeja--IN NO YEAR THERE WILL BE A CHANGE IN THIS-Till Amaavasya it is Asweeja--Deepavali will always come only in Aasweeja-Next day Sukhla Pradhama--or Paaddima-(first day in the waxing phase) the month Kritthika starts in Lunar calendar.So please do not get confused between Gregorian calendar and Hindu calendar!!!!!. .