The first day of Diwali, kept in the evening.
Dhanteras is Kartika Krishna Trayodashi — the Trayodashi of the krishna fortnight of Kartika. It is kept after sunset, so the date is the day that tithi is running pradosh, the hour and a half following sunset.
Computed from the Moon’s elongation with the Swiss Ephemeris, sidereal, Lahiri ayanamsa. A tithi begins and ends at a real minute rather than at midnight, which is why the moment above decides the day — and why the same tithi read at a different hour can name a different date.
Cast a free kundli, or ask any of 24 astrologers what this year actually holds for you. Billed by the minute, and only while somebody is answering.