How the dates are counted

The day begins at sunrise

In the panjika a day’s tithi is the one running at the moment of sunrise. The Bengali date changes at sunrise too, not at midnight. So even when the tithi ends in the morning, the day keeps the sunrise tithi.

Every time on this website is for Kolkata, in Indian Standard Time. The app uses the sunrise of the city you choose.

What a tithi is

A tithi is complete each time the Moon gains another 12 degrees on the Sun; thirty tithis make a lunar month, new moon to new moon. The Moon’s speed varies, so a tithi lasts roughly 20 to 27 hours. Some tithis span two sunrises, and some touch none: a kshaya tithi.

When a Bengali month begins

In West Bengal a Bengali month begins from the Sun’s sankranti, the moment it enters the next sign: if that moment falls between sunrise and midnight, the next day is the 1st; if after midnight, the day after that. So months run 29 to 32 days.

Bangladesh uses a different, fixed calendar: 1 Boishakh is always 14 April and month lengths are set. So the two countries’ Bengali dates are often two or three days apart.

How a festival’s day is chosen

Each puja has its tithi, and the day goes by when in the day that tithi holds: at sunrise for some, in the forenoon, at midday or in the afternoon for others, in the evening (pradosha) or at midnight (nishitha) for others again. Kali Puja is on the night whose midnight holds the Amavasya; Saraswati Puja on the day whose forenoon holds the Panchami. When the tithi spans two days, a rule says which, most of them from Raghunandana’s Tithitattva.

Each festival’s page gives its rule in full, and says so when another source’s rule gives another day.

Two schools of panjika

West Bengal’s panjikas follow two schools. The traditional Surya Siddhanta school: the Gupta Press Directory Panjika, Beni Madhab Sil’s panjika, Madan Gupta’s panjika. The Drik school, the modern calculation of the Sun and Moon: the Bisuddha Siddhanta panjika. Their tithi times can differ by hours, so in some years a puja’s day differs too.

The app and this website both count by the Drik school for now. The traditional school is built but still to be checked against a full printed year, so the app does not offer it yet, and wherever this website shows it, it is labelled ‘unverified calculation’.

Checked against print

448/456Of 456 puja and festival days and Sandhi Puja times printed under the name of a Drik-school panjika, 448 match Ritupatra’s calculation. 2017 and 2020 to 2027, Kolkata.

The sources: the Bisuddha Siddhanta panjika as quoted in the news, the printed lists of Belur Math and Ramakrishna Math Kamarpukur, drikpanchang.com, and the Government of India’s Rashtriya Panchang (IMD). Each claim is kept with its source’s address and its exact words.

The tithi times are checked too: across 45 days of the Drik panjika printed in Bartaman, the tithi at sunrise matches 45 of 45, and every tithi’s end falls within 2 minutes.

What is still to be checked

• The traditional school is fitted to seven weeks of printed dates, not to a whole year. The full year will be checked against the printed 1434 panjika.
• The Drik school is checked against times printed in the news, not yet against the printed Bisuddha Siddhanta panjika. On a day whose tithi changes within about 4 minutes of sunrise, the day’s tithi depends on how sunrise is defined.
• Mahalaya 2027: by the afternoon rule Ritupatra’s day is Wednesday, 29 September 2027; two articles count by sunrise and give 30 September. The 1434 panjikas will settle it.

The Sun and the Moon

The positions of the Sun and Moon, sunrise and sunset are computed by the methods of Astronomy Engine (free software, MIT licence), which places the Moon to within a few arcseconds. For the Drik school the signs are counted with the Lahiri ayanamsha, as the West Bengal panjikas do.