Days, Months and Seasons in Pali

Pāḷivāramāsa-utū
Days, Months and Seasons in Pāḷi
(Abhidhānappadīpaka, v. 74-81)

Ghaṭikā saṭṭhyahoratto, pakkho te dasapañca ca,
There are sixty hours in the day and night, a fortnight has fifteen of these (days), Sometimes a fortnight has only 14, see below for deatils.

Te tu pubbāparā sukkakāḷā, māso tu te duve.
There are the former and later, brightening and darkening (fortnights), and there are two of these to a month.

Citto, Vesākha, Jeṭṭho c' Āsāḷho dvīsu ca Sāvaṇo,
Citta, Vesākha, Jeṭṭha and Āsāḷha, and the two Sāvaṇa. There are potentially two of these months as there is an occasional need to adjust the moon calendar to the sun calendar. These days that adjustment is made at the end of the Hot Season. It is known as the adhikamāsa or, extra month.

Poṭṭhapād' Assayujā ca māsā dvādasa Kattiko.The month is normally written in the feminine gender, as Kattikā, but in Abhidhānappadīpaka it is given as a masculine.
Poṭṭhapāda, Assayuja, the twelve months (include) Kattika.

Māgasiro tathā Phusso, kamena Māgha-Phagguṇā.
Māgasira and then Phussa, and by and by Māgha (and) Phagguṇa.

Kattik' Assayujā māsā pacchimapubba-Kattikā.
The months Kattika and Assayuja are (also) known as the late and early Kattika.

Sāvaṇo Nikkhamanīyo, Cittamāso tu Rammako. These are alternative names.
Sāvaṇa (is also known as) Nikkhamanīya, the month Citta (is also known as) Rammaka.

Caturo caturo māsā, Kattikakāḷapakkhato
Four by four months, (starting) from the darkening fortnight in Kattika

Kamā Hemanta-Gimhāna-Vassānā utuyo dvisu.
In order there is the Winter, Summer and Rainy seasons (divided) in two.

Hemanto Sisiram-utū, cha vā Vasanto ca Gimha-Vassānā,
The six seasons are: Snowy (and) Cool, Spring (and) Hot, Rainy

Sarado ti kamā māsā, dve dve vuttānusārena.
(And) Autumn, that is the order of the months, two by two according to what is said.

Uṇho nidāgho gimho 'tha, vasso Vassānapāvusā,
Then there is the Hot, the Boiling (or) the Heat (season), the Rains, the Rainy (or) the Showery (season), These are alternative names.

Utūhi tīhi Vassānādikehi dakkhiṇāyanaṁ,
In the three seasons, from the beginning of the Rainy (season, the Sun) goes by the southern path,

Uttarāyanam-aññehi, tīhi vassāyanadvayaṁ.
(It goes) by the northerly path in the other (months), in the year there are (these) two paths.

(In the English column the less likely month is written in small text, and the more likely month is in normal script.)

In the Buddhist system the half-month itself normally consists of either 15 days (normally 18 times a year) or 14 days (normally 6 times a year). The month starts the day after the new moon, running up till the following new moon. The season begins though the day after the full moon.

The Buddhist calendar calculations are based on the Lunisolar year. Important dates (like the Awakening) being commemorated on the moon cycle, and the moon cycle itself being adjusted to fit in with the solar cycle.

As can be seen from the diagram below this results in there being 6 months with 30 days and 6 with 29 days, making a total for the year of 354 days, which is 11 days short of the rounded up figure of 365 days for the solar year. To bring the moon cycle back into line with the solar cycle we need to add in an extra month (adhikamāsa) to the calendar usually every 3 years, and occasionally every 2 years (it normally needs 7 extra months every 19 years). The extra month is added in before Āsāḷha, and is called Adhika Āsālḥa (extra Āsāḷha, in Thailand it is called the second Āsāḷha).

Intercalary days (adhikavāra) are also added in, as and when required, there being 11 extra days every 57 years. This is done by adding an extra day to the 14^th day uposatha in Jeṭṭha, and does not normally happen in a year when the extra month (adhikamāsa) in being added in.

The Buddhist era (BE, which begins at year 0 in Sri Lanka, and year 1 in Thailand) starts at the day the Buddha attained Parinibbāna, which, according to the traditional reckoning was on 11th March 544 BC (this date is disputed by many scholars, but this is the date that is current in Buddhist countries). According to this dating he was therefore born in 624 BC and attained Awakening in 589 BC.

The days of the week do not seem to be mentioned in Pāḷi literature
but they are given in Ven. Buddhadatta’s English-Pali Dictionary as follows:

Candavāra = Monday
Kujavāra = Tuesday
Budhavāra = Wednesday
Guruvāra = Thursday
Sukkavāra = Friday
Sanivāra = Saturday
Ravivāra = Sunday

Note that the new day begins at dawn, and this is calculted as being roughly 1/2 hr before sunrise.