The Hindu Calendar (Panchang)

Hindus use traditional calendars to fix the dates of festivals, fasts, ceremonies and auspicious times. Unlike the Western (Gregorian) calendar, which follows the sun alone, most Hindu calendars are lunisolar: months follow the phases of the moon, while the year as a whole is kept in step with the sun and the seasons. This is why Hindu festivals fall on different Western dates each year. See The Hindu festival year.

Months and fortnights

A lunar month lasts about 29.5 days, from one new moon to the next. It is divided into two fortnights (paksha):

• Shukla paksha, the bright fortnight, as the moon waxes from new to full.
• Krishna paksha, the dark fortnight, as the moon wanes from full to new.

The twelve months are: Chaitra, Vaishakha, Jyeshtha, Ashadha, Shravana, Bhadrapada, Ashvin, Kartika, Margashirsha, Pausha, Magha and Phalguna. Chaitra usually begins in March or April.

In north India, months usually end at the full moon (the purnimanta system), while in much of south and west India they end at the new moon (the amanta system). This means the same festival can be described as falling in different months in different regions, even when it is celebrated on the same day.

Tithis: lunar days

Each lunar month contains thirty lunar days, called tithis, fifteen in each fortnight. A tithi is the time it takes for the angle between the moon and the sun to grow by 12 degrees. Tithis vary in length and do not match solar days exactly, so a tithi may begin in the middle of a day, and occasionally a tithi is skipped or repeated. Festivals are fixed by tithi: for example, Janmashtami falls on the eighth tithi (ashtami) of the dark fortnight of Bhadrapada.

Keeping in step with the sun

Twelve lunar months make about 354 days, eleven days shorter than the solar year. To prevent the months drifting through the seasons, an extra month, called adhika masa (“added month”), is inserted roughly every two and a half to three years. Major festivals are not held in the adhika masa, which is regarded as especially suitable for devotion and charity.

Some regional calendars, such as those of Tamil Nadu, Kerala, Bengal and Odisha, are based on solar months, named after the sun's entry into each zodiac sign.

Eras

• Vikram Samvat, widely used in north and west India and the official calendar of Nepal, is counted from 57 BCE. Its years are about 57 years ahead of the Western calendar.
• Shaka Samvat, counted from 78 CE, is the basis of India's official National Calendar, adopted in 1957.

The Hindu New Year is celebrated at different times in different regions: in Chaitra (March–April) as Ugadi or Gudi Padwa, in mid-April as the solar new year, or, in Gujarat, on the day after Diwali.

The panchang

A Hindu almanac is called a panchang, meaning “five limbs”, because it records five elements for each day:

1. Tithi: the lunar day.
2. Vara: the day of the week.
3. Nakshatra: which of the 27 lunar constellations the moon is in.
4. Yoga: a combination of the positions of sun and moon.
5. Karana: half a tithi.

Priests and families use the panchang to choose auspicious times (muhurta) for weddings, house-warmings, journeys and other events, and to avoid inauspicious periods such as Rahu kalam. Panchangs are now widely available as printed calendars, websites and phone apps, and many British mandirs publish their own each year.

The days of the week

The Hindu days of the week are named after the sun, moon and planets, like their Western equivalents: Ravivar (Sunday, the sun), Somvar (Monday, the moon), Mangalvar (Tuesday, Mars), Budhvar (Wednesday, Mercury), Guruvar (Thursday, Jupiter), Shukravar (Friday, Venus) and Shanivar (Saturday, Saturn).

Sources and further reading

• Robert Sewell and Sankara Balkrishna Dikshit, The Indian Calendar (1896).
• Kim Plofker, Mathematics in India (Princeton University Press, 2009).