The Hindu calendar is based on lunar months corresponding to the phases of the moon. In one year there are twelve months of 29.5 days, accounting for a total of 354 days.The shortfall means that the date of each festival moves back 11 days each year. To rectify this, an extra leap month is added about once every three years. The Hindu calendar is therefore luni-solar, with a precise month and an approximate year.
The year – starting with Makara Sankranti, the sun's entrance into Capricorn
– is divided into two halves and six seasons. There are various ways of reckoning
the New Year; most common is the day after the new moon in the month of Chaitra
or, in Gujarat, the day after the Diwali new moon. Various eras are used for
numbering the years; the most common are the Vikrami Era, beginning with the
coronation of King Vikram-aditya in 57 BCE and the Shaka Era, counting from
78 CE. In rituals the priest often announces the dates according to KaliYuga,
(see Kala: Time). For these three systems,
the year 2000 corresponds to 2057, 1922, and 5102 respectively, though the
last figure is subject to some debate.
Above: The diagram shows the Hindu year, with months and the corresponding
festivals. It is somewhat approximate, as the exact dates change yearly
relative to the Gregorian calendar – with a month between the earliest and
latest possible dates. A few festivals are determined by the sun alone,
and their Gregorian dates are the same (or within one day) each year.
Within each month, there are two "fortnights," each consisting of 15 "lunar days." Although the solar and lunar days technically begin at different times, each solar day is ascribed one particular lunar day numbered from one to fifteen, either of the bright fortnight (waxing moon) or the dark fortnight (waning moon). Months average out to 29.5 days, so occasionally a day will be dropped. For example, in one month, the fourth day of the waxing moon may be followed by the sixth.
There are two main calendars. In North India, the month generally begins with the full moon, in South India with the new moon. Festival days will still fall on the same day, or very closely, but the name of the month may be different. For example, Krishna's Birthday falls on the eighth day of the dark moon; in the North this is in the month of Bhadra; in the South in Shravana.
The week is divided into seven days, each corresponding to one of seven planets, exactly as in the West. No day is particularly special but each is related to a specific deity. For example, Monday is often associated with Shiva and Tuesday with Hanuman. Hindus may perform fasts and recite prayers to supplicate a particular deity on the corresponding day of the week.
The day usually begins at dawn, or just before, according to which astronomical and astrological systems are used. The day is divided into 15 muhurtas, each of about 48 minutes, and the night is similarly divided. Traditionally brahmanas chant the Gayatri mantra at sunrise, noon and sunset because these are considered particularly important times of the day. The first two muhurtas (about one hour) of the morning before dawn are considered most auspicious, especially for spiritual practices.