Strictly speaking, there is no single Hindu calendar. India is a very diverse country, and this diversity is also reflected in the Hindu calendar. Different regions of India follow their own calendars. However, all these calendars have certain common attributes. For example, almost of the calendars are lunar based. However, certain regions follow the solar calendar as well.
According to the lunar calendar, there are twelve months in a year and each month has 29 or 30 days depending upon the movement of the moon. Each month is split into two fortnights or pakshas. The fortnight of the waxing moon is called the Shukla Paksha or the bright fortnight, whereas the fortnight of the waning moon is called the Krishna Paksha or the dark fortnight. In North India, a new lunar month begins with the day after the full moon. In many parts of South India, a new lunar month begins the day after the new moon.
The twelve months of the Hindu lunar calendars add up to approximately 356 days. To stay in line with the solar calendar (which has 365 days in a normal year and 366 days in a leap year), every few years a leap month is added. Thus, sometimes there are thirteen months in a year, instead of twelve. This leap month is called the Adhik Mas or the Purushottam Mas.
The twelve months in the Hindu calendar are as follows:
Hindu Month Western Month
1. Vaisakh April-May
2. Jyesth May-June
3. Ashadh June-July
4. Shravan July-August
5. Bhaadra August-September
6. Ashwin September-October
7. Kartik October-November
8. Agrahayana November-December
9. Paush December-January
10. Maagh January-February
11. Phalgun February-March
12. Chaitra March-April
The above table gives an approximate relationship between the various months in the Hindu lunar calendar and those in the solar Gregorian calendar, with which we are all familiar.
Different regions in India give their own names to the lunar months. An interesting feature of the Hindu calendars is that different calendars follow different epochs. This means that the year value for a given date in the Gregorian calendar is represented variously in various Hindu calendars.
In 1957, India adopted a new national calendar that is based on the ancient Shaka calendar. Unlike most of the Hindu calendars, this is a solar calendar. However, this calendar was introduced for administrative reasons, and it has no religious significance. This calendar is falling into disuse since most of the official business in India is now carried out using the Gregorian calendar.