In one paragraph
The Hindu calendar counts twelve lunar months, from Chaitra to Phalguna, each running from one new moon to the next (or one full moon to the next, depending on the region). Twelve lunar months come to about 354 days — eleven short of the solar year — so roughly every two and a half to three years an extra month, Adhik Maas, is inserted to bring the calendar back into step with the seasons.
The twelve months
| # | Month | Sun enters | Roughly | Festivals in this month |
|---|---|---|---|---|
| 1 | Chaitra | Mesha (Aries) | March–April | Ugadi / Gudi Padwa, Ram Navami, Hanuman Jayanti |
| 2 | Vaishakha | Vrishabha (Taurus) | April–May | Akshaya Tritiya, Buddha Purnima |
| 3 | Jyeshtha | Mithuna (Gemini) | May–June | — |
| 4 | Ashadha | Karka (Cancer) | June–July | Guru Purnima |
| 5 | Shravana | Simha (Leo) | July–August | Raksha Bandhan, Janmashtami |
| 6 | Bhadrapada | Kanya (Virgo) | August–September | Ganesh Chaturthi |
| 7 | Ashwina | Tula (Libra) | September–October | Navratri, Dussehra (Vijayadashami), Sharad Purnima, Karva Chauth, Dhanteras, Diwali (Lakshmi Puja) |
| 8 | Kartika | Vrishchika (Scorpio) | October–November | Govardhan Puja, Bhai Dooj, Kartik Purnima |
| 9 | Margashirsha | Dhanu (Sagittarius) | November–December | — |
| 10 | Pausha | Makara (Capricorn) | December–January | — |
| 11 | Magha | Kumbha (Aquarius) | January–February | Maha Shivratri |
| 12 | Phalguna | Meena (Pisces) | February–March | Holi |
How a month gets its name
Each lunar month is tied to the Sun. As the year goes on the Sun enters a new sidereal sign roughly every thirty days — an event called a sankranti. The lunar month in which the Sun enters Mesha (Aries) is Chaitra; the month in which it enters Vrishabha (Taurus) is Vaishakha; and so on round the year. This is the rule Astronaad's calendar engine applies.
The names themselves come from the stars. Each month is named after the nakshatra near which its full moon occurs: the full moon of Chaitra falls near Chitra, that of Vaishakha near Vishakha, of Kartika near Krittika, of Magha near Magha, and of Phalguna near the Phalguni stars.
Amanta and Purnimanta: two ways to count the same month
There are two conventions for where a month begins and ends, and India is divided between them.
In the Amanta system a month ends on the new moon (Amavasya). The bright fortnight comes first, then the dark fortnight. This is the convention in Gujarat, Maharashtra, Karnataka, Andhra Pradesh, Telangana and much of the south and west.
In the Purnimanta system a month ends on the full moon (Purnima). The dark fortnight comes first, then the bright fortnight. This is the convention across most of north India — Uttar Pradesh, Bihar, Madhya Pradesh, Rajasthan, Punjab, Haryana and the Himalayan states.
The bright fortnight carries the same month name in both systems. The dark fortnight does not: in the Purnimanta system it already belongs to the next month. So Krishna Janmashtami is "Shravana Krishna Ashtami" in the south and "Bhadrapada Krishna Ashtami" in the north. It is the same night. Festival dates never differ between the two systems — only the label on the fortnight does.
Adhik Maas: the extra month
A lunar month lasts about 29.5 days, so twelve of them fall about eleven days short of a solar year. Left alone, the festivals would drift backwards through the seasons, as they do in a purely lunar calendar.
The correction is built into the naming rule. Since a month is named by the sankranti that occurs within it, occasionally a lunar month passes in which the Sun does not change sign at all. That month has no name of its own. It is treated as an extra month — Adhik Maas, also called Purushottam Maas or Mal Maas — and it takes the name of the month that follows it. The regular month that comes next is then called Nija ("true").
This happens about once every 32 to 33 months — seven times in nineteen years. Festivals are observed in the regular month, not the extra one; the extra month is kept for prayer, fasting and charity, and weddings and other new undertakings are usually not scheduled in it.
The opposite case, a lunar month containing two sankrantis and therefore "losing" a month name (Kshaya Maas), is possible but extremely rare — more than a century can pass between occurrences.
When the year begins
In most of the regions that follow the Amanta system, the lunar new year is the first day of Chaitra's bright fortnight, celebrated as Ugadi in Karnataka, Andhra Pradesh and Telangana and as Gudi Padwa in Maharashtra. Gujarat begins its year on the day after Diwali, in Kartika. Several regions — Tamil Nadu, Kerala, Bengal, Assam, Punjab — keep a solar new year instead, in mid-April, when the Sun enters Mesha.
Two eras are in common use for numbering the years. The Shaka era, used in the Indian national calendar, runs about 78 years behind the Gregorian year. The Vikram Samvat, common in north and west India, runs about 57 years ahead of it.
Why this matters for festival dates
A Hindu festival is not a calendar date but a specification: a month, a fortnight and a tithi. Diwali is the new moon of Ashwina in the Amanta reckoning; Holi is the full moon of Phalguna. Converting that specification to a date in a given year means working out the real new and full moons, naming the months by the Sun's position, and finding the day on which the tithi prevails at the right time. That is the calculation behind every date in Astronaad's festival calendar.
Frequently asked questions
- What are the 12 months of the Hindu calendar?
- Chaitra, Vaishakha, Jyeshtha, Ashadha, Shravana, Bhadrapada, Ashwina, Kartika, Margashirsha, Pausha, Magha and Phalguna. Chaitra falls in March–April and Phalguna in February–March.
- What is the difference between Amanta and Purnimanta?
- In the Amanta system a lunar month ends on the new moon; in the Purnimanta system it ends on the full moon. The bright fortnight has the same month name in both, while the dark fortnight is named one month later in the Purnimanta system. Festival dates are identical.
- What is Adhik Maas?
- An extra lunar month inserted about every 32 to 33 months to keep the lunar calendar aligned with the solar year. It is the lunar month in which the Sun does not move into a new sign, and it takes the name of the month that follows.
- Why do Hindu festival dates change every year?
- Because they are fixed by the lunar month and tithi, not by the solar date. Twelve lunar months are about eleven days shorter than a solar year, so festivals move earlier each year until an extra month pushes them back.
- Are weddings held in Adhik Maas?
- Traditionally, no. The extra month is set aside for worship, fasting and charity, and auspicious beginnings such as weddings and housewarmings are usually scheduled in a regular month.
Work it out for yourself
These tools compute what this guide explains, from real astronomical positions.
- Festival Calendar →Every major festival date, computed from the lunar calendar.
- Amavasya Dates →The new moon that closes each Amanta month.
- Purnima Dates →The full moon that closes each Purnimanta month.
- Panchang →Today's lunar month, fortnight and tithi.
How this guide was written
The reference tables on this page are generated from the same data Astronaad’s calculators run on, so the guide and the tools cannot disagree. Where classical authorities differ, the text says so and names the convention Astronaad follows. Astrology is a traditional system of interpretation: nothing here is medical, legal or financial advice. Spotted an error? Tell us.