If you've ever wondered why Diwali falls on a different date every year, or why your grandmother checks the “tithi” before planning a ceremony — this guide is for you. The Hindu calendar is a beautiful system that's been tracking time for thousands of years, and once you understand the basics, everything about Hindu festivals and traditions starts to make more sense.
Solar vs. Lunar: Two Systems in One
The Hindu calendar is actually a lunisolar calendar — it uses both the sun and the moon to measure time. The months are based on the moon (lunar), but the year is kept in sync with the sun (solar) through occasional adjustments.
This is why Hindu festivals “move around” on the Western (Gregorian) calendar. They don't change in the Hindu calendar — Diwali is always on Amavasya (new moon) of Kartik month. It just falls on a different Gregorian date each year because the two calendars measure months differently.
The Lunar Month
A Hindu lunar month runs from one new moon to the next (or one full moon to the next, depending on the regional tradition). Each month is divided into two halves called pakshas:
- Shukla Paksha (bright half) — the 15 days from new moon to full moon, when the moon is waxing
- Krishna Paksha (dark half) — the 15 days from full moon to new moon, when the moon is waning
Each day within a paksha is called a tithi. There are 15 tithis in each paksha, named Pratipada (1st), Dwitiya (2nd), Tritiya (3rd), and so on up to Purnima (full moon) or Amavasya (new moon).
The 12 Hindu Months
The Hindu year has 12 months, each roughly 29.5 days long. The names vary slightly by region, but the most common (North Indian) names are:
- Chaitra (March-April)
- Vaishakha (April-May)
- Jyeshtha (May-June)
- Ashadha (June-July)
- Shravana (July-August)
- Bhadrapada (August-September)
- Ashvin (September-October)
- Kartik (October-November)
- Margashirsha (November-December)
- Pausha (December-January)
- Magha (January-February)
- Phalguna (February-March)
The Leap Month (Adhik Mas)
Since 12 lunar months add up to only about 354 days (compared to the solar year's 365), the Hindu calendar periodically inserts an extra month called Adhik Mas (also known as Purushottam Mas). This happens roughly every 32 months and keeps the lunar calendar aligned with the seasons.
Samvat: The Hindu Year Number
The Hindu calendar has its own year numbering systems, the most common being the Vikram Samvat. The Vikram Samvat is about 57 years ahead of the Gregorian calendar — so the year 2026 CE corresponds roughly to Vikram Samvat 2082-2083. The Hindu New Year begins in Chaitra (March-April) in most North Indian traditions, and in Kartik in some other traditions.
Why This Matters for Everyday Life
Understanding the Hindu calendar helps you:
- Know festival dates — check the festival calendar to see what's coming up
- Plan ceremonies — weddings, griha pravesh, and other rituals are scheduled based on auspicious tithis and nakshatras
- Observe fasting days — Ekadashi, Pradosh, and other vrats follow the tithi cycle
- Check the daily panchang — the five key elements of each day (tithi, vara, nakshatra, yoga, karana) help determine auspiciousness
Regional Differences
India is vast, and different regions follow slightly different calendar traditions. The two main systems are:
- Amanta (new moon ending) — used in Gujarat, Maharashtra, and most of South India. Months end on the new moon (Amavasya).
- Purnimanta (full moon ending) — used in North India and Nepal. Months end on the full moon (Purnima).
Both systems track the same astronomical events — they just differ in where they draw the month boundary. Most festivals fall on the same day regardless of which system you follow.