Amavasya and Purnima are the two points that hold the entire Indian lunar month together. Amavasya is the new moon, when the Moon is not visible; Purnima is the full moon. Every other lunar day is counted outward from these two, and a large share of festivals, fasts and ancestral observances are pinned to one or the other. This article explains what each means, how they are calculated, and why they can appear on different dates in different places.
If you want the broader framework these fit into, our Indian festival calendar explainer covers how the lunar and solar cycles are reconciled.
What Amavasya and Purnima Actually Measure
Both are tithis, and a tithi is defined by the angular separation between the Sun and the Moon as seen from Earth. Each tithi covers twelve degrees of that separation, giving thirty tithis in a lunar month.
Amavasya: Zero Degrees
Amavasya is the tithi during which the Sun and Moon share the same celestial longitude. The Moon is between the Earth and the Sun, its illuminated face turned away from us, so it is effectively invisible. It concludes the waning fortnight, Krishna Paksha.
Purnima: One Hundred Eighty Degrees
Purnima is the tithi during which the two are opposite each other, so the Moon is fully lit from our vantage point. It concludes the waxing fortnight, Shukla Paksha. Together the two fortnights make the complete month of about 29.5 days.
Why They Are Not Fixed Length
The Moon orbit is elliptical, so its apparent speed changes. A tithi can therefore run from roughly 19 to 26 hours rather than a neat 24. This is why an Amavasya can begin in the afternoon of one Gregorian day and end in the morning of the next, and why the day it is listed against depends on the rule being applied.
Observances Associated with Amavasya
Amavasya is widely connected with remembrance of ancestors, and with certain fasts and charitable acts. Associations vary by region and community, and the descriptions below reflect common practice rather than any single rule.
Ancestral Rites
Tarpan and shraddha, offerings made in memory of ancestors, are commonly performed on Amavasya. Mahalaya Amavasya, which concludes the Pitru Paksha fortnight, is the most widely observed of these and falls in the period usually corresponding to September or October.
Named Amavasyas
- Mauni Amavasya – falls in the month of Magha, associated with silence and with bathing at sacred rivers.
- Somvati Amavasya – any Amavasya that falls on a Monday, considered particularly significant in several traditions.
- Mahalaya Amavasya – concludes Pitru Paksha and is central to ancestral observance.
- Diwali Amavasya – the new moon of Kartik, on which Lakshmi Puja is performed.
- Shani Amavasya – an Amavasya falling on a Saturday, linked to observances for Shani.
The Kartik one is a useful counterexample to any general assumption that new moons are inauspicious, since it carries one of the most celebrated observances of the year. Our article on why the Diwali date changes explains how that particular Amavasya is pinned down.
Observances Associated with Purnima
Full moon days carry their own cluster of festivals, and several of the best known observances in the calendar fall on one.
Major Full Moon Festivals
| Purnima | Lunar month | Commonly associated with |
|---|---|---|
| Holi Purnima | Phalguna | Holika Dahan, the night before Holi |
| Buddha Purnima | Vaishakha | Birth, enlightenment and passing of the Buddha |
| Guru Purnima | Ashadha | Honouring teachers and gurus |
| Raksha Bandhan | Shravana | Observances between siblings |
| Sharad Purnima | Ashwin | Night vigils, offerings of kheer |
| Kartik Purnima | Kartik | Lamps, river bathing, Dev Deepawali in Varanasi |
Satyanarayan Vrat
Many households observe a Satyanarayan Puja on Purnima, and monthly full moon fasts are kept in a range of traditions. As with all such observances, whether and how a family keeps them is a matter of their own practice.
Why the Date Can Differ Between Regions
Sunrise Decides the Day
In most traditions the tithi present at local sunrise names the day. Because sunrise differs by more than an hour between eastern and western India, the same Amavasya can be assigned to different Gregorian days in different cities. Where an observance has a specific ritual hour, that window may take priority instead.
Month Labels Differ Too
In the Purnimanta convention used across much of north India the month ends at the full moon, while the Amanta convention of the west and south ends it at the new moon. The tithis are identical, but the month name attached to a given Purnima or Amavasya can differ. Our Panchang basics guide explains how to read these entries with their start and end times.
Frequently Asked Questions
Is Amavasya considered inauspicious?
Some traditions avoid starting new ventures on Amavasya, but the picture is not uniform. Diwali, one of the most celebrated observances of the year, falls on an Amavasya. Associations depend heavily on region, community and the specific new moon in question.
How often do Amavasya and Purnima occur?
Each occurs once per lunar month, roughly every 29.5 days, so about twelve or thirteen times a Gregorian year. They are always separated by about a fortnight.
Why does my calendar show Purnima on a different day than another one?
Because the tithi may span two sunrises, and different traditions and city coordinates resolve that differently. Use a Panchang calculated for your own location and follow your community practice.
Using the Two Lunar Days as a Planning Anchor
Beyond their devotional role, Amavasya and Purnima are genuinely useful reference points for anyone trying to make sense of the traditional calendar, because they are the only two tithis that can be verified by simply looking up at the sky.
Counting Forward and Backward
Once you know when a new moon or full moon falls, you can locate any other tithi in that month by counting. The fourth day after a full moon is Chaturthi of the waning fortnight; the eleventh after a new moon is Ekadashi of the waxing fortnight. A great many observances, including the twice monthly Ekadashi fasts and the Chaturthi observances associated with Ganesha, are described in exactly this way rather than by a fixed date.
Reading Festival Descriptions Correctly
Traditional sources rarely say a festival is on a particular date. They say it falls on a named tithi of a named paksha in a named month, for example the Shashthi of the waxing fortnight of Kartik. Learning to parse that structure means you can locate any festival yourself given a Panchang, instead of depending on a pre-compiled list that may not match your region.
A Caution About Published Lists
Generic national calendars flatten regional differences and often pick one convention without saying which. For anything where timing genuinely matters, the safer approach is to read the tithi start and end times for your own city and apply the rule your family or community follows. Where lists disagree by a day, that disagreement is usually a difference of convention rather than a mistake in either source.