The Hindu Calendar, Explained for Yoga Students

Every year somebody asks why Shivarātri moved, and the answer is that it did not. The Gregorian date moved, because the two calendars count different things.

Once the mechanics are clear, every festival date becomes predictable, the practice days become legible, and it stops being necessary to look up whether something has happened yet.

The Basic Problem

A lunar month is about 29.5 days. Twelve of them make about 354 days. A solar year is about 365.25.

So a purely lunar calendar drifts against the seasons by roughly eleven days a year, which is how the Islamic calendar works and why Ramadan moves through the seasons. A purely solar calendar keeps the seasons and loses the moon.

The Hindu calendar is lunisolar: it counts lunar months and corrects them against the solar year. That correction is why dates appear to move within a range and then come back.

The Correction

The mechanism is an extra month.

Roughly every two and a half to three years, a thirteenth month is inserted, called adhika māsa, the additional month. It takes the name of the month it doubles, with adhika prefixed.

What this accomplishes. The eleven-day annual drift accumulates for a few years and is then absorbed by an extra month, which pulls the lunar reckoning back into alignment with the solar seasons. Festivals therefore move within a window of a few weeks against the Gregorian calendar and do not wander through the year.

Two practical consequences. In a year with an extra month, festivals after the insertion fall later than usual. And an adhika māsa is traditionally treated as unsuitable for certain auspicious activities, which is worth knowing if anyone mentions it.

Tithi: The Lunar Day

This is the concept that makes everything else work, and it is not a day in the ordinary sense.

A tithi is twelve degrees of angular separation between the moon and the sun. Thirty tithis make a lunar month, since thirty times twelve is 360.

So a tithi is not twenty-four hours. It is however long the moon takes to gain twelve degrees on the sun, and the moon's orbital speed is not constant. A tithi runs roughly between nineteen and twenty-six hours.

Three things follow, and they explain most of the confusion people have about these dates.

A tithi can begin and end at any hour. It does not align with sunrise or midnight.

So one Gregorian date can contain parts of two tithis, and occasionally a tithi is skipped or repeated relative to civil days.

And a festival is on a tithi, not on a date. Which means the rule for determining when it falls has to specify which tithi, and sometimes which part of it, and that is why authorities occasionally differ by a day.

That last point is the answer to why two temples can observe something on different days. They are applying different rules about which civil day a tithi belongs to.

Paksha: The Two Fortnights

The lunar month divides in two.

Śukla pakṣa, the bright fortnight: the waxing moon, from new to full.

Kṛṣṇa pakṣa, the dark fortnight: the waning moon, from full to new.

Each runs fifteen tithis. So a date in this system is specified as a month, a pakṣa, and a tithi number: for example the fourteenth tithi of the dark fortnight, which is when Mahā Śivarātri falls.

The two full-moon and new-moon days have their own names and their own practice significance, treated in the article on them.

Where the Month Begins

A complication worth knowing, because it explains regional disagreements.

Amānta reckoning ends the month at the new moon. Used in western and southern India.

Pūrṇimānta reckoning ends it at the full moon. Used in much of the north.

The consequence: the same dark fortnight belongs to different months under the two systems, so a festival in a dark fortnight can be named for one month in Maharashtra and another in Uttar Pradesh while falling on the same day. The date is the same; the label differs.

The Five Limbs

Pañcāṅga, the almanac, means five limbs, and those are what it tabulates.

Tithi. The lunar day, twelve degrees of moon-sun separation.

Vāra. The weekday. The only one of the five requiring no computation, and the one that matches the seven *graha*s.

Nakṣatra. The lunar mansion the moon occupies. Twenty-seven of them, each thirteen degrees twenty minutes, covering the full circle. These are the divisions that produce the number 108 when quartered.

Yoga. A quantity derived from the combined positions of sun and moon, twenty-seven of these as well, each of the same angular size as a nakṣatra. Not related to the practice despite the shared name.

Karaṇa. Half a tithi, so six degrees of separation.

A pañcāṅga is a table of these five for each day, and consulting one is how anybody actually determines a date. A practitioner who learns to read the first three has most of what is useful.

The Twelve Months

Worth listing, since the names appear constantly in festival rules and are otherwise opaque.

Caitra (March–April), Vaiśākha, Jyeṣṭha, Āṣāḍha, Śrāvaṇa, Bhādrapada, Āśvina, Kārtika, Agrahāyaṇa or Mārgaśīrṣa, Pauṣa, Māgha, Phālguna (February–March).

Two things worth noticing.

The month names come from nakṣatras. Each is named for the lunar mansion in which the full moon of that month falls. Caitra from Citrā, Vaiśākha from Viśākhā, and so on. The naming is astronomical.

And the Gregorian ranges are approximate. Each lunar month straddles two Gregorian ones, and which two shifts by a few weeks depending on where the year sits in its cycle.

Where the festivals in this cluster fall, by rule:

Learn that table and a pañcāṅga, and nothing in the cluster requires looking up twice.

How to Work Out When Something Falls

Practically, in order.

Learn the rule, not the date. Mahā Śivarātri is the fourteenth of the dark fortnight of a particular month. Navarātri begins on the first of the bright fortnight of Āśvina. Holi is the full moon of Phālguna. Makar Saṅkrānti is solar and therefore fixed at 14 January most years.

Then consult a panchang for the year. Any reliable almanac or its online equivalent will give the civil date. The rule plus a current table is the whole method.

Expect a day of variation. Different authorities apply different conventions about which civil day a tithi belongs to. If two sources differ by one day, neither is necessarily wrong.

And for anything solar, the date is nearly fixed. Saṅkrānti days track the sun's entry into a sign, so they fall on nearly the same Gregorian date each year and drift only very slowly.

The Years

Briefly, since students see the numbers and are confused by them.

Vikram Saṃvat runs about 57 years ahead of the Common Era, so 2026 CE is roughly 2083 VS.

Śaka Saṃvat, the Indian national civil calendar's era, runs about 78 years behind, so 2026 CE is roughly 1948 Śaka.

And the named sixty-year cycle gives each year a name rather than a number, which is why a temple notice may name a year you cannot place.

Multiple eras in concurrent use is normal, and the Gregorian year is used alongside them for all civil purposes.

What a Practitioner Can Use

The rule for the festivals you care about. Four or five rules cover nearly everything, and then no annual lookup is a mystery.

Tithi as the unit. Not a day. Nineteen to twenty-six hours, beginning at any hour, which explains every apparent inconsistency in these dates.

The fortnights for practice. Waxing and waning are the basic rhythm, and ekādaśī, the eleventh of each, occurs twice a month on that reckoning.

And a panchang. Printed or digital. It is the reference the whole system runs on, and reading the first three columns is a short skill with a long payoff.

Frequently Asked Questions

Why do Hindu festival dates change every year?

Because they are set by a lunisolar calendar and reported in a solar one. The festival falls on the same lunar date each year; the Gregorian equivalent moves.

What is a lunisolar calendar?

One that counts lunar months and corrects them against the solar year, so the months stay roughly aligned with the seasons instead of drifting through them.

How is the correction made?

By inserting a thirteenth month, adhika māsa, roughly every two and a half to three years. It absorbs the accumulated eleven-day annual drift.

What is a tithi?

Twelve degrees of angular separation between the moon and the sun. Thirty make a lunar month, and because the moon's speed varies, a tithi runs roughly nineteen to twenty-six hours.

Why is that important?

Because a tithi is not a civil day and can begin at any hour. A festival falls on a tithi, so the rule has to specify which civil day that tithi belongs to, which is why authorities sometimes differ by a day.

What are shukla and krishna paksha?

The two fortnights. Śukla is the waxing moon from new to full; kṛṣṇa is the waning moon from full to new. Each runs fifteen tithis.

Why do northern and southern calendars name months differently?

Because amānta reckoning ends the month at the new moon and pūrṇimānta ends it at the full moon. The same fortnight therefore belongs to different months, so the day is the same and the label differs.

What are the five limbs of a panchanga?

Tithi, the lunar day; vāra, the weekday; nakṣatra, the lunar mansion; yoga, a derived quantity from the two luminaries' positions; and karaṇa, half a tithi.

Is the yoga in panchanga the same as yoga the practice?

No. It is a calculated quantity of thirteen degrees twenty minutes derived from the sun and moon positions, and the shared name is unrelated to the practice.

Where do the month names come from?

From the nakṣatra*s. Each month is named for the lunar mansion in which its full moon falls, so *Caitra comes from Citrā and Vaiśākha from Viśākhā. The naming is astronomical.

How should a student find out when a festival falls?

Learn the rule, which is a month, a fortnight and a tithi number, then consult a pañcāṅga for the year. Expect occasional one-day variation between authorities.

Learn Four Rules, Not Forty Dates

Nothing about these dates is arbitrary. A lunar month runs about 29.5 days, twelve of them fall eleven days short of a solar year, and a thirteenth month is inserted periodically to fix it. A tithi is twelve degrees of separation between moon and sun, which makes it between nineteen and twenty-six hours long and able to start at any time of day. Every apparent inconsistency in Hindu festival dates follows from those two facts, and a pañcāṅga resolves the rest.

Rohit Yoga Academy runs a residential 200-hour Yoga Teacher Training in Swargashram, Rishikesh, where the festivals that fall during a course are explained as they arrive.