Panchang calculation looks mysterious from the outside, but at its heart it is careful astronomy built on just two moving bodies: the Sun and the Moon. Every one of the five limbs of the panchang, namely tithi, nakshatra, yoga, karana and vara, is derived from where those two bodies are in the sky and from the moment the Sun rises at your location. That last part is why relatives in another city or country sometimes keep a vrat on a different date from you. This guide walks through each limb with its standard definition, then explains the udaya tithi rule, kshaya and vriddhi tithis, and why sunrise and geography change the answer.

What a Panchang Is: Five Limbs From Two Bodies

The word panchang (panchanga) means "five limbs". For each day, a Hindu almanac gives five values used for religious observance and muhurta. Four are pure geometry of the Sun and Moon. The fifth, the weekday, is a count of days, but even that count is anchored to sunrise.

None of these units is tied to the clock. They change whenever the sky says they change, and the job of panchang calculation is to find those moments precisely and decide which value belongs to which day.

Tithi: How Tithi Is Calculated From the Moon and Sun

The tithi is the lunar day, and it is defined by the angle between the Moon and the Sun. Take the Moon's longitude, subtract the Sun's longitude, and you get the elongation, a number from 0 to 360 degrees. Every 12 degrees of elongation is one tithi, so a full cycle of 360 degrees contains exactly 30 tithis. That is the whole of how tithi is calculated: divide the elongation by 12, and the whole-number part tells you which tithi is running.

At new moon (Amavasya) the Moon and Sun are together and the elongation is zero. As the Moon pulls ahead, the bright half (Shukla paksha) runs through tithis 1 to 15, ending at full moon (Purnima) when the elongation reaches 180 degrees. The dark half (Krishna paksha) then runs from Pratipada to Chaturdashi, and the cycle closes with Amavasya as the thirtieth tithi.

Because the Moon moves on average about 13 degrees a day and the Sun about 1 degree, the gap between them grows by roughly 12 degrees a day, which is why a tithi is roughly one day long. But the Moon's speed varies along its elliptical orbit, so a tithi can last from about 19 to about 26 hours. This uneven length is the root of almost every "why is the date different" question.

Because the tithi is a difference between two longitudes, the ayanamsa cancels out: tropical or sidereal, the tithi is the same. That is not true of the next two limbs.

Nakshatra and Yoga: Two 13 Degree 20 Minute Divisions

For nakshatra calculation, the zodiac is divided into 27 equal segments of 13 degrees 20 minutes each (27 multiplied by 13 degrees 20 minutes is exactly 360 degrees). The nakshatra is the segment holding the Moon's sidereal longitude, counted from Ashwini at 0 degrees of sidereal Aries. The Moon circles the zodiac in about 27.3 days, so it spends roughly a day in each nakshatra. You can see which nakshatra and sign the Moon is crossing right now on our Moon Transit Now tool.

The yoga (also called nitya yoga) uses the same 13 degree 20 minute unit, but applied to a different number: the sum of the sidereal longitudes of the Sun and the Moon. Add the two, reduce the total to within 360 degrees, divide by 13 degrees 20 minutes, and the result points to one of 27 yogas, from Vishkambha to Vaidhriti.

So two almanacs can disagree on nakshatra or yoga end times while agreeing on the tithi. Vedic calculations on AjmerAstro use the Lahiri ayanamsa. If you want to see how much the choice of ayanamsa moves a position, our explainer on Lahiri vs KP ayanamsa covers it in detail.

Karana and Vara: The Half-Tithi and the Sunrise Weekday

A karana is half a tithi, meaning the time for the Moon-Sun elongation to grow by 6 degrees. A lunar month therefore has 60 karanas, but only 11 karana names. Four of them are fixed (sthira) and appear only once each month: Shakuni, Chatushpada, Naga and Kimstughna, all clustered around Amavasya and the first tithi after it. The remaining seven are movable (chara): Bava, Balava, Kaulava, Taitila, Garaja, Vanija and Vishti. They repeat in that order eight times to fill the other 56 half-tithis. Vishti is the karana popularly called Bhadra, which many families avoid for starting auspicious work.

The vara is the weekday, from Ravivara (Sunday) to Shanivara (Saturday). In Vedic reckoning the vara starts at local sunrise, not midnight. At 3 AM on what your phone calls Sunday, the panchang vara is still Saturday; it becomes Sunday only when the Sun rises. Sunrise as the start of the day runs through the entire panchang.

The Udaya Tithi Rule: Why Sunrise Names the Day

Since tithis last anywhere from about 19 to 26 hours and start at any hour, a single civil day usually contains parts of two tithis. So which one is "the tithi of the day"? The standard answer is the udaya tithi rule: the tithi that is running at the moment of local sunrise is the tithi assigned to that entire day, even if it ends an hour after sunrise. This is what people mean by tithi at sunrise, and it is why a sunrise panchang is the default for most daily listings.

To compute the day's panchang, the calculation broadly follows these steps:

Festivals then add their own rules on top of the udaya tithi. Some observances look at the tithi prevailing at a specific part of the day rather than at sunrise, such as pradosh (the period after sunset), madhyahna (midday) or the time of moonrise. Diwali Lakshmi puja, for example, is traditionally tied to Amavasya during the evening, and Karwa Chauth ends at moonrise. Those windows are local too. See how this plays out in our guides to Kartik Purnima 2026 and the Diwali, Karwa Chauth and Chhath articles linked below.

Kshaya and Vriddhi Tithi: When a Tithi Is Skipped or Repeated

The variable length of a tithi creates two special cases that surprise many people when they see them in a calendar.

Whether a tithi is kshaya or vriddhi depends on sunrise, and sunrise depends on where you are. A tithi that barely touches sunrise in one city can miss it by a few minutes in another, so one place may show a kshaya tithi while another does not. Neither panchang is wrong; they answer the same question for two different horizons.

Why Panchang Differs by City: Sunrise, Latitude and Longitude

The Sun and Moon positions at a given instant are the same for everyone on Earth, to a very close approximation. What changes from place to place is the moment of sunrise, and that is exactly the moment the udaya rule samples. This is the real answer to why panchang differs by city.

If a tithi ends a little after sunrise in an eastern city, that day carries the old tithi there. In a western city where the Sun rises later, the same tithi may already have ended before sunrise, so the day carries the next tithi. Same sky, same instant, different day label. The same effect can shift which day is marked for a vrat. This is why the panchang on AjmerAstro is location-aware: it is calculated for the place you select, on AjmerAstro's own calculation engine, rather than reusing one city's values for everyone. You can check it for your own city on our free daily panchang.

The same logic of place, time zone and ayanamsa explains why a kundali differs between apps.

Time Zones and the Diaspora: Same Tithi, Different Civil Date

The city effect becomes much larger across countries. A tithi begins and ends at one absolute instant for the whole world. But that instant falls at a very different local clock time in Delhi, London and New York, and each place has its own sunrise.

Consider a tithi that begins in the early afternoon, Indian time, well after sunrise in India. In the eastern United States that same instant is still before dawn on the same calendar date. So the US sunrise that morning already falls inside the new tithi, while in India the tithi first meets a sunrise only the next morning. A US family can therefore observe a festival one civil date earlier than relatives in India, even though American clocks are behind. It feels backwards, but it follows directly from the udaya rule. A UK family sits in between and may match India or differ from it, depending on how close the tithi boundary is to sunrise.

So when you read that Diwali falls on November 8, 2026 or Karwa Chauth on October 29, 2026, treat those as dates computed for Indian locations. Families abroad should not assume the date carries over unchanged. The same applies to multi-day observances like Chhath Puja (November 13 to 16, 2026 in India) and to the Navratri sequence covered in our Sharad Navratri and Dussehra guide. Calculate for where you actually are; if your family follows the date of your ancestral town instead, make that choice knowingly.

Calculating for the real place and time is also what makes a birth chart accurate. Beyond the daily panchang, the free kundali and dasha tools are available in English and Hindi.

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