A panchang is calculated from two numbers: the Sun's longitude and the Moon's. Moon minus Sun gives tithi and karana, the Moon alone gives nakshatra, and Moon plus Sun gives yoga, while vara is just the weekday. No other planet takes part. Because tithi is a difference, the ayanamsa cancels out of it, whereas nakshatra carries one ayanamsa and yoga carries two.
Every festival date you have been quoted came out of a calculation that fits on a napkin. Two positions go in, a few subtractions happen, and the Sanskrit comes out the other end. Plenty of people assume a panchang must draw on the whole chart, all nine grahas, because that is how astrology usually gets described. It doesn't.
A panchang is calculated by finding the Sun's and Moon's longitudes for a given place and moment, then deriving tithi, nakshatra, yoga and karana from those two numbers, with vara added as the plain weekday. The five limbs are defined in their own post, so this one is about the machinery underneath them.
How is a panchang calculated?
The almanac maker takes the Sun's and Moon's longitudes and applies three formulas. Moon minus Sun gives tithi and karana, the Moon alone gives nakshatra, and Moon plus Sun gives yoga. Vara is the weekday, a count that needs no sky at all.
The Moon covers roughly 13 degrees of the zodiac a day and the Sun about one, so the gap between them widens by around 12 degrees daily. That is why a tithi, which is a 12 degree slice of the gap, lasts close to a day. It can run anywhere from about 19 to 26 hours, because the Moon speeds up and slows down along its orbit.
Nothing in a printed panchang is a single reading. The maker works through time, finding each moment when one of the running values crosses a boundary, such as the gap passing 84 degrees to end the seventh tithi. Those crossings are the end times on the page. Which tithi then counts for a particular date depends on where sunrise falls, which is the reason festival dates get argued over, and why a tithi and a date are not the same thing covers that part.
Why does the ayanamsa change some limbs and not others?
Tithi and karana are differences, and a difference cancels any offset applied to both bodies. Nakshatra shifts by one ayanamsa, and yoga, which adds the two longitudes, shifts by two.
Sidereal longitudes are the tropical ones minus the ayanamsa, an offset of about 24 degrees at present. Subtract the Sun from the Moon and the offset vanishes, so a tithi comes out the same whichever ayanamsa a calendar maker prefers. Nakshatra uses the Moon alone and carries the whole offset. Yoga adds both longitudes and therefore carries it twice.
This explains a pattern you may have noticed when comparing two panchangs. A disagreement of a degree or so in ayanamsa moves a nakshatra boundary by roughly two hours and a yoga boundary by more, while tithi boundaries stay put. If two sources split on a nakshatra but agree on the tithi, the ayanamsa is the first thing to check, and our ayanamsa explainer covers the offset itself.
Why were Jupiter and Saturn left out?
Probably because a calendar needs bodies that change within days, and only the Sun and Moon do. Jupiter takes about 12 years to circle the zodiac and Saturn about 29, which makes them useless for telling today from tomorrow.
Treat that as a reasoned guess, since we have no record of anyone deciding it. The Sun gives the day and the year, the Moon gives the fortnight and the month, and the angle between them gives the phase that anyone can see overhead without an instrument. A tradition that needed to coordinate fasts, weddings and harvest rites across villages had every reason to build on what was visible and fast.
Eclipses are the one place the nodes show up in practice. They are listed as events when they fall, but they are not a limb of the panchang, and the almanac does not need Rahu to know what tithi it is. For a closer look at the half-tithi slots, see the karana guide.
What does this say about the rest of astrology?
It shows that the almanac and the birth chart are different kinds of thing. The almanac is timekeeping you can verify against the sky, and the interpretation of a chart cannot be verified in the same way.
Everything above can be checked. Tithi 15 ends when the Moon is 180 degrees from the Sun, which is a full Moon, and you can confirm that with your own eyes tonight. Nothing comparable exists for a claim that Saturn in the tenth house slows a career. The panchang earns its trust from arithmetic that holds up, and that trust does not automatically carry over to readings built on other parts of the system.
We think the sensible position is to enjoy the calendar for what it is and to treat chart interpretation as a framework for reflection. Is astrology real? goes through where the evidence stands.
Can you check a panchang yourself?
Yes. Tithi 1 begins at the new moon, tithi 15 ends at the full moon, and tithi 30 ends at the next new moon, so the sky tells you whether a panchang is roughly right.
You cannot judge the exact minute of fullness by eye, but you can tell at once if a printed Purnima is a day off. For a precise check, any ephemeris gives you the two longitudes, and subtracting them takes seconds. If the result lands within a degree of a multiple of 12, a tithi is about to turn over, and the nearest end time on the page should agree.
See your own chart, not only the almanac
The panchang uses two bodies. Vedikks builds your birth chart with every graha, explains it in plain language, and remembers what you have already asked so the next answer builds on the last.
Get my chart, freeQuick answers
How is a panchang calculated?
A panchang is calculated by finding the Sun's and Moon's longitudes for a place and moment, then deriving the limbs from them. Moon minus Sun gives tithi and karana, the Moon alone gives nakshatra, and Moon plus Sun gives yoga. Vara is simply the weekday. The printed end times are the moments when each running value crosses a boundary.
Which planets are used in a panchang?
Only the Sun and the Moon. Four of the five limbs are built from their longitudes and the fifth, vara, is the weekday count. Mars, Mercury, Jupiter, Venus, Saturn and the nodes are not used, although eclipses, which involve the nodes, are listed as events when they occur.
Does the ayanamsa change the tithi?
No. Tithi is the Moon's longitude minus the Sun's, so any ayanamsa offset applied to both bodies cancels out. Nakshatra shifts by one ayanamsa because it uses the Moon alone, and yoga shifts by two because it adds both longitudes together.