Tithi: the lunar day, and how it is calculated

Twelve degrees of Moon–Sun separation

Seen from Earth, the Moon moves eastward around the sky about thirteen times faster than the Sun. Measure the angle by which the Moon is ahead of the Sun along the ecliptic — the elongation — and divide the full circle into 30 parts of 12°. Each part is a tithi.

• At new Moon the elongation is 0° and the first tithi, Shukla Pratipada, begins.
• The fifteen tithis of the waxing half (Shukla paksha) end with Purnima, the full Moon, at 180°.
• The fifteen of the waning half (Krishna paksha) end with Amavasya, the new Moon, at 360°.

A lunar month averages about 29.5 days, so a tithi averages a little under 24 hours. The Moon’s speed changes along its elliptical orbit, so real tithis are longer or shorter: in the month from 20 October 2026 they last between 20 h 00 min and 26 h 41 min.

Because only the difference between the Moon and the Sun matters, the tithi is the same in the sidereal and the tropical zodiac: no ayanamsha is involved.

Worked example

The thirty tithis

Months are counted either from new Moon to new Moon (amanta, common in southern and western India) or from full Moon to full Moon (purnimanta, common in the north). The tithis are the same; only the month name attached to the waning half differs.

The tithi of the day: sunrise, kshaya and vriddhi

Calendars name a civil day by the tithi in effect at local sunrise (udaya tithi). Since a tithi can be shorter or longer than the time between two sunrises, two special cases follow:

• Kshaya (lost) tithi: it begins after one sunrise and ends before the next, so it never names a day. In Bengaluru, 27 October 2026 opens with Krishna Pratipada, and Krishna Dvitiya comes and goes before the next sunrise.
• Vriddhi (increased) tithi: it spans two sunrises, so two consecutive days carry the same tithi. In Bengaluru, Shukla Navami is in effect at sunrise on 18 November 2026 and again the next morning.

Sunrise differs by city, so a tithi can be kshaya in one city and not in another. That is one reason festival dates can differ between regional calendars.

Why panchangas differ by a minute or two

Every panchanga computes the same elongation, but lunar theories and rounding differ. Against Drik Panchang on 28 city-and-date combinations, this website’s tithi endings were within 2.3 minutes — always slightly later — and every tithi name matched. Near a boundary, those minutes can decide which tithi holds at sunrise, so treat any printed ending time as good to a few minutes.

Try any date and city in the live Panchang; its “About this result” panel lists the settings.