Moon phase calculator

The moon’s phase is how much of its sunlit half we can see from Earth. As the moon goes round us every 29.53 days on average, it moves from new moon (Amavasai, unlit) through the first quarter to full moon (Pournami, fully lit) and back through the last quarter. This free tool shows the phase on any date from 1000 to 3000, how much of the moon is lit, the tithi, moonrise and moonset for your city, the next Pournami and Amavasai, supermoons and the next eclipses.

Planning Girivalam from Villupuram

Murugan, a bus conductor in Villupuram, walks Girivalam round the hill at Tiruvannamalai on most full moons. He needs to know which night to swap his shift. He opens the tool on today’s date, keeps Chennai as the nearest city, and reads the callout under the answer: Pournami tithi runs from Sunday 25 October, 11:56 am, to Monday 26 October, 9:42 am. The walk follows the tithi, so Sunday night is the night. The Next 12 phases table then lists the coming Pournamis for the rest of the season, with the Karthigai Pournami on 24 November marked as a supermoon.

What each figure means

How it is worked out

• Phase times use the method in Jean Meeus’s Astronomical Algorithms (2nd edition, 1998, chapter 49): an average cycle of 29.530589 days, corrected by the main terms for the sun’s and moon’s orbits and small planetary terms, then turned from astronomical time into clock time with the measured difference between the two (ΔT).
• Moon position, tithi, moonrise and distance use Meeus chapter 47 for the moon and the VSOP87 theory for the sun. Moonrise is the moment the centre of the moon meets the horizon, the way drikpanchang.com times it.
• Supermoon: a full moon closer than 362,500 km; a micromoon farther than 405,000 km. Lists online differ (some use 360,000 km, others 90% of the way to the closest point of that orbit), so one list may call a moon “super” and another not.
• Eclipses use Meeus chapter 54 for the kind, the time of greatest eclipse and its size. For lunar eclipses the tool checks whether the moon is above your horizon; for solar eclipses it follows the moon across the sun as seen from your city and gives how much of the sun’s width it covers.

How accurate is it?

Phase times were checked against the PyEphem astronomy library for every new and full moon from 1900 to 2100: the largest difference was 2.8 minutes. Moonrise and moonset for Chennai on 21 October 2026 (2:26 pm and 2:19 am) match drikpanchang.com to the minute, and Pournami tithi times agree with Drik within a minute (checked October 2026 for Chennai, Madurai and Delhi). The 2026 eclipses match NASA’s eclipse list (for example the total lunar eclipse of 3 March 2026, greatest at 11:34 UT, which is 5:04 pm IST) to within a minute or two.

Common mistakes

• Expecting Pournami on the date of the full moon. A panchang names the day by the tithi at sunrise, and Girivalam follows the tithi span, so the night before the exact full moon is often the one.
• Reading another country’s times. The phase is the same moment everywhere, but the clock time and sometimes the date change. Cities outside India are shown in standard time: add an hour in summer.
• Calling every bright full moon a supermoon. Only a few full moons a year come that close.
• Assuming every eclipse is visible from India. Many happen when the moon or sun is below our horizon; the Eclipses table says what your city will see.

Type a birthday in the date to see the moon on the night you were born.