Hindu Lunar Month: Amanta and Purnimanta

In the Amanta system, common in South and West India, a month runs from one new moon to the next. In the Purnimanta system, common in North India, a month runs from one full moon to the next. Both use the same twelve names, from Chaitra through Phalguna, and both agree during Shukla paksha, the waxing fortnight.

They differ only during Krishna paksha, the waning fortnight. A Purnimanta month has already moved on to the next name by then, while the Amanta month keeps its old name until the new moon. So a festival can fall in the same fortnight in every region and still be described with two different month names. Neither label is wrong; they are counting from different starting points.

Each Amanta month takes its name from the sign the Sun occupies at the new moon that opens it. When the Sun is in sidereal Pisces at that new moon, the month is Chaitra. When the Sun is in Aries, it is Vaishakha, and the pattern continues around the zodiac until Aquarius, which gives Phalguna.

Now and then the Sun stays in one sign for an entire lunar month, so no solar ingress, or sankranti, happens inside it. That month is called Adhika, meaning extra, and it borrows the name of the month that follows. It appears roughly once every two and a half to three years and keeps the lunar calendar aligned with the seasons.

The page shows the Amanta month, the Purnimanta month, whether the month is Adhika, the tithi and paksha at sunrise, and the times of the new moons before and after the date. The new moon times bracket the current Amanta month, so you can see how far into it the date falls. If you follow a regional calendar, pick the system your family or temple uses and read that line.

The month is read at local sunrise for the place you enter, because a Hindu calendar day takes its character from the sunrise that opens it. A different city can change the answer on a day near a new moon.

Positions are sidereal with the Lahiri ayanamsa. New moons are located from the Moon to Sun angle, searched a day at a time and then narrowed to about one minute. The rare Kshaya case, where a month is dropped, is not handled separately. The calculation runs in our own engine.