Moon Phase Calculator
The Hindu calendar does not divide the Moon into eight phases. It divides it into thirty tithis — each one the time the Moon takes to gain twelve degrees on the Sun — grouped into a waxing and a waning fortnight. This page finds the tithi and paksha of your birth.
What this calculator works out
- The tithi at your birth
- One of thirty lunar days, defined by the angle between the Moon and the Sun.
- Paksha
- Whether you were born in the waxing (Shukla) or waning (Krishna) fortnight.
- Illumination
- How much of the Moon's disc was lit, as a percentage.
- Moon sign and nakshatra
- Where the Moon actually sat, alongside its phase.
How it works
Tithi is the angular distance between the Moon and the Sun, divided by twelve. Because both bodies move at varying speeds, a tithi is not a fixed length: it runs anywhere from about nineteen to twenty-six hours, which is why the tithi of a birth does not map neatly onto a calendar date.
Step by step
- The birth moment is converted to Universal Time and then to a Julian Day.
- Sidereal longitudes of the Sun and Moon are computed for that instant.
- The elongation — the Moon's longitude minus the Sun's — is taken.
- That angle is divided by 12°. Each full 12° step is one tithi, giving thirty across the lunar month.
- The first fifteen fall in Shukla paksha, the second fifteen in Krishna paksha.
A worked example
Input: Moon at 214°, Sun at 98°
- Elongation = 214 − 98 = 116°
- 116 ÷ 12 = 9.67, so the 10th tithi is running
- 116° is under 180°, so the Moon is still waxing → Shukla paksha
Result: Shukla Dashami — the tenth tithi of the bright fortnight.
How to read your result
- A tithi is not a phase
- Western astrology divides the Moon into eight visual phases. The Hindu calendar divides it into thirty precise angular steps, and festivals, vrats and muhurats are scheduled by those — Diwali falls on Amavasya, a tithi, not on a fixed date.
- Tithis are not equal in length
- Because both bodies move at varying speeds, one tithi runs anywhere from about nineteen to twenty-six hours. This is why a tithi does not map cleanly onto a calendar date.
- Birth near Amavasya or Purnima is read differently
- Some traditions weigh the Moon's strength by its distance from the Sun, which makes the tithi one input into how the Moon is judged in a chart.
What changes the answer
- Birth time matters here — a tithi can begin and end at any hour, so two people born on the same date hours apart can have different ones.
- Amavasya is the new moon and Purnima the full moon; both are tithis, not dates.
- The nakshatra and the tithi are separate lunar coordinates and are read for different things.
- Illumination is a derived figure, useful as an intuition check on the tithi rather than as a reading in itself.
Frequently asked questions
How is a tithi different from a moon phase?
A Western phase is one of eight visual descriptions. A tithi is one of thirty precise angular divisions, and it is what Hindu festivals, vrats and muhurats are actually scheduled by. Diwali falls on Amavasya, which is a tithi, not on a fixed date.
What do Shukla and Krishna paksha mean?
Shukla paksha is the bright fortnight, from new moon to full. Krishna paksha is the dark fortnight, from full moon back to new. Each contains fifteen tithis.
Does my birth tithi matter astrologically?
It is used — some readings weigh the strength of the Moon by its distance from the Sun, and a birth close to Amavasya is read differently from one at Purnima. It is one input among many, not a reading in itself.
Why does the tithi depend on my birth time?
Because a tithi can begin and end at any hour. Two people born on the same calendar date, hours apart, can genuinely have different tithis.
Related astrology concepts
- Nakshatra calculator — the other lunar coordinate
- Today's panchang — the current tithi and the rest of the five limbs
- Hindu calendar — how tithis drive festival dates
Related calculators
Today’s panchang · Hindu calendar · More kundli & birth chart calculators