๐ Moon Phase Calculator
Enter a date to see the calculation
* The calculation corrects for the main irregularities of the Moonโs orbit; new and full moon times are typically within an hour.
Enter a date and calculate the moon's age (days since the last new moon), phase (new moon, first quarter, full moon, last quarter, etc.), and how much of it appears illuminated. Useful for stargazing or planning a moon-viewing event.
How to use
- Enter the date you want to check.
- The moon phase, age, and illumination percentage are shown automatically.
How the calculation works
Enter a date to see the Moon at noon on that day in your deviceโs time zone. Moon age: days since the last new moon (0 to about 29.5) Phase: the name, such as new moon, crescent, first quarter, full moon or last quarter Illumination: the fraction of the visible disc that is lit The lunar cycle (synodic month) averages 29.53 days, but because the Moonโs orbit is elliptical and pulled by the Sun, real new and full moons come up to about half a day earlier or later than the average. This tool calculates the SunโMoon angle (elongation) with the main correction terms, so it follows these swings. The moon age is the time since the calculated moment of the last new moon.
Worked example
September 19, 2026 (noon, Japan time) Moon age about 8.0 days, first quarter, about 53% lit September 26, 2026 Moon age about 15.0 days, full moon, about 100% lit (The exact full moon falls in the early hours of September 27 in Japan.) October 10, 2026 Moon age about 29.0 days, just before new moon and almost invisible
Things to be aware of
- A moon age around 15 does not always mean full moon that day. The date of the full moon depends on when the exact moment falls.
- Weather and moonrise and moonset times are not included.
- Traditional Japanese moon names such as Jลซsanโya and Jลซgoya follow dates in the old lunisolar calendar rather than moon age, so they can be a day off from this toolโs moon age.
FAQ
How accurate is this calculation?
It corrects for the main effects of the Moonโs elliptical orbit and the Sunโs pull, so new and full moon times are typically within an hour. For precise observation planning, also check a published almanac.
Does this account for time zones?
Yes. It calculates for noon on the entered date in your deviceโs time zone.
Can I check dates in the past or future?
Yes, any date works. For dates several centuries away the error slowly grows.