Moon Phase Calculator
Pick a date to see the moon phase for that day: the phase name, how many days into the lunar cycle the moon is, and how much of the disc is lit.
How to find the moon phase for a date
- Enter the year, month, and day.
- Read the phase name and emoji for that date.
- Check the moon age in days and the illuminated percentage.
Examples
A full moon
2024-12-15
Full, about 14 days old, roughly 99 percent illuminated.
Frequently asked questions
How is the moon phase calculated?
We measure days since a known new moon (6 January 2000, 18:14 UTC) and divide by the mean synodic month of 29.530589 days to find the moon age, then map that age to a phase.
Why is the result a little different from an almanac?
This uses the mean synodic month, which can differ from the true moon by a few hours. Phase names and illumination are accurate to within a day, which is fine for planning.
What does the illumination percentage mean?
It is the fraction of the moon's visible disc that is lit by the sun: 0 percent at new moon, 100 percent at full moon, and about 50 percent at the quarters.
Which time zone does the date use?
The phase is evaluated at midnight UTC for the date you enter. Because the moon moves slowly, the phase name is the same worldwide on a given day.
What are the eight moon phases?
New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Last Quarter, and Waning Crescent, in that order through the cycle.
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