Moon Phase Calculator
Find the moon phase, illumination and moon age for any date — plus the dates of the next new moon and full moon.
How to use
- 1Pick a date (or leave empty for today).
- 2See the phase, how much of the Moon is lit and when the next full and new moons are.
How it's calculated
Moon age = days since a known new moon (6 Jan 2000, 18:14 UTC) modulo the mean synodic month of 29.530589 days. Illumination = (1 − cos(2π × age ÷ 29.53)) ÷ 2.
Frequently asked questions
How accurate is this?
It uses the Moon's average cycle, so phase dates can be off by up to about half a day compared with precise astronomical tables.
Why is the lunar month 29.5 days?
That's the synodic month — the time for the Moon to return to the same phase, longer than its 27.3-day orbit because Earth also moves around the Sun.
Is the phase the same everywhere on Earth?
Yes, the phase is global, though the Moon appears rotated in the Southern Hemisphere.