Moon Phase Calculator

The moon phase on any date can be calculated using the synodic period (29.53 days) — the time for the Moon to return to the same phase. Starting from a known New Moon date, you calculate how many days have elapsed and where that falls in the lunar cycle.

1. 1Use a known New Moon as a reference (e.g., 6 January 2000)
2. 2Calculate days elapsed from reference to target date
3. 3Divide by synodic period (29.53058 days) and take the remainder
4. 4The remainder tells you the phase: 0=New, 7.4=First Quarter, 14.8=Full, 22.1=Last Quarter