Moon Phase Calculator

About the eight moon phases

The Moon completes one full cycle around the Earth every ~29.53 days (a lunar month / synodic month). Astronomers and astrologers alike divide that cycle into eight phases:

1. New Moon — invisible, a time for fresh starts.
2. Waxing Crescent — a thin sliver appears, intentions forming.
3. First Quarter — half illuminated, decision-making and action.
4. Waxing Gibbous — growing toward full, refining and adjusting.
5. Full Moon — completely illuminated, peak energy, culmination.
6. Waning Gibbous — releasing, gratitude, sharing wisdom.
7. Last Quarter — letting go of what no longer serves.
8. Waning Crescent — rest, reflection, surrender before the next cycle.

The math behind this tool is a simple synodic cycle: we count days since a known new-moon reference (6 Jan 2000) and take modulo 29.53059 to find how far through the cycle any date is. It's accurate to within a few hours — plenty for astrology, birth chart interpretation, or spiritual planning.