Curious what the moon looked like on the night you were born, or what phase it’ll be in on an upcoming camping trip (full moons mean brighter nights, new moons mean darker skies for stargazing)? The Moon Phase Calculator answers instantly for any date, past or future.
The eight phases
The moon cycles through eight named phases roughly every 29.53 days (the “synodic month”):
- New Moon — fully dark, ~0% illuminated
- Waxing Crescent — growing, ~25%
- First Quarter — half-lit, growing
- Waxing Gibbous — growing, ~75%
- Full Moon — fully lit, ~100%
- Waning Gibbous — shrinking, ~75%
- Last Quarter — half-lit, shrinking
- Waning Crescent — shrinking, ~25%
How the calculation works
This tool uses Conway’s Moon Phase Algorithm, a well-known astronomical approximation that computes how many days have elapsed since a known reference new moon, divides by the average synodic month length, and maps the fractional remainder to one of the eight phases. It’s accurate to within about a day — precise enough for reference purposes, planning, or curiosity, though not for professional astronomical work (which accounts for the moon’s slightly variable orbital speed).
We verified the algorithm against multiple documented historical new-moon and full-moon dates before shipping it, confirming it lines up correctly.
One phase, anywhere on Earth
A common misconception: the moon’s phase doesn’t depend on where you’re standing. Everyone on Earth sees the same phase at the same moment (though the exact rise/set time and visible orientation differ by location and hemisphere).
Try it yourself
Pick a date on the Moon Phase Calculator and get an instant visual answer with an emoji moon icon — no app download, no ads, no tracking.