What is the Moon Phase Calculator?
Find the moon phase for any date with this free moon phase calculator. Get the phase name, illumination percentage, moon age, waxing or waning status, and days until the next new or full moon. Covers all eight lunar phases from new moon to full moon. Runs entirely in your browser with no signup.
How to use the Moon Phase Calculator
- Enter a year, month, and day.
- Click Calculate to see the moon phase for that date.
- Review illumination %, moon age, and waxing/waning status.
- Check days until the next new moon and full moon.
- Copy results and calculation steps.
Common use cases
- Checking tonight's moon phase for stargazing
- Finding when the next full moon falls for event planning
- Teaching the lunar cycle in a science classroom
Frequently asked questions
- How is moon phase calculated?
- The calculator uses the synodic month (29.53 days) and a reference new moon on January 6, 2000. Moon age is the days elapsed mod one lunar cycle, and illumination follows (1 − cos(2π × age / month)) / 2.
- What are the eight moon phases?
- New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent — each spanning about 3.7 days.
- What does moon age mean?
- Moon age is the number of days since the last new moon. It ranges from 0 at new moon to about 14.77 days at full moon, then back toward 29.53 days.
- How accurate is this calculator?
- It provides a good approximation suitable for calendars, education, and planning. For precise astronomical event times to the minute, use an ephemeris or observatory data.
