Moon Phase Calculator

Summary

Enter any date to see the moon phase name, illumination percentage, and a visual diagram.

How it works

1. Enter or pick any date using the date picker.
2. The tool converts the date to a Julian Date Number.
3. It calculates the age of the moon in days within the ~29.53-day synodic cycle.
4. The phase name and illumination percentage are derived from that age.
5. A visual diagram updates to reflect the current shadow/light geometry.

Use cases

• Plan outdoor photography sessions around the full moon.
• Find the next new moon for stargazing or astrophotography.
• Check the lunar phase on a past date (birthday, anniversary, historical event).
• Gardeners following lunar planting calendars.
• Fishermen and hunters who time activities by moon phase.
• Writers and game designers who need accurate lunar lore.

Frequently Asked Questions