Lunar Phase Calculator
Choose a date to estimate the Moon’s phase, age in its synodic cycle, and visible illumination.
A QUICK WALKTHROUGH
How to use this tool
- Enter a calendar date between 1900 and 2100.
- Select Calculate to estimate the lunar phase for that UTC calendar date.
- Read the precision note before using the result for observation planning or historical work.
Local approximation
This browser-only calculator uses a fixed 2000-01-06 new-moon epoch and the mean synodic month of 29.530588853 days. It is an educational estimate, not an ephemeris or authoritative calendar.
Date convention
The date is treated as midnight UTC. Results can differ from local observing conditions and exact astronomical event times.
GOOD TO KNOW
Common questions
How accurate is it?
It usually identifies the broad phase well, but the simple mean-cycle model can differ from exact event times by hours or more.
Does it use my location?
No. It uses only the selected calendar date and does not calculate local rise, set, or visibility.