Moon Phase Calculator
Work out the Moon's phase for any date, as an estimate.
Quick answer: enter your details below and click Calculate Moon Phase — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
M
500 New Tools
Enter your details below.
How to use
- Enter a date as YYYY-MM-DD.
- Click Calculate Moon Phase.
- Read the phase, the Moon's age, and the approximate illumination.
About this tool
Enter a date and the tool estimates the Moon's age and phase from the known new moon of 6 January 2000, using the average lunar cycle of 29.53 days. Moon phases here are estimates: the real cycle varies slightly, so the phase near a boundary may differ by a day from an astronomical table.
Frequently asked questions
What does Moon age mean?
How many days have passed since the last new moon, on a scale of 0 to about 29.53 days.
Why is illumination only approximate?
It is worked out from the Moon's age on a simple curve, not from the Moon's exact position.