Moon Phase Calculator
See the moon phase for any date.
How to use
- 1 Pick a date with the date picker.
- 2 Read the phase name, emoji and illuminated percentage.
- 3 Check the moon's age and whether it is waxing or waning.
- 4 See the predicted next new moon and next full moon.
About Moon Phase Calculator
The Moon Phase Calculator tells you what the Moon looked like — or will look like — on any date you choose.
Pick a day and it returns the named phase (from New Moon through the crescents, quarters and gibbous phases to Full Moon), a matching emoji, the percentage of the disc that is illuminated, and the Moon's "age" in days since the last new moon.
It also predicts the next new moon and the next full moon from your selected date, which is handy for planning.
The calculation is based on the synodic month, the 29.53-day cycle from one new moon to the next, anchored to a precise reference new moon.
From your date it works out where the Moon sits in that cycle, then derives the illumination with a cosine curve that runs smoothly from 0% at new moon to 100% at full moon and back.
Because it uses the mean cycle length, results are an astronomical approximation accurate to within a few hours — perfect for calendars, journaling, gardening by the moon, photography planning and satisfying curiosity, though not intended for precise ephemeris or navigation work.
Everything runs locally in your browser with no accounts, uploads or tracking, so it is fast, private and works offline.
Enter a birthday, a future trip date or a historic event and instantly see the Moon that hung over it.
FAQ
How accurate is the moon phase?
It uses the mean synodic month (29.53 days) anchored to a known new moon, so it is an approximation accurate to within a few hours — great for everyday use but not for precise astronomy.
What does "moon age" mean?
Moon age is the number of days since the most recent new moon. It runs from 0 at new moon up to about 29.53, with full moon near the middle of the cycle at roughly 14.8 days.
Does it depend on my location?
The phase and illumination are essentially the same worldwide for a given moment. The emoji uses the Northern-hemisphere orientation; the shape is mirrored as seen from the Southern hemisphere.