Moon Phase Calculator
Find the moon phase for today or any date: illumination percent, lunar age, moon distance, and exact times of the next new moon, first quarter, full moon, and
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What is Moon Phase Calculator?
The Moon Phase Calculator shows the appearance of the moon for any date and time using standard astronomical algorithms, entirely offline. It computes the phase name, the illuminated fraction of the disc, the lunar age since the last new moon, the moon’s distance from Earth, and the exact dates of the next four major phase events, with a live preview of the moon that flips correctly for the southern hemisphere.
Key Benefits
- Plan moonlight-sensitive activities such as night photography, stargazing, fishing, or beach walks
- Track lunar dates for cultural and religious calendars such as Buddhist observance days and full moon festivals
- Get new moon and full moon times accurate to the minute, not just the date
- Fully offline and private — the math runs in your browser with no API calls
Common Use Cases
- •Picking a dark-sky night around the new moon for astrophotography
- •Scheduling full-moon hikes, Loy Krathong, or other moon festivals
- •Checking the moon phase for a wedding date, fishing trip, or night run
- •Answering the question of what phase the moon is in today for homework or curiosity
How to Use the Moon Phase Calculator
- Pick a moment: Leave the field on the current time for tonight’s moon, or enter any date and time you are curious about.
- Read the phase: See the phase name, how much of the disc is lit, the lunar age since the last new moon, and a live rendering of the moon.
- Check upcoming events: Scroll to the event list for exact dates and countdowns to the next new moon, first quarter, full moon, and last quarter.
- Adjust and copy: Switch the hemisphere toggle to flip the view for the southern sky, then copy a text summary of the results.
Key Features
- Phase angle and illumination from Meeus truncated series, accurate to about 0.1 percent
- Exact times for the next new moon, first quarter, full moon, and last quarter
- Countdowns to every event and a progress bar across the 29.53-day synodic month
- Hemisphere toggle flips the moon rendering for southern-horizon viewers
- Moon distance in km and miles plus the apparent angular diameter
Frequently Asked Questions
How accurate are the phase times?
Event times use truncated series from Meeus’ Astronomical Algorithms and are typically accurate to within a few minutes of full astronomical calculations — far more precision than planning around the moon ever needs.
Does the calculator need an internet connection?
No. All math runs as plain JavaScript in your browser, so the page keeps working offline once loaded. No API calls, no location data, nothing uploaded.
Why does the moon look backwards?
From the southern hemisphere the moon is viewed from the other side, so the lit part appears mirrored. Use the hemisphere toggle to flip the rendering to match your sky.
What does lunar age mean?
Lunar age is the number of days since the most recent new moon, running from 0 to 29.53. First quarter is about day 7.4, full moon around day 14.8, and last quarter near day 22.1.