How do you use this tool?
- Select a date — today's date is pre-filled.
- The moon is instantly shown visually: the bright side represents the illuminated portion.
- Below the moon you'll see the phase name, illumination percentage, lunar age in days, and the date and countdown to the next full moon and new moon.
- Change the date for any past or future day — the result updates in real time.
What does this calculator do?
The moon phase calculator computes the current moon phase, illumination percentage, and lunar age for any date you enter. It also shows whether the moon is waxing or waning, and gives the date and countdown to the next full moon and new moon.
The calculation uses the synodic month (29.53 days) and a Julian Day Number reference. No location required, no server upload — everything runs directly in your browser.
How is the moon phase calculated?
Synodic month: The moon takes an average of 29.530588853 days to travel from new moon to new moon. This is called the synodic month.
Lunar age:
Lunar age = (JD − 2451550.26) mod 29.53JD = Julian Day Number of the selected date. The value 2451550.26 corresponds to the new moon of January 6, 2000.
Illumination:
Illumination = 0.5 × (1 − cos(lunar age × 2π / 29.53))This yields 0 at new moon (0% lit) and 1 at full moon (100% lit).
What are the 8 moon phases?
| Phase | Lunar age | Illumination |
|---|---|---|
| New Moon | 0–1.85 days | ~0% |
| Waxing Crescent | 1.85–7.38 days | 1–49% |
| First Quarter | 7.38–9.22 days | ~50% |
| Waxing Gibbous | 9.22–14.77 days | 51–99% |
| Full Moon | 14.77–16.61 days | ~100% |
| Waning Gibbous | 16.61–22.15 days | 99–51% |
| Last Quarter | 22.15–23.99 days | ~50% |
| Waning Crescent | 23.99–29.53 days | 49–1% |
What is moon phase data used for?
- Moon calendar gardening: Many gardeners plant leafy vegetables during the waxing moon and harvest during the waning moon — a practice rooted in long-standing observation.
- Fishing: Full moon and new moon are traditionally considered the best fishing times, as the tidal pull tends to make fish more active.
- Photography and night observation: Astronomers and nature photographers plan shoots around new moon (darkest sky) or full moon (maximum moonlight).
- Calendar planning and festivals: Many religious and cultural events — Easter, Ramadan, Chinese New Year — are tied to the lunar calendar.
What are the most frequently asked questions about moon phases?
(FAQ is rendered from frontmatter as FAQPage schema.)
Which related tools are available?
- Unix Timestamp Converter — Convert dates and times to Unix timestamps, useful for querying databases around specific lunar events.
- Timezone Converter — Convert times between time zones, helpful when planning moon phase events across locations.
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