Calculate the Moon Phase

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 follows the astronomical standard equations from Jean Meeus, Astronomical Algorithms — accurate to within a few minutes for full moon and new moon events. No location required, no server upload — everything runs directly in your browser.

How is the moon phase calculated?

Astronomical standard method: The calculation follows the equations from Jean Meeus, Astronomical Algorithms (chapters 47–48). This is the same method used by planetarium software and astronomical almanacs — far more precise than the simple “synodic month of 29.53 days” approximation used by many online calculators.

Three astronomical inputs:

JDE = Julian ephemeris date (selected date)
M   = mean anomaly of the sun
M'  = mean anomaly of the moon
F   = moon's argument of latitude

Phase precision: To each mean-phase time, periodic corrections are added (Eq. 47.2 for full moon and new moon, Eq. 47.3/47.4 for the quarter phases). These corrections account for solar and lunar eccentricity, gravitational perturbations, and planetary influences.

Illumination:

Illumination = (1 − cos i) / 2

i = phase angle between Sun, Earth, and Moon. Yields 0 at new moon (0% lit) and 1 at full moon (100% lit).

The result is accurate within a few minutes — far more precise than the simple synodic-month approximation.

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.