Moon Phase Calculator: Illumination and Esoteric Rituals

Determine the approximate lunar phase, illumination percentage, and optimal manifestation rituals for any calendar date.

Working out the Moon's phase and illumination: the method

The tool measures the Moon's age in days since a reference new moon (11 January 2024 at 11:57 UT), modulo the mean lunation of 29.53058867 days, then derives the illumination as (1 − cos(2π × age / 29.53)) / 2 and one of eight phases. It is a mean model: compared with US Naval Observatory ephemerides, the phase name shown can be up to a day off.

Calculation

The chosen date is read at noon, local time on your device. The Moon's age is the gap from the 11/01/2024 new moon (11:57 UT), folded into a 29.53058867-day cycle. Phases are assigned by age bands centred on the principal phases (± 0.92 days): new moon from 28.61 to 0.92 days, waxing crescent to 6.46, first quarter to 8.30, waxing gibbous to 13.84, full moon to 15.69, waning gibbous to 21.23, last quarter to 23.07, then waning crescent.

Checked example: the US Naval Observatory gives the full moon on 26 October 2026 at 04:12 UT. For 26/10/2026 (Paris time) the tool computes an age of 14.9 days and 100% illumination, and shows Full Moon. The new moon of 10 October 2026 (15:50 UT), however, is shown that day as a 1% waning crescent: for this lunation the mean model runs almost a day late, and New Moon appears on the 11th.

Limits

  • The real lunation varies by several hours around its mean because the Moon's orbit is elliptical; a mean model does not follow this.
  • Near a band boundary, the name shown can switch a day early or late; the illumination percentage is more reliable than the name.
  • The calculation is made at local noon: it ignores the observing time, and the name shown can differ by a day between distant time zones. For a precise observing date, use an official ephemeris.
  • The ritual suggestions for each phase come from esoteric practice and have no demonstrated effect.

Sources and dates: US Naval Observatory, Dates of Primary Phases of the Moon: new moon of 11/01/2024 at 11:57 UT, October 2026 phases (checked 14/10/2026).

Frequently Asked Questions

How many days is a lunar cycle?

A lunation, from one new moon to the next, lasts 29.53 days on average, about 29 days 12 h 44 min. The actual length varies by several hours from one cycle to the next; the tool uses the mean value of 29.53058867 days.

When is the next full moon?

According to the US Naval Observatory, the late-2026 full moons fall on 26 October at 04:12 UT and 24 November at 14:53 UT. The tool shows Full Moon on both days; for other lunations its mean model can shift the name by a day, and an illumination close to 100% remains the best guide.

How is the Moon's illumination percentage calculated?

The tool applies (1 − cos(2π × age / 29.53)) / 2: 0% at new moon, 50% at the quarters, 100% at full moon. On day 14 of the cycle the result is about 99 to 100%.

Why does the phase shown differ from a lunar calendar?

The tool starts from a reference new moon and a mean cycle length without correcting for the Moon's elliptical orbit. The name shown can therefore be up to a day off an official ephemeris.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.