Moon phase for any date and time: the phase name, percentage illuminated and moon age in days, with the dates of the next new and full moons.
At 21:00 on Sun 27 Sep 2026, UTC time, the Moon's phase is waning gibbous, 98% lit and 16.7 days past new. The next full moon is Mon 26 Oct 2026 04:11 (UTC+00:00) and the next new moon Sat 10 Oct 2026 15:50 (UTC+00:00).
New moon at Fri 11 Sep 2026 03:26 (UTC+00:00), so the Moon is 16.73 days old.
Meeus ch. 49 series with all periodic and planetary terms; ΔT = TT − UT taken as 69 s. All 50 USNO phase times for 2026 are matched within 0.8 minutes.
Meeus eq. 48.4 (low-precision phase angle). The idealised curve in the chart ignores the Moon's elliptical orbit.
The Moon's phase follows from two things: the time since the last true new moon (its age) and the phase angle between the Sun and Earth as seen from the Moon, which sets the lit fraction k = (1 + cos i)/2. New, quarter and full moon instants come from Jean Meeus's lunar series, which reproduce all 50 US Naval Observatory phase times for 2026 to within 0.8 minutes.
Observers, photographers and anglers use it to plan around dark skies or a full moon. At 12:00 UT on 15 January 2026 the Moon was a waning crescent, 10% lit and 26.43 days old, with the next new moon 3.33 days away.
A phase name covers 12 hours either side of the exact instant, so a calendar that labels whole days can differ by one day. Times are shown in the zone you pick, and the Southern Hemisphere option mirrors which side of the disk is lit.
Checked against: USNO API: full moon 2026-03-03 11:38 UT, 100% illuminated at noon; previous new moon 2026-02-17 12:01 UT → age 13.999 days (Python datetime)
Checked against: USNO API: 10% illuminated at 12:00 UT; new moons 2025-12-20 01:43 and 2026-01-18 19:52 UT, full moon 2026-02-01 22:09 UT (differences by Python datetime)
Checked against: USNO API: new moon 2026-08-12 17:37 UT, 0% illuminated; previous new moon 2026-07-14 09:43 UT → age 29.095 days
Checked against: USNO API: first quarter 2026-01-26 04:47 UT (7.2 h earlier), 54% illuminated at noon; new moon 2026-01-18 19:52 UT → age 7.672 days
The mean synodic month, from one new moon to the next, is 29.530589 days, about 29 days 12 hours 44 minutes. Single lunations vary because the Moon's orbit is elliptical: the same Meeus series used here gives lengths between 29.27 and 29.83 days for every lunation from 1900 to 2100.
The full moon is a single instant, so its calendar date depends on the time zone. The full moon of December 2026 is at 01:28 UT on 24 December (USNO), which is still 23 December at 20:28 in New York. Enter your own time zone to see the date and time that apply where you are.
The common definition is the second full moon in one calendar month, which happens because the 29.5-day lunar cycle is shorter than most months. 31 May 2026 was one: USNO lists full moons at 17:23 UT on 1 May and 08:45 UT on 31 May. The older almanac definition is the third of four full moons in an astronomical season.
It is waxing from new moon to full moon, when the lit fraction grows each night, and waning from full back to new. Each half lasts about 14.8 days on average. In the Northern Hemisphere a waxing moon is lit on the right; south of the equator the picture is mirrored, so it is lit on the left.
About 50%. The name refers to the Moon having travelled a quarter of its orbit since new moon, not to the lit area. The lit fraction passes 50% within hours of first and last quarter: at 12:00 UT on 26 January 2026, 7.2 hours after first quarter, it was 54% (USNO).
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 5 worked examples whose answers come from independent sources; for example, “Full moon of the 3 March 2026 lunar eclipse” is checked against USNO API: full moon 2026-03-03 11:38 UT, 100% illuminated at noon; previous new moon 2026-02-17 12:01 UT → age 13.999 days (Python datetime).
J. Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 48 (illuminated fraction) and ch. 49 (phases of the Moon); US Naval Observatory — Phases of the Moon (cross-check).
5 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
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