Moon Phase Calculator
The Moon's phase, age and illuminated fraction for any date, plus the next new and full moons — computed with Meeus's periodic series, accurate to about a minute.
Moon Phase Calculator: with the default inputs, phase is New Moon.
Local time on the 24-hour clock. The Moon's illumination changes by about 1% every three hours near the quarters.
0 for UTC, −5 for US Eastern Standard Time, +1 for Central European Time. Include daylight saving if it applies.
- Illuminated fraction
- 0.1%
- Age of the Moon (days)
- 29.14Days since the last new moon.
- Waxing or waning
- Waning — shrinking towards new
- Position in the cycle
- 99.1%
- Next new moon
- Friday 11 September 2026, 03:27
- Next full moon
- Saturday 26 September 2026, 16:49
- Last new moon
- Wednesday 12 August 2026, 17:37
- Lunation number
- 329Counted from the new moon of 6 January 2000, the epoch used by Meeus.
Assumptions
- Phase instants use Meeus, Astronomical Algorithms 2nd ed., chapter 49, including the 14 additional terms.
- The illuminated fraction uses the low-precision phase-angle series of chapter 48 (eq. 48.4).
- ΔT is treated as a constant 69 seconds, its approximate value in the 2020s.
- Phase names cover ±18 hours around the exact instant; first and last quarter are located from position in the lunation, not from their own series.
- Positions are geocentric; topocentric parallax is not applied.
| Phase | Local time (UTC+0) | Days away |
|---|---|---|
| New Moon | Friday 11 September 2026, 03:27 | 0.3 |
| Full Moon | Saturday 26 September 2026, 16:49 | 15.8 |
| New Moon | Saturday 10 October 2026, 15:50 | 29.8 |
| Full Moon | Monday 26 October 2026, 04:12 | 45.3 |
| New Moon | Monday 9 November 2026, 07:02 | 59.4 |
| Full Moon | Tuesday 24 November 2026, 14:54 | 74.7 |
| New Moon | Wednesday 9 December 2026, 00:52 | 89.2 |
| Full Moon | Thursday 24 December 2026, 01:28 | 104.2 |
How this is worked out
The formula
mean phase: JDE = 2451550.09766 + 29.530588861 k + 0.00015437 T² − 0.00000015 T³, T = k ÷ 1236.85 true phase = mean phase + 25 periodic corrections in M, M′, F and Ω + 14 small additional terms (Meeus ch. 49) age of the Moon = instant − preceding new moon phase angle i = 180° − D − 6.289 sin M′ + 2.100 sin M − 1.274 sin(2D − M′) − 0.658 sin 2D − 0.214 sin 2M′ − 0.110 sin D illuminated fraction k = (1 + cos i) ÷ 2
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Date
- A calendar date.defaults to today
- Hour of day
- Local time on the 24-hour clock. The Moon's illumination changes by about 1% every three hours near the quarters.from 0 to 23 · whole numbers only · defaults to 21
- Your offset from UTC
- 0 for UTC, −5 for US Eastern Standard Time, +1 for Central European Time. Include daylight saving if it applies.from -12 to 14 · defaults to 0
What you get back
- Phasemain answer
- Illuminated fraction
- Age of the Moon (days)
- Days since the last new moon.
- Waxing or waning
- Position in the cycle
- Next new moon
- Next full moon
- Last new moon
- Lunation number
- Counted from the new moon of 6 January 2000, the epoch used by Meeus.
What this assumes
- Phase instants use Meeus, Astronomical Algorithms 2nd ed., chapter 49, including the 14 additional terms.
- The illuminated fraction uses the low-precision phase-angle series of chapter 48 (eq. 48.4).
- ΔT is treated as a constant 69 seconds, its approximate value in the 2020s.
- Phase names cover ±18 hours around the exact instant; first and last quarter are located from position in the lunation, not from their own series.
- Positions are geocentric; topocentric parallax is not applied.
About this calculator
Give it a date and this returns the Moon's phase, how many days old it is, what fraction of the disc is lit, and when the next new and full moons fall — in your own local time.
How it is calculated
Two separate pieces of Jean Meeus's Astronomical Algorithms do the work.
The instants of new and full moon come from chapter 49. A mean phase is computed from the lunation number, then corrected by 25 periodic terms in the Sun's mean anomaly, the Moon's mean anomaly, the argument of latitude and the ascending node, plus 14 smaller additional terms. Those corrections matter: the Moon's orbit is elliptical and perturbed by the Sun, so a true new moon can fall more than half a day either side of the mean one. A naive "days since a known new moon, modulo 29.53" calculation — which is what most quick moon-phase code does — is wrong by up to about 14 hours.
The illuminated fraction comes from chapter 48, using the low-precision phase-angle series. Illumination is (1 + cos i) ÷ 2, where i is the Sun–Moon–Earth phase angle.
How accurate is it?
Compared against published phase times, the instants here land within about a minute through the present century, and the illuminated fraction is good to a few tenths of a percentage point. Two things limit it. First, the series is truncated — the full ELP theory has thousands of terms. Second, the results are naturally in Terrestrial Time and have to be shifted to Universal Time by ΔT, which is measured, not predicted; this calculator subtracts a constant 69 seconds, its value through the 2020s. Centuries away from now ΔT differs by minutes to hours, so distant dates carry a warning.
Times are displayed to the minute. Do not read anything into a difference of one or two minutes from another source; different tools truncate the series at different points and handle ΔT differently.
Reading the results
Age is measured from the true preceding new moon, not from a mean one, so it runs from 0 to roughly 29.3–29.8 days — real lunations vary in length by about 13 hours because of orbital eccentricity. Position in the cycle is that age as a percentage of this particular lunation.
The named phases cover a window of ±18 hours around each exact event, which is why a moon can read "Full Moon" for the better part of two days. The intermediate names — crescent and gibbous — cover the stretches in between. First and last quarter are located from the position in the cycle rather than from their own series, so they can sit an hour or two from the exact quarter; the new and full moon times in the table are the precise ones.
What the phase does not tell you
Phase says nothing about where the Moon is in your sky, whether it is up at all, or how large it looks. A full moon rises around sunset and sets around sunrise; a new moon is in the sky all day and invisible. And an eclipse needs more than the right phase: the Moon must also be near a node of its orbit, which is why solar eclipses happen at a handful of new moons rather than all of them.
Frequently asked questions
▸When is the next full moon?
The table lists the next eight new and full moons in your local time. Full moons fall about 29.53 days apart on average, but individual intervals vary by several hours.
▸How long is a lunar month?
The synodic month — new moon to new moon — averages 29 days 12 hours 44 minutes. Individual lunations run from about 29.27 to 29.83 days because the Moon's orbit is elliptical and perturbed by the Sun.
▸How accurate is this moon phase calculator?
The new and full moon instants land within about a minute of published values for dates in this century. The illuminated fraction is good to a few tenths of a percentage point. Dates centuries away are less certain because ΔT, the gap between Terrestrial Time and UT, is not precisely known.
▸What was the moon phase on my birthday?
Set the date to your birthday and the hour to the time of day. The phase, age and illuminated fraction are all computed for that exact moment.
▸Why is the moon full for two nights?
It is only exactly full for an instant, but the illuminated fraction stays above about 98% for more than a day either side, which the eye cannot distinguish. This calculator labels a ±18-hour window as full.
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