Moon Phase Calculator

Written byOleh Soloninupdated 25 September 2026

Date

Result

Phasewaning crescent
Illuminated, %18.4
Age, days25.36
Directionthe moon is waning
Next new moonOctober 10, 2026 at 15:50 UTC
Next full moonOctober 26, 2026 at 04:11 UTC
Accuracy
The moments of new and full moon follow Jean Meeus's algorithm and agree with NASA's tables to within a couple of minutes. The age and the illumination are given for noon UTC on the chosen date.

Twenty-nine and a half days, on average

Shows the phase of the moon on any date with its age in days, the illuminated fraction and the next new and full moons.

The moon returns to the same phase every 29.53 days — the synodic month. Counting from a known new moon gives the age of the moon on any date, and from the age the illuminated fraction follows directly.

The word on average is doing real work there. The moon's orbit is elliptical, and a real month can run half a day shorter or longer than the mean. So the calculator does not step through mean months; it works out the true moments of the phases with Jean Meeus's algorithm, which agree with NASA's tables to within a couple of minutes.

How to use

Open the page: the date field already holds today's date, so tonight's phase is on screen straight away.
For another night — a trip, a shoot, a birthday — pick that date in the field.
Read the percentage lit and the age rather than the name. A phase name covers a stretch of the month; the percentage moves every hour.
Use the dates of the next new and full moons to plan the darkest skies for stars and the brightest night for a moonlit landscape.

Eight phases, and why a quarter is half lit

The month starts at new moon, when the moon sits roughly between the earth and the sun and shows us its dark side. A day or two later a thin waxing crescent appears in the evening sky. First quarter comes on average at about 7.4 days — in some months well before or after, 6.8 in June 2026 — when exactly half the disc is lit — the quarter is a quarter of the way round the orbit, not a quarter of the face. Then comes the waxing gibbous moon, full moon at about 14.8 days on average, and the same sequence in reverse: waning gibbous, last quarter at about 22.1 days on average and a waning crescent before the next new moon.

The four principal phases — new, first quarter, full and last quarter — are moments rather than stretches of time. The calculator gives a date the name of a principal phase when the exact moment is less than half a day away; everything in between is a crescent or a gibbous moon. First quarter in June 2026 falls on the 21st at 21:55 UTC, so 21 June, 40 percent lit, is named first quarter, while 20 June, at 30 percent, is still a waxing crescent.

How the age and the illumination are worked out

First come the true moments of the new moons around the chosen date. The mean synodic month of 29.530589 days gives only an approximate time; Meeus's algorithm (Astronomical Algorithms, chapter 49) adds corrections for the elliptical orbits of the moon and the earth. The largest reaches 0.4 of a day, which is why an uncorrected new moon easily slips onto the neighbouring date.

The age of the moon is the time from that true new moon to noon UTC on the chosen date. The illuminated fraction follows from how much of the month has passed: fraction = (1 − cos(2π × age / length of the month)) / 2. The June 2026 lunation lasts 29.28 days; on 21 June the age is 6.38 days, giving (1 − cos(1.369)) / 2 ≈ 0.40, or 40 percent.

The illumination formula is an approximation: the true fraction depends on the angle between the sun and the moon, which does not grow evenly. The error is a few percent, invisible to the eye. The moments of the phases are more precise: across all 50 principal phases of 2026 they sit within two minutes of NASA's table.

Where and when to look for the moon

A waxing crescent shows low in the west soon after sunset and sets not long after the sun. First quarter rises around midday and is up for the first half of the night. A full moon rises around sunset and stays up all night. Last quarter rises around midnight and lingers into the morning, and a waning crescent is seen in the east before dawn.

In the northern hemisphere a waxing moon is lit on its right-hand edge and a waning one on the left. For stars and the Milky Way the best nights are the few around new moon; for a landscape lit by the moon, the days around full moon, when it rides high and the light is even.

Full and new moons in 2026

Exact moments from NASA's astronomical tables, in Universal Time. Each full moon arrives about a day earlier in the month than the last one, because a lunar month is shorter than a calendar month — which is why 2026 has thirteen of them, with two in May.

Source: NASA GSFC, Phases of the Moon 2026–2030, Universal Time. Checked 14 September 2026.
Month	New moon, UTC	Full moon, UTC
January	18 Jan, 19:52	3 Jan, 10:03
February	17 Feb, 12:01	1 Feb, 22:09
March	19 Mar, 01:23	3 Mar, 11:38
April	17 Apr, 11:52	2 Apr, 02:12
May	16 May, 20:01	1 May, 17:23 and 31 May, 08:45
June	15 Jun, 02:54	29 Jun, 23:57
July	14 Jul, 09:43	29 Jul, 14:36
August	12 Aug, 17:37	28 Aug, 04:18
September	11 Sep, 03:27	26 Sep, 16:49
October	10 Oct, 15:50	26 Oct, 04:12
November	9 Nov, 07:02	24 Nov, 14:53
December	9 Dec, 00:52	24 Dec, 01:28

What this calculator shows

The phase, its name and whether the moon is waxing or waning
The age of the moon in days and the percentage lit
The dates of the next new and full moons

What to keep in mind

The moments of the phases follow Jean Meeus's algorithm without the small planetary terms and agree with NASA's tables to within two minutes. The age and the illumination are for noon UTC on the chosen date.
The illuminated fraction is a geometric figure; the moon looks brighter than the percentage suggests because the eye responds to light logarithmically.

FAQs

How can I tell waxing from waning?

In the northern hemisphere a waxing moon is lit on the right. In the southern hemisphere it is the other way round, which is worth remembering before trusting a mnemonic from the other side of the world.

How long is a lunar month?

29 days 12 hours 44 minutes on average. The sidereal month, the time to return to the same star, is shorter — 27.3 days — because the earth has moved along its own orbit meanwhile.

Why does another site give a different time?

Usually because of the time zone: this page gives UTC, and many almanacs give local time, which near midnight changes even the date. Sites that step through mean months are also hours out. Here the moments follow Meeus's algorithm and sit within two minutes of NASA.

Why is a half-lit moon not half as bright?

Because the terminator falls on rough ground casting long shadows, and because the surface reflects most strongly straight back. A full moon is roughly ten times brighter than a half moon, not twice.

Why does 2026 have thirteen full moons?

A lunar month is almost a day shorter than a calendar month, and over a year that adds up to about eleven days. When a full moon falls in the first days of a month, the next one fits into the same month — in 2026 that happens in May, on the 1st and the 31st.

What phase is the moon in today?

The calculator above shows it: the date field opens on your device's date. The phase changes smoothly, so for precision look at the percentage lit, which rises or falls by several points a day.

Worked example

The solstice

Input: 21 June 2026

Output: first quarter, 6.4 days old, 40 percent lit

Note: The exact moment of first quarter is 21:55 UTC on 21 June. At noon UTC it is ten hours away, so the date takes the quarter's name.

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