astronomy · any past or future date
Moon Phase Calculator for Any Date
Calculate the exact phase angle, illumination, lunar age and Moon sign for any date and time. Then see the next four New, Full and quarter Moon moments in the timezone you entered.
What the numbers mean
Phase angle measures the Moon's apparent separation from the Sun along the ecliptic: 0° is New Moon, 90° first quarter, 180° Full Moon and 270° last quarter. Lunar age maps that angle onto the average 29.53-day synodic month. The real cycle varies slightly, so age is a useful phase measure rather than a stopwatch since the previous lunation.
This page owns any-date astronomical lookup. For the phase at your birth with a 30-part lunar-day interpretation, use Lunar Birthday.
How the moon phase is calculated
The calculator runs an open-source astronomy library in your browser. For the moment you enter it finds the Moon’s phase angle — how far the Moon has moved ahead of the Sun along the ecliptic — and the illuminated fraction of the disc, shown as a percentage. Lunar age is then derived from the angle:
age = angle ÷ 360 × 29.530588 days
Worked example: at a phase angle of 90° the age is 90 ÷ 360 × 29.53 ≈ 7.4 days, and roughly half of the visible disc is lit. At 180° the age is about 14.8 days — Full Moon. At 270°, about 22.1 days, the last quarter.
The same moment also gives the Moon’s zodiac sign and a search forward for the next four principal phases, shown in the time zone you entered.
Where one phase ends and the next begins
New, First Quarter, Full and Last Quarter are exact instants, but the calculator gives the four principal phases a narrow window around them so that the label stays useful:
- New Moon: below 11.25° or from 348.75°.
- Waxing crescent: 11.25°–78.75°.
- First quarter: 78.75°–101.25°.
- Waxing gibbous: 101.25°–168.75°.
- Full Moon: 168.75°–191.25°.
- Waning gibbous: 191.25°–258.75°.
- Last quarter: 258.75°–281.25°.
- Waning crescent: 281.25°–348.75°.
So “Full Moon” in the result means the Moon is within about a day of the exact Full Moon. For the exact minute, look at the list of next phases or the yearly Moon phases 2027 calendar.
Why the UTC offset matters
The Moon changes phase at a single worldwide moment, but that moment falls on different clock times — and sometimes different dates — around the globe. A Full Moon at 01:30 in Moscow is still the evening before in New York. Enter the local time and the offset that was in force at that place and date (remember summer time) and the calculator converts it correctly. If you only know the date, choose noon: the angle changes by about 12° a day, so noon keeps you within half a day of error.
Practical uses
- Photography and walks: check illumination before planning a night shoot or a moonlit walk; add moonrise and moonset times for your coordinates.
- Family history: look up the Moon on a wedding day or a grandparent’s birthday.
- Journaling: note the phase alongside mood or sleep entries and compare after a few months.
How to check the result against the sky
On a clear evening, enter the current date, time and offset and compare the illumination with what you see. Around 20–30% is a thin crescent, 50% a neat half, 90% and above an almost full disc. In the Northern Hemisphere a waxing Moon is lit on the right and a waning one on the left; south of the equator it is mirrored. If you cannot see the Moon at all, it may simply be below the horizon or too close to the Sun.
Frequently asked questions
Why can another calendar show another date?
One event is a single UTC moment, while local calendar dates depend on timezone. Different definitions can also matter for interpretive calendars such as void-of-course Moon.
Are the calendar meanings predictions?
No. Event times are astronomy; astrological meanings are optional cultural interpretation and cannot determine a personal outcome.
Why is the Moon not exactly 50% lit at first quarter?
Illumination depends on the true Sun–Moon–Earth geometry, while the phase angle is measured along the ecliptic, so the two differ slightly. At the quarter the lit fraction is very close to half.
How far back or forward can I calculate?
Any date the form accepts. The astronomy library is designed for centuries either side of today, which covers birthdays, anniversaries and future plans.
Why does lunar age not always match the days since the last New Moon?
Age here is the angle converted to an average 29.53-day month. Real lunations run a few hours shorter or longer, so the two can differ a little.