See the real Moon phase for any day of the month, with illumination percentage and the next New Moon and Full Moon computed in your browser.
This calendar computes the real position of the Sun and the Moon for local noon of each date shown, and converts the difference in ecliptic longitude between the two into a phase angle from 0 to 360 degrees (0 is New Moon, 180 is Full Moon). From that angle come the phase name (one of the 8 traditional buckets) and the illumination percentage, the fraction of the Moon's disc facing Earth that is lit by the Sun. The next Full Moon and New Moon are located with a lunar quarter search, the same kind of calculation used in professional astronomical ephemerides, so the date and time shown are precise, not an average of the 29.53-day cycle. Every calculation runs in your browser using the Astronomy Engine ephemeris library.
A complete lunar cycle, called a synodic month, lasts on average 29.53 days, the time between two consecutive New Moons. That period varies slightly from cycle to cycle (roughly between 29.18 and 29.93 days) because the Moon's orbit around Earth is elliptical rather than perfectly circular, so its orbital speed changes along the path.
By astronomical convention, that cycle is split into 8 named phases: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter and Waning Crescent. Each covers, on average, about 3.7 days of the cycle, except the four quarters (New, First Quarter, Full, Last Quarter), which mark an exact instant rather than a span.
The illumination percentage comes from the phase angle, the difference in ecliptic longitude between the Sun and the Moon as seen from Earth. When the angle is 0 degrees, the Sun and Moon sit in the same direction in the sky and the side of the Moon facing us is entirely in shadow (New Moon, 0 percent lit). When the angle reaches 180 degrees, the Moon sits opposite the Sun and we see the full disc lit (Full Moon, 100 percent).
The formula used is the standard illuminated fraction from positional astronomy: illumination = (1 minus the cosine of the phase angle) divided by 2. It yields 0 percent at New Moon, 50 percent at both quarters (90 and 270 degrees), and 100 percent at Full Moon, the same value observatories and nautical almanacs publish as the Moon's "illuminated fraction".
The best-established physical effect of the Moon's phase is on ocean tides: near New Moon and Full Moon, the Sun and Moon line up and their gravitational pulls add together, producing spring tides (higher highs and lower lows than usual). At the quarters, the Sun and Moon pull at different angles and neap tides are milder. Amateur astronomers also use the lunar calendar in practice: moonless skies near New Moon are the best for observing faint stars and doing astrophotography, while a Full Moon washes out the night sky.
Moon phases still organize cultural and religious calendars today, such as the Islamic calendar (Hijri, entirely lunar) and the traditional Chinese calendar (lunisolar, used to date Chinese New Year). The popular idea that the Full Moon affects sleep, mood or human behavior, on the other hand, has no consistent support in controlled scientific studies; it is old folklore, not a proven physical effect, unlike tides.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
<iframe
src="https://jkit.tools/embed/en-US/moon-phase-calendar"
width="100%"
height="600"
style="border:0"
loading="lazy"
title="Moon Phase Calendar"
></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
It's the Moon's visual shape at that moment (how much of the Sun-lit disc we can see from Earth), classified into one of 8 traditional names (New, Crescent, First Quarter, Gibbous, Full, and so on) based on the angle between the Sun and the Moon in the sky.
Use the arrow keys to move between days, Page Up or Page Down to change month.
The markers show the exact New Moon and Full Moon within the displayed month.
All Moon phase calculations run locally in your browser, no date is ever sent to a server.