What Is a Lunar Calendar?
A lunar calendar is a calendar whose months follow the phases of the Moon. Each month begins at the new moon, or at the first sliver of the crescent seen after it, and runs 29 or 30 days, the length of one cycle of phases. Twelve such months make a lunar year of about 354 days, 11 days shorter than the solar year of the seasons. That gap is the whole story of lunar calendars: some ignore it, some patch it with an extra month every few years, and the Gregorian calendar most of the world uses day to day solved it by abandoning the Moon altogether.
This site uses the term in a second, everyday sense: a calendar of the Moon’s phases laid over ordinary dates, telling you what the Moon is doing on any given day. The lunar calendar for today is that kind. The guide below covers both meanings, starting with the cycle they are built on.
The lunar month
The cycle from one new moon to the next is the synodic month. It averages 29 days, 12 hours, and 44 minutes, or 29.53 days, but no single cycle is exactly that long: because the Moon’s orbit is an ellipse, and Earth’s orbit around the Sun is one too, individual months run from about 29.3 to 29.8 days. A calendar cannot have a month of 29 and a half days, so lunar calendars alternate months of 29 and 30 days and correct the count now and then by observation or by rule.
Two other lunar months matter for the pages on this site. The sidereal month, 27.3 days, is the time the Moon takes to return to the same position against the stars; it is why the Moon’s zodiac sign cycles faster than its phases. The anomalistic month, 27.55 days, is the time between two perigees, the Moon’s closest points to Earth; it runs on its own schedule, independent of the phases, which is why a full moon falls near perigee only now and then and makes a supermoon.
The lunar year and the 11-day gap
Twelve lunar months add up to 354.37 days. The year of the seasons, from one March equinox to the next, is 365.24 days. A calendar that keeps strictly to the Moon therefore starts each new year about 11 days earlier against the seasons than the year before, and after about 33 years it has cycled all the way around. The Islamic calendar works exactly this way, and Ramadan moves through winter, autumn, summer, and spring in turn.
The same arithmetic produces the 13-moon year. A solar year holds 12.37 lunar cycles, so roughly every two to three years a calendar year contains 13 full moons instead of 12. The extra one is the Blue Moon of the modern definition. Calendars that want to stay with the seasons use that thirteenth moon as a leap month.
Lunar, solar, and lunisolar calendars
Three families of calendars answer the 11-day problem differently.
Purely lunar calendars follow the Moon and let the seasons drift. The Islamic (Hijri) calendar is the main living example: 12 months of 29 or 30 days, a year of 354 or 355 days, each month traditionally beginning when the new crescent is first sighted after sunset.
Solar calendars follow the Sun and ignore the Moon. The Gregorian calendar still has months, a word derived from “moon,” but they are fixed blocks of 28 to 31 days with no connection to the phases; a full moon can fall on any date. The Persian calendar and the Coptic and Ethiopian calendars are solar too.
Lunisolar calendars keep lunar months and insert a thirteenth month, a leap month, whenever the count falls too far behind the Sun. The Chinese, Hebrew, Hindu, Buddhist, and traditional Korean, Vietnamese, and Tibetan calendars all work this way. The arithmetic behind most of them is the Metonic cycle, named for the Athenian astronomer Meton: 19 solar years are almost exactly 235 lunar months, so adding seven leap months in every 19 years keeps the calendar aligned to within a few hours per cycle. The Hebrew calendar adds its leap month in fixed years of the cycle; the Chinese calendar derives its leap months from the Sun’s position, with the same average of seven in 19.
The Chinese lunar calendar
The Chinese calendar is the lunisolar calendar most English speakers meet, through Lunar New Year and the Mid-Autumn Festival. Its months begin at the new moon, computed for Beijing time (UTC+8), which is why the Chinese date of a new moon can differ by a day from the UTC date on this site. The year begins at the new moon that falls between January 21 and February 20: 2026 is the Year of the Horse, beginning February 17, 2026, and 2027, the Year of the Goat, begins February 6, 2027. The Chinese year 2025 had a leap month and 13 new moons; 2026 is a common year of 12.
Because the months follow the Moon, the big festivals fall on fixed phases. The Mid-Autumn Festival is the 15th day of the eighth month, at or near the full moon of September or early October; the Lantern Festival is the first full moon of the year. The Chinese date for any day, and the lunar date of other calendars, is a conversion rather than an observation, and it is not yet part of this site.
Where the Moon still sets dates
Even the solar Gregorian calendar carries the Moon inside it. Easter is the first Sunday after the first full moon on or after March 21, computed by a church rule that follows the real Moon closely but not exactly; in 2027 Western churches celebrate it on March 28 and Orthodox churches, which apply the rule to the Julian calendar, on May 2. Passover begins at the full moon of the first spring month of the Hebrew calendar, Ramadan starts with the crescent of the ninth Hijri month, and Diwali is lit at the new moon of the Hindu month of Kartika, in October or November. The dates move against the Gregorian calendar because they are keeping time with the Moon.
Lunar days and today’s lunar date
Inside a lunar month, days are counted from the new moon. On this site that count is the lunar day: day 1 begins at the new moon and a cycle has 29 or 30 days, the full moon arriving around day 15. The Hindu calendar counts the same stretch in 30 tithis, each the time the Moon takes to pull another 12 degrees ahead of the Sun rather than a fixed 24 hours, so a tithi can be shorter or longer than a day. When someone asks for the lunar date today, both the cycle day on the daily page and the Chinese or Hindu calendar date are honest answers, depending on which calendar they mean.
The calendar of phases on this site
The lunar calendar you find here keeps Gregorian dates and adds the Moon: the phase and how much of the disk is lit, the sign the Moon is in, the day of the cycle, the distance from Earth, and the next full moon and new moon. On top of that sit the traditions that have followed the Moon’s rhythm for centuries, planting by the moon and the lunar hair calendar, presented as traditions. All times are in UTC with your local time next to them; the methodology page explains the calculations.
Frequently asked questions
What is the lunar calendar today?
Today’s lunar calendar is the Moon’s current phase, its sign, and the day of the cycle counted from the last new moon; the homepage shows all three for today, with times in UTC and your local time beside them. In the Chinese and other lunisolar calendars, today’s lunar date is a month and day in a calendar whose months begin at the new moon, and it needs a conversion table rather than a glance at the sky.
What are 13 lunar months?
A solar year holds 12.37 lunar months, so about every two to three years a year contains 13 full moons, or 13 new moons, rather than 12. Lunisolar calendars turn the extra moon into a leap month, seven times in every 19 years, to keep the months in step with the seasons. The phrase also names proposals for a calendar of 13 fixed months of 28 days, such as the International Fixed Calendar, which follow neither the Moon nor the old months.
What is the Chinese Lunar Calendar for 2026?
In the Chinese calendar, 2026 is the Year of the Horse. It begins at the new moon of February 17, 2026, and runs until February 5, 2027; the Year of the Goat follows on February 6, 2027. It is a common year of 12 lunar months, after a 2025 that carried a leap month. The months begin at the new moon as computed for Beijing time, and festival dates follow the phases: the Mid-Autumn Festival on the full moon of the eighth month, the Lantern Festival on the first full moon of the year.
How many lunar months in a year?
Twelve and a fraction: 12.37 lunar months of 29.53 days fit into one solar year of 365.24 days. Twelve lunar months make 354 days, 11 days short of the year, which is why a purely lunar calendar drifts through the seasons and a lunisolar calendar adds a thirteenth month seven times every 19 years. Counted by full moons, most years have 12 and some have 13.