Chinese Lunar Calendar Explained

The Chinese lunar calendar is one of the oldest continuously used calendar systems in the world. It is technically a lunisolar calendar, meaning it tracks both the lunar cycle (the phases of the moon) and the solar year (the Earth's orbit around the sun). This dual tracking is the reason the Chinese calendar can stay synchronized with the seasons while still counting months by the moon.

Each lunar month begins on the day of the new moon and lasts until the next new moon arrives, a span of roughly 29.5 days. Because months cannot be half days long, actual months alternate between 29 and 30 days. A standard lunar year is made up of 12 of these months, adding up to about 354 days. Since this falls 11 days short of a 365-day solar year, the Chinese calendar inserts a leap month every few years to catch up.

The lunar calendar has been used in China for thousands of years, and it still governs traditional holidays such as Chinese New Year, the Mid-Autumn Festival, and the Dragon Boat Festival. It also plays a central role in folklore traditions such as the Chinese Gender Calendar, which you can try in our free calculator.

Lunar months are numbered 1 through 12. Month 1, also called Zhengyue, starts on Chinese New Year and typically falls in late January or February of the Gregorian calendar. Because Chinese New Year moves around within the Gregorian calendar, a specific Gregorian date can correspond to different lunar months in different years.

For example, a conception on March 15 might fall in lunar month 2 in one year and lunar month 1 in another, depending on where the new moons fell that particular year. This is why it is not possible to map Gregorian months one-to-one onto lunar months. A proper conversion requires looking up the lunar calendar for the specific year in question.

Because 12 lunar months add up to about 354 days, the lunar year is 11 days shorter than the 365-day solar year. Without correction, the lunar calendar would drift out of sync with the seasons within a few years: Chinese New Year would gradually migrate into the summer, and the traditional agricultural rhythm would collapse.

To prevent this drift, the Chinese calendar uses a system of leap months. On average, a leap month is inserted roughly every 2 to 3 years — more precisely, 7 times in every 19-year cycle. When a leap month is added, the year contains 13 months instead of 12, which brings the calendar back into alignment with the solar year.

Leap months are always labeled with the same number as the preceding regular month. For example, a leap month following lunar month 4 is itself called leap month 4 (rather than month 5). This convention has a direct implication for the Chinese Gender Calendar: conceptions that occur during a leap month are traditionally assigned to the preceding regular month when looking up the chart.

Traditional Chinese age counting differs from Western age counting in two important ways. First, babies are considered 1 year old at birth — the time in the womb is counted toward the first year of life. Second, everyone gains a year at Chinese New Year rather than on their individual birthday. The combination of these two rules means that lunar age is usually 1 to 2 years higher than Western age.

The exact difference depends on whether your birthday falls before or after Chinese New Year in a given year. Consider two mothers both born in 1995, one on January 10 and the other on May 15. On May 1, 2026, just before Chinese New Year has happened for their birthdays that year:

• January 10, 1995 birthday: Already past Chinese New Year 1995, so she has experienced roughly 31 lunar new years since birth. Lunar age = 32.
• May 15, 1995 birthday: Born after Chinese New Year 1995, so she has experienced roughly 31 lunar new years since birth. Lunar age = 32.

The difference emerges near the boundary. A mother born in late January 1995 might be lunar age 33 in early 2026, while another born in late February 1995 might still be lunar age 32. These edge cases are exactly why a calculator is so useful. You can try our standalone lunar age calculator to verify your own lunar age.

The Chinese Gender Calendar uses two lunar-based inputs: the mother's lunar age and the lunar month of conception. Both come directly from the lunar calendar system described above. Without a correct lunar conversion, the chart cannot be read accurately. This is why every step — lunar age, lunar month, leap month handling — matters for anyone who wants to use the chart seriously.

For a full walkthrough of how those inputs feed into the chart, see our guide on how the Chinese Gender Calendar works. For the historical origins of the calendar itself, read our history of the Chinese Gender Calendar guide.

It is worth remembering that the Chinese Gender Calendar is traditional folklore with no scientific basis. Reading the lunar calendar correctly gets you to the right folklore answer, but that answer has about the same accuracy as a coin flip. For the research, see our accuracy guide.

Because the lunar calendar works so differently from the Gregorian calendar, Western parents often run into the same handful of misunderstandings. The most common ones are worth calling out.

• Mapping Gregorian months to lunar months. January is not lunar month 1, February is not lunar month 2, and so on. The lunar calendar starts each year at Chinese New Year, which typically falls in late January or February.
• Assuming your birthday gives you a birthday. In the traditional Chinese system, your age increases at Chinese New Year, not on your individual birthday. Westerners who insist on using their birthday as the age transition point will get the wrong lunar age.
• Ignoring leap months entirely. Some online converters simply skip leap months. This is incorrect and will shift the lunar month in years that contain them.
• Mixing up lunar year and solar year. A lunar year is about 354 days long, while a solar year is about 365.25 days. Any calculation that treats them as interchangeable will accumulate error.
• Thinking there is one fixed Chinese New Year date. Chinese New Year falls on a different Gregorian date every year, typically between January 21 and February 20.