Lunar vs. Gregorian Calendar: When Do We Use Each?

Next week, one of the most important Chinese holidays is here: National Day (国庆节, Guóqìng Jié). Even though National Day falls on October 1st, it is a week-long holiday (it’s also called Golden Week, 黄金周, huángjīn zhōu), making it one of the longest holidays of the year. During this time, many people (including me whenever I can) often go home to spend the holiday with their loved ones or go travelling.

This year is especially special because another festival also falls during this week: the Mid-Autumn Festival (中秋节, Zhōngqiū Jié). You might wonder why it doesn’t always line up with Golden Week. The reason is that National Day is always on October 1st according to the Gregorian (Roman) calendar (公历, gōnglì), while the Mid-Autumn Festival follows the lunar calendar (农历, nónglì), which works a little differently. That’s why the Moon Festival (which is another name for the Mid-Autumn Festival) falls on a different date each year according to the Gregorian calendar.

When do we use which calendar?

Let’s take a look at these two calendars and why we use each. The Gregorian calendar is used for most everyday purposes in China, like work and school; while the lunar calendar is used mainly for traditional festivals, like the Dragon Boat Festival, Mid-Autumn Festival and Spring Festival. For western holidays (Halloween, Christmas, New Year’s Eve) we refer to the Gregorian calendar.

But what about birthdays? Here it gets a little tricky. Many Chinese families celebrate their birthdays according to the Gregorian calendar. Our birthdays on official documents, IDs, and passports are all based on the Gregorian calendar as well.

However, some more traditional families (especially in rural areas) might prefer to celebrate birthdays according to the lunar calendar. For example, my parents always wish me a happy birthday on my lunar birthday, and never on my Gregorian birthday.

There are also probably quite a few Chinese people who celebrate both birthdays, so in the end, it really comes down to personal preference.

What is the Lunar Calendar?

The lunar calendar is based on the moon, not the sun. Each month begins with the new moon and ends with the next one. Because a lunar month is about 29.5 days, months are usually either 29 or 30 days long.

A full lunar year has 12 months, which adds up to about 354 days, roughly 11 days shorter than a solar year. Because of this difference, lunar dates shift each year compared to the Gregorian calendar. That’s why festivals like Chinese New Year and the Mid-Autumn Festival fall on different dates every year.

To keep the lunar calendar roughly in line with the solar year, sometimes a leap month (闰月, rùnyuè) is added. A leap month is an extra month inserted about every 2–3 years, which prevents festivals from drifting too far into different seasons. Thanks to this, the Mid-Autumn Festival always stays in the fall, and Chinese New Year always falls in winter or early spring.

If you want to check which day on the lunar calendar matches a date on the Gregorian calendar (or vice versa), you can do it at the Hong Kong Observatory’s website.