The only thing anyone knows about the Chinese calendar is that they don't have the foggiest idea of how it works. We're here to change that once and for all.

The Chinese calendar is a combination of two calendars--the solar and the lunar--and is thus classified as "lunisolar" by people who know too much for their own good...which will soon include you!

The Solar Calendar

The solar calendar, also called the farmer's calendar, is made up of 24 roughly two-week-long segments called "solar terms." These are basically season markers, though Chinese seasons overlap only half-way with the Gregorian calendar's--the internationally used calendar. For example, summer starts around May 6th according to the solar calendar, and around June 21st according to the Gregorian calendar. Conceptual differences follow:

Chinese: it's 70 degrees, summer's starting!

American: my face just melted off, summer must be starting!

Despite the differences, the solar calendar is pretty close to the Gregorian one as it's still ~365 days long. However, the first day of the solar calendar year is the December solstice--the shortest day of the year in the Northern hemisphere--usually December 21st or 22nd.

The Lunar Calendar

The Chinese lunar calendar, otherwise known as the "does anyone have the slightest clue how it works?" calendar, works like this:

1. 1. A new day starts at midnight.
2. A new month starts on the day of the new moon (no moon visible). The specific time of day when the new moon occurs--yes, the moon doesn't wait for night to fall to go change phases--determines the length of a month. More details in Lunar Math »
3. There's 12 months in a regular year, for a total of ~355 days, and since 355 obviously doesn't equal 365...
4. ...every few years, freak out because you're way ahead of schedule, and throw in a leap month (an extra month) to pace yourself. The lunar calendar is obviously a death sentence for pregnant women. More details about how the leap months work in May's Over, Time For 2nd May »

Lunar Math

Let's say there are 29.5 days between two new moons.^* Here are two examples illustrating how the start time and length of months may vary:

Scenario 1

1st new moon: April 1st, 1am

2nd new moon: April 1st, 1am + 29.5 days = April 30th, 1pm.

Result: the first day of the next month is said to be April 30th.

Scenario 2

1st new moon: April 1st, 1pm

2nd new moon: April 1st, 1pm + 29.5 days = May 1st, 1am.

Result: the first day of the next month is said to be May 1st.

Thus, months on the Chinese calendar vary from 29 to 30 days long, and the same month may be 29 days long one year and 30 days long the next.

May's Over, Time For 2nd May

The leap months come from adjusting the lunar calendar to the solar calendar, which is why it was a bad idea to skip the solar calendar section.

The 24 solar terms in the solar calendar add up to ~365 days, while the 12 lunar months add up to ~355. The one to compromise is the lunar calendar. Good thing too, because otherwise we'd have lunar Julys in the middle of winter every so often. This is how it's adjusted:

First we divide the 24 solar terms into 12 pairs:

(1st, 2nd), (3rd, 4th), ..., (23rd, 24th)

Think of these as solar months.

The point in the middle of each pair, at the midpoint of the month, is called a Solar Center Point...because that's what people who invented this whole business thought would be most confusing. So there's a Solar Center Point between solar terms 1 & 2, one between 3 & 4, etc.

Since the lunar months are shorter on average than solar months, each lunar month has a Solar Center Point at a later date than the month before, until every few years, you run into a lunar month that doesn't have a Solar Center Point at all. That month is made the leap month. Let's confuse ourselves further with an illustration:

This chart superimposes the lunar and solar calendars and gives us our first peek at the "Chinese calendar." On the left you have the solar terms, 24 per year, roughly two weeks long each. There's a Solar Center Point marker between every other set of solar terms. On the right you have lunar months, roughly 29.5 days long each.

See how the leap month doesn't have a Solar Center Point inside it?

Ok, so we found the leap month, but isn't it supposed to be an extra month, not just one of the regular months? You're right, the lunar leap year has 13 months, not 12.

To make things as confusing as possible, the leap month takes on the same name as the previous month. For example, let's say the month that was supposed to be June has no Solar Center Point. Then it is called May instead, and the regular June comes after that. The resulting month order is this:

..., April, May, May again (leap month), June, July,...

There are two Mays! One is the regular lunar May, and one is leap May. This lunar leap year then has ~385 days.

What Just Happened?

In case you missed it, we just took the solar and lunar calendars, mixed them together and cooked up the Chinese calendar, which observes both the 24 solar terms and the lunar months with their nutty leap month business.

Three Calendars?

The Chinese calendar has given way to the Gregorian calendar for managing daily affairs, as the latter is much more practical. If you're scheduling a business meeting, you don't leave it for the moon to decide the day. Eggs don't expire later just because the moon's period is irregular. However, the Chinese calendar it's still used for marking seasons and holidays. A few seasonal holidays are managed by the solar calendar, while birthdays and most cultural holidays--like Chinese New Year--are celebrated according to the lunar calendar. This means that Chinese people celebrate their birthday on a different day (according to the Gregorian calendar) every year, to the great confusion of foreigners. Sometimes I think they do it just to mess with us. If that's the case, we deserve it, because the American system of measurement--feet, miles, ounces--is a far meaner practical joke.

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