Though China has officially followed the Gregorian calendar since the rise of the Republic of China in 1912, many of the most important festivals (including Spring Festival, Mid-Autumn Festival, Qingming Festival, etc.) in the Chinese calendar are observed according to the lunar calendar, known as 农历 in Chinese. To this day, crops are planted by the lunar calendar in most places, and some Chinese people prefer to observe their birthdays according to the lunar calendar (you can calculate your lunar birthday here if you so desire).
The lunar year is made up of 12 months of 29 or 30 days, with extra “leap” months (闰月) added to about seven of every 19 years to keep it in time with the astronomical calendar. The earliest known written records of observation of the lunar calendar date back nearly 4,000 years to Shang Dynasty oracle bone carvings. Given its age, it is unsurprising that the system of marking time will contain a lot of 汉子 (hanzi, characters) you’ve never seen before, including the rarely-seen single character word for 20: 廿. If obscure characters are your thing, try checking out the Heavenly Stems and Earthly Branches.
Lastly, many of you may have heard that in China this year is 4711, a system which takes the reign of the mythical first emperor of China as its year 1. While some communities of overseas Chinese use this calendar year, none of the mainlanders surveyed in our unscientific poll had ever heard of this.