The Chinese Calendar

Introduction to the Chinese Calendar

3,000+ Years of Timekeeping

One of the most sophisticated calendar systems in human history

The Chinese calendar is a lunisolar system tracking both moon phases and the sun's position. It incorporates lunar months while using solar markers to stay aligned with the seasons.

Historical Origins

Yellow River Civilisation and the Calendar's Birthplace

The Yellow River — Cradle of Chinese Timekeeping

The calendar's structure is embedded in the climate and agriculture of the Central Plains

The Chinese lunisolar calendar is a product of the Yellow River (黃河 Huánghé) Central Plains (中原 Zhōngyuán) millet-farming civilisation. The 24 Solar Terms are calibrated to this temperate monsoon climate (34–38°N latitude) — terms like 大雪 Dàxuě (Major Snow) and 霜降 Shuāngjiàng (Frost Descent) describe phenomena that only exist in northern temperate regions.

Evolution of the Calendar: From Oracle Bones to the Shoushi System

The Chinese calendar was not invented once and frozen in time. Over more than three millennia, successive dynasties commissioned astronomers to reform the calendar — correcting accumulated errors, incorporating new observations, and refining computational methods. Over 100 official calendars were promulgated across Chinese history. Each reform represented the state of astronomical knowledge of its era, and the right to promulgate the calendar was an imperial prerogative symbolising the mandate to order time itself.

The Legendary Origins and the Xia Almanac

司馬遷 Sīmā Qiān’s Shiji (史記, Records of the Grand Historian, c. 94 BCE) attributes the establishment of the calendar to the 黃帝 Huángdì (Yellow Emperor), though this is legendary rather than historical. The oldest text claimed to preserve Xia-period calendrical knowledge is the Xia Xiaozheng (夏小正 Xià Xiǎozhèng, “Minor Almanac of the Xia”), transmitted within the Da Dai Liji (大戴禮記). It characterises months by which constellations are visible at dusk, the direction of the Northern Dipper’s handle, and seasonal agricultural tasks — but contains no computational astronomy.

Shang Dynasty — The First Written Calendar (c. 1600–1046 BCE)

The oracle bone inscriptions from 殷墟 Yínxū provide the earliest directly attested calendar in China. The Shang calendar used the sexagenary cycle to record days, organised time into ten-day 旬 xún weeks based on the Heavenly Stems, and alternated months of 29 and 30 days. A year contained 12 to 14 months, with intercalary months placed at the year’s end. Eclipse observations and nova records appear alongside calendar notations. The Shang new year fell on the first day of the twelfth month of the later Xia system — the month following the winter solstice.

Zhou Dynasty and the Six Ancient Calendars (1046–256 BCE)

The Zhou period saw the calendar develop from a practical agricultural tool into a sophisticated astronomical system. The Zhou Bi Suanjing (周髀算經 Zhōu Bì Suànjīng), one of the oldest Chinese mathematical-astronomical texts, describes the gnomon (圭表 guībiǎo) method for measuring the sun’s shadow and discusses the gaitian (蓋天, “heavenly lid”) cosmological model.

During the Warring States period, competing states maintained their own calendars. These are collectively known as the “Six Ancient Calendars” (古六曆 Gǔ Liù Lì):

All six are “quarter-remainder calendars” (四分曆 Sìfēn Lì) calculating the year as 365¼ days. The astronomers 甘德 Gān Dé and 石申 Shí Shēn (both c. 4th century BCE) produced the earliest known star catalogues, recording positions for 121 stars across the 28 lunar mansions (二十八宿 èrshíbā xiù). The 19-year Metonic cycle (7 intercalary months in 19 years) was established during this period.

Qin Unification — The Zhuanxu Calendar (221–206 BCE)

The Qin empire adopted the 顓頊曆 Zhuānxū Lì empire-wide. Under this system, the year began in the tenth month (roughly November), with the intercalary month placed at the year’s end as “the second ninth month” (後九月 hòu jiǔyuè). The early Han dynasty inherited this calendar.

The Taichu Reform — Foundation of the Modern Calendar (104 BCE)

Commissioned by 漢武帝 Hàn Wǔdì (Emperor Wu of Han), the reform was carried out by the astronomers 落下閎 Luòxià Hóng (156–87 BCE) and 鄧平 Dèng Píng, with 司馬遷 Sīmā Qiān contributing to the project. The Taichu Calendar defined the solar year as 365.2502 days and the synodic month as 29.53086 days. It achieved remarkable accuracy in planetary calculations — Mercury’s synodic period was measured at 115.87 days (modern value: 115.88 days) — and established a 135-month eclipse cycle. It is the oldest Chinese calendar whose computational data survive in full, preserved in the Shiji and the Hanshu (漢書 Hànshū).

Later Han astronomers continued to advance the field. 賈逵 Jiǎ Kuí (30–101 CE) observed that the winter solstice point had shifted against the fixed stars — an early recognition of the precession of the equinoxes (歲差 suìchā). 劉洪 Liú Hóng’s Qianxiang Calendar (乾象曆 Qiánxiàng Lì) was the first to correctly model the Moon’s varying orbital velocity and calculate the “true new moon” (定朔 dìngshuò). 張衡 Zhāng Héng (78–139 CE) invented a water-driven armillary sphere and described the cosmos as “the sky is round like a pill, the earth like the yolk of an egg.”

Zu Chongzhi’s Daming Calendar — Precession Enters the Calendar (462 CE)

Zu Chongzhi distinguished between the sidereal year (恒星年 héngxīng nián) and the tropical year (回歸年 huíguī nián) and calculated the tropical year at 365.24281 days (modern value: 365.24220 — extraordinarily close). His draconic month measurement of 27.21223 days differs from the modern value by only one ten-thousandth of a day. He successfully predicted eclipses four times over 23 years. Zu Chongzhi is also celebrated for calculating π as between 3.1415926 and 3.1415927, a precision record unsurpassed for nearly 900 years.

Sui Reunification and the Interpolation Breakthrough (581–618 CE)

After centuries of division, the Sui dynasty reunified China and its calendar. The most significant intellectual contribution came from 劉焯 Liú Zhuó (544–610 CE), whose Huangji Calendar (皇極曆 Huángjí Lì) applied equal-interval second-order difference interpolation to model the irregular motions of the Sun and Moon — a mathematical method that became a distinctive feature of Chinese computational astronomy. Although never officially adopted, it profoundly influenced the Tang calendars that followed.

Tang Dynasty — Yi Xing and the Dayan Calendar (727 CE)

Yi Xing’s Dayan Calendar (大衍曆 Dàyǎn Lì, completed 727 CE) introduced several breakthroughs. He compiled a solar motion table using the Dingqi method (定氣 dìngqì), calculating each solar term by the sun’s actual ecliptic longitude at 15° intervals rather than dividing the year into equal time segments. He invented unequal-interval second-order and third-order difference interpolation to handle the non-uniform motions of celestial bodies. The Dayan Calendar’s organisational structure — dividing all computations into seven major sections — became the model for all subsequent Chinese calendars.

Earlier in the Tang, 李淳風 Lǐ Chúnfēng (602–670 CE) had produced the Linde Calendar (麟德曆 Líndé Lì, 665 CE), which was the first to apply the “true new moon” method (定朔法 dìngshuò fǎ) to the everyday calendar (rather than only for eclipse prediction) and which abolished the ancient intercalary cycle in favour of observation-based methods.

Song Dynasty — Refinement and Innovation (960–1279 CE)

The Song dynasty saw more than 18 official calendars in its 300-year span, reflecting an era of intense astronomical activity. 沈括 Shěn Kuò (1031–1094 CE), in his Dream Pool Essays (夢溪筆談 Mèngxī Bǐtán), proposed a radical Twelve-Qi Calendar (十二氣曆 Shí’èr Qì Lì) — essentially a pure solar calendar with 立春 Lìchūn as New Year’s Day, dispensing with intercalary months entirely. Though never adopted, it anticipated the logic of the Gregorian system.

蘇頌 Sū Sòng constructed the celebrated water-powered astronomical clock tower (水運儀象臺 shuǐyùn yíxiàng tái) in 1092 CE, with over 150 mechanical components and armillary instruments — a forerunner of the modern planetarium. 楊忠輔 Yáng Zhōngfǔ’s Tongtian Calendar (統天曆 Tǒngtiān Lì, 1199 CE) determined the tropical year as 365.2425 days — identical to the average Gregorian year, established 383 years before the Gregorian reform of 1582. Yang also proposed that the tropical year’s length changes over centuries, with ancient values being longer.

Guo Shoujing and the Shoushi Calendar — The Pinnacle (1281 CE)

Commissioned under the Yuan dynasty, the Shoushi Calendar was the product of five years of intensive work (1276–1280) by a team assembled from both the Jin and Song astronomical bureaus. Guo Shoujing designed revolutionary instruments: the Simplified Instrument (簡儀 jiǎnyí), which reformed the armillary sphere and led the world for over 300 years; a 40-foot High Gnomon (高表 gāobiǎo) that reduced measurement error to one-fifth; and the Zenith Instrument (仰儀 yǎngyí) using pinhole projection.

The team established 27 observation stations spanning from the South China Sea (15°N) to the Bohai region (65°N) — an unprecedented national survey. The calendar adopted a tropical year of 365.2425 days and employed triple interpolation (三次內插法 sāncì nèichā fǎ) for solar and lunar motion calculations, together with an arc-chord method akin to spherical trigonometry.

Ming Dynasty — The Datong Calendar and the Jesuit Encounter (1368–1644 CE)

The Ming dynasty adopted the Shoushi Calendar largely unchanged, renaming it the Datong Calendar (大統曆 Dàtǒng Lì). Minor adjustments were made — sunrise times recalculated for Nanjing, the epoch reset to 1384 — but the computational methods remained identical. This calendar served the Ming for its entire 276-year duration.

By the late 16th century, accumulated errors had become noticeable. In 1629, 徐光啟 Xú Guāngqǐ (1562–1633) was appointed to lead a calendar reform project, assisted by Jesuit missionaries who introduced concepts from Copernicus, Kepler, and Tycho Brahe. The resulting Chongzhen Calendar was completed but not issued before the fall of the Ming in 1644.

Summary of Major Calendar Reforms

Heavenly Stems (天干 Tiāngān)

Earthly Branches (地支 Dìzhī)

The twelve Earthly Branches map to zodiac animals, two-hour periods (時辰 shíchen), compass directions, and months:

The Sexagenary Cycle (六十干支 Liùshí Gānzhī)

Lunisolar Mechanics

The Chinese calendar is neither purely lunar nor purely solar — it is a lunisolar (陰陽合曆 Yīnyáng Hélì) system that weaves both together. Think of it as two clocks running simultaneously: one tracks the moon, the other tracks the sun. Together they produce a calendar that stays aligned with both celestial cycles and the seasons.

Gregorian vs. Chinese Calendar — A Quick Comparison

What’s in a Name? The Naming History of the Chinese Calendar

For thousands of years, the Chinese calendar needed no special name — it was simply the calendar (曆 lì). Each dynasty gave its official calendar a specific title — the Taichu Calendar, the Shoushi Calendar, the Datong Calendar — but no generic label was necessary because no competing system existed in daily life. That changed abruptly in 1912, and the naming confusion that followed persists to this day.

Before 1912: Every Calendar Had Its Own Name

In imperial China, the right to promulgate the calendar was an exclusive imperial prerogative. The physical almanac distributed to the public was called 皇曆 huánglì (“imperial calendar”) because it was issued under imperial authority, or 黃曆 huánglì (“yellow calendar”) after the colour of its cover. Popular annotated almanacs with divinatory content were called 通書 tōngshū. These names described the calendar’s authority or format, never its type — because no competing system required differentiation.

1912: Two Calendars, Two Names Required

On 2 January 1912, 孫中山 Sūn Zhōngshān (Sun Yat-sen), provisional president of the newly founded Republic of China, decreed the adoption of the Gregorian calendar for official use. For the first time in Chinese history, two calendar systems coexisted — and both needed names to tell them apart.

The Gregorian calendar acquired several labels: 陽曆 Yánglì (“solar calendar”), 新曆 Xīnlì (“new calendar”), 西曆 Xīlì (“Western calendar”), 公曆 Gōnglì (“common calendar”), and in Taiwan 國曆 Guólì (“national calendar”). The traditional lunisolar calendar, meanwhile, was retroactively labelled with a grab-bag of informal names: 舊曆 Jiùlì (“old calendar”), 陰曆 Yīnlì (“lunar calendar”), and eventually 農曆 Nónglì (“agricultural calendar”).

農曆 Nónglì — The “Agricultural Calendar”

The term 農曆 is not an ancient name. It gained official status in 1947 when the Republic of China government rebranded the traditional calendar to emphasise its agricultural function. After 1949, the People’s Republic of China retained the term, and in 2017 standardised it in national standard GB/T 33661-2017 (《農曆的編算和頒行》). The earliest documented use in a publication title is the Zhejiang Agricultural Advancement Society’s 農家曆 (“Farmer’s Calendar”) of 1922.

The name carries an irony: the agricultural component of the Chinese calendar — the 24 Solar Terms that guide farming — is actually the solar component, not the lunar one. The months (which are lunar) have no particular agricultural significance. Calling the entire system the “agricultural calendar” is like naming a bicycle after only one of its wheels.

陰曆 Yīnlì — The Misleading “Lunar Calendar”

The colloquial habit of calling the Chinese calendar 陰曆 probably arose because the most visible feature — months beginning on the new moon, festivals falling on the 15th (full moon) — is lunar. But this is a fundamental misclassification. A true lunar calendar, such as the Islamic Hijri calendar, tracks only the moon. It has no intercalary correction and drifts through the seasons: Ramadan can fall in summer one decade and winter the next. The Chinese calendar, by contrast, uses the 24 Solar Terms and intercalary months precisely to prevent this drift. Its dual nature — lunar months anchored by solar terms — is its defining characteristic.

“Lunar Calendar” in English — A Mistranslation of a Misnomer

The English term “lunar calendar” for the Chinese system is a direct translation of the already-imprecise 陰曆. It compounds the error by stripping away the context that Chinese speakers at least implicitly understand — that 陰曆 is shorthand, not a technical description. In English, “lunar calendar” is taken at face value, leading to the widespread but incorrect belief that the Chinese calendar is a purely lunar system.

The correct English term is lunisolar calendar. The Chinese calendar shares this classification with the Hebrew calendar, the Hindu calendar, and the traditional Korean and Vietnamese calendars (which are historically derived from Chinese models). The Islamic Hijri calendar is the world’s most widely used true lunar calendar.

A Guide to the Names

The 24 Solar Terms (二十四節氣 Èrshísì Jiéqì)

24 Markers of the Sun's Path

UNESCO Intangible Cultural Heritage since 2016

Historical Development

Jié vs. Qì

Complete Reference Table

The Calendar in Daily Life

For millennia the Chinese calendar governed the rhythm of daily existence. Farmers relied on Solar Terms to determine planting and harvest times. Wedding dates, funerals, business openings, and travel were all selected according to auspicious calendar calculations. The BaZi system draws its four pillars directly from the sexagenary cycle of the birth date and time. Feng shui practitioners use the calendar to calculate Flying Star periods and determine temporal energy shifts.

For an in-depth discussion of the “Chinese New Year” vs. “Lunar New Year” naming debate and its cultural significance, see our sister site ChineseNewYear.wiki.

The Modern Custodian: Purple Mountain Observatory (紫金山天文台 Zǐjīnshān Tiānwéntái)

The Chinese agricultural calendar (農曆 Nónglì) is the only major traditional calendar system in the world that is officially computed and promulgated by a national scientific institution using modern astronomical methods. That institution is the Purple Mountain Observatory (紫金山天文台 Zǐjīnshān Tiānwéntái) in Nanjing — and its founding is itself a story of national dignity and scientific determination.

Origins: The 1913 Humiliation

In 1913, Japan organised an "Asian Observatory Directors' Conference" (亞洲觀象台台長會議 Yàzhōu Guānxiàngtái Táizhǎng Huìyì) in Tokyo. China — then in the chaos of the early Republic, with warlordism and political fragmentation — was initially not even invited. Gao Lu (高魯 Gāo Lǔ, 1877–1947), who had studied engineering in Belgium and served as director of the Central Observatory, attended under pressure from Japanese organisers who reluctantly allowed a Chinese delegate. Gao Lu felt deep humiliation: China, with over three millennia of astronomical tradition, had no modern national observatory. Japan, which had historically adopted the Chinese calendar system, now had multiple modern observatories. From that moment, Gao Lu resolved that China must build its own.

Establishment

On November 20, 1927, following Sun Yat-sen's posthumous wishes, the Nationalist government convened the preparatory meeting for the National Central Research Academy (國立中央研究院 Guólì Zhōngyāng Yánjiūyuàn, Academia Sinica). Gao Lu formally submitted his proposal: 《建國立第一天文台在南京紫金山》 ("Establish the Nation's First Observatory on Purple Mountain, Nanjing"). After vigorous advocacy, the proposal was approved. The Institute of Astronomy was founded in 1928 as one of Academia Sinica's first eight institutes, with Gao Lu as its first director.

The Purple Mountain Observatory was completed on September 1, 1934, housing a 60cm Carl Zeiss reflecting telescope — the largest in the Far East at the time. It is known as the "Cradle of Modern Astronomy in China" (中國現代天文學的搖籃 Zhōngguó Xiàndài Tiānwénxué de Yáolán), as nearly every subsequent Chinese astronomical institution was founded from or related to PMO.

Computing the Agricultural Calendar Today

The observatory's most culturally significant role is computing the Chinese agricultural calendar (農曆 Nónglì). In May 2017, China issued a formal national standard (GB/T 33661-2017, 《農曆的編算和頒行》 Nónglì de Biānsuàn hé Bānxíng) establishing the official rules for calendar computation, requiring accuracy to within approximately one second, and designating PMO as the sole authoritative institution.

Why "Lunar Calendar" Is a Misnomer

The Chinese calendar is frequently miscalled a "lunar calendar." This is technically incorrect. A pure lunar calendar — such as the Islamic Hijri calendar — tracks only moon phases, with a year of approximately 354 days that drifts through all seasons over a 33-year cycle. The Chinese calendar is a lunisolar (陰陽合曆 Yīnyáng Hélì) system: it integrates lunar months with the 24 Solar Terms, which are entirely solar in nature, anchoring the calendar to the seasons. This is why Chinese New Year always falls between January 21 and February 20 — the solar component prevents drift. The Chinese name 農曆 (Nónglì, "agricultural calendar") reflects this seasonal dimension. The calendar is no more "lunar" than it is "solar" — it is both, by design.

Frequently Asked Questions