我国古代长期采用阴阳合历，它根据月亮的盈亏变化定月，平年12个月，6个大月30天，叫“大尽”；6个小月各29天，叫“小尽”；全年354天。这比太阳年(365.2422天)要少约10天21小时。为此古人采取置闰的办法加以调整，开始时每三年闰一个月，五年闰两个月，春秋中叶后规定十九年闰七个月·每逢闰年加的一个月叫"闰月"，闰月加于某月之后叫"闰某月"。通过置闰可使历年的平均长度约等于一个太阳年，并和自然季节大致吻合。

置闰法图式

_______________ │________________________│_____________________

巽四宫·································离九宫·································坤二宫

阳遁····································阴遁····································阴遁

立夏四一七···························夏至九三六···························立秋二五八

小满五二八···························小暑八二五···························处暑一四七

芒种六三九···························大暑七一四 ··························白露九三六

_______________ │________________________│_____________________

震三宫 ··········································································兑七宫

阳遁 ·············································································阴遁

春分三九六·························中五宫···································秋分七一四

清明四一七·····································································寒露六九三

谷雨五二八·····································································霜降五八二

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艮八宫································ 坎一宫·································乾六宫

阳遁 ··································· 阳遁····································阴遁

立春八五二··························冬至一七四···························立冬六九三

雨水九六三··························小寒二八五···························小雪五八二

惊蛰一七四··························大寒三九六···························大雪四七一

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置闰法的定局

置闰法严格执行干支纪时，并适时调整跟上节气的变化。每一局的六十个时辰都是从甲子时起的六十甲子完整周期，即使在置闰时段，也是三个六十甲子完整周期， 故能够在一个节气中，形成十八次九星值符小循环、二十次八门值使小循环、二次九星中循环。在一年中，有二十四个节气用局的大循环，还有六次六十天的甲子循环，七十二次六十个时辰的甲子循环，四十八次九星的中循环，若遇置闰，九星的中循环一年五十次，正好是大衍之数.超者，超过也。神者，日辰也。接者，承接也。气者，诸节也。节气未至而日辰先到，则复节气为主而超越用未来之节气，此之谓超。又有节气已至而日辰未到，则伏辰为主而待日辰至方接承节。盖其气来则日辰未至而奇星常用于前节，此之谓接也。如丙午年四月十三日壬申交立夏节上，然四月初五日甲子日。甲己是四仲日，已在立夏前九日矣，则合超，超先于甲子日，下用立夏上局奇，己巳后用甲局，此乃先得奇后 得节，凡作用取效为速。 按日干支与节气定局，以日干甲、己为符头，又遇日支、子、 午、卯、酉用上元，遇寅、申、巳、亥用中元，遇辰、戌、丑、未，用下元，每五天一局，每个节气三局，一年二十四节气共七十二局，则每年剩余天数累积多达九天以上时，在夏至或冬至前重复上一节气的三局，谓之置闰，又称超神接气。

超接置闰法

超神

谓节气未至而甲子、己卯、甲午、己酉四上元之符头先到，则从符头而行节气之先 上元 。如正月初一日立春，而上年十二月二十五日即是甲子。此符头先至，即以此二十五日甲子作立春上元，至正月初一日乃行中元，故谓之超也。符头超越节气6天。

接气

谓 甲子、己卯、甲午、 己酉四上元之符头未到而节气先到，则候符头先日方行节气。如正月初一日立春，而初五方是甲子，此符头未到， 却以初一至初四仍行 大寒下元，至初五方行立春上元。故谓之接也。 符头晚节气4天。

置闰

每或四个上元符头与冬至日或夏至日超神有 超过八日（凡符头 起算 数到二至为9则置闰），在夏至或者冬至前闰上十五个日数，保留不排除此十五日延续至夏至或冬至日之后。 注:二至是指冬至夏至

超接诀

阴阳二遁，原洪进速。时未节气，先到迟时。节气交未来，超接通玄奥，日未来节先来，今日端然在割 裁。虽然节气已交度，奈何仲日未胚胎。先至节未至，超用未来节气，有时超起过旬余，所以积余成闰，位二至之前有 闰奇。此时叠积累乘之阳极阴终无定数，因立此闰毕。其余起法者，于逐年 芒种节上，于大雪前寻之。盖缘芒种节后是 夏至，则仪逆奇顺；大雪之后是 冬至，则仪顺而奇逆， 阳顺阴逆皆此也。

又诀凡节气或遇甲子、甲午、己卯、己酉，是甲己谓之正授。若不遇，则以官历挨究共过几日星当用第几局，名曰 超接。其造化，每至冬至多是超，至 十二三日又日闰也。

凡符头 起算 数到二至为9则置闰。

置闰歌歌诀

置闰歌歌诀

闰奇闰奇有妙诀，神仙不肯分明说。

甲己二日号符头，子午卯酉为上元。

寅申巳亥为中元，辰戌丑未下元节。

有时超过近一旬，便当置闰真妙诀。

要知置闰在何时，端在茫种与大雪。