《产经》云∶反支者，周来害人，名曰反支。若产乳妇人犯者，十死，不可不慎。若产
乳值反支月者，当在牛皮上，若灰上，勿令污水血恶物着地，着地则杀人。又浣濯皆以器盛
之，过此忌月乃止。
年立反支∶
年立子反支在申七月产忌；年立丑反支在酉八月产忌；年立寅反支在戌九月产忌；年立
卯反支在亥十月产忌；年立辰反支在子十一月产忌；年立巳反支在丑十二月产忌；年立午反
支在寅正月产忌；年立未反支在卯二月产忌；年立申反支在辰三月产忌；年立酉反支在巳四
月产忌；年立戌反支在午五月产忌；年立亥反支在未六月产忌。
年数反支∶
女年十三反支七月忌申；女年十四反支八月忌酉；女年十五反支九月忌戌；女年十六反
支十月忌亥；女年十七反支十一月忌子；女年十八反支十二月忌丑；女年十九反支正月忌寅；
女年二十反支二月忌卯；女年二十一反支三月忌辰；女年二十二反支四月忌巳；女年二十三
反支五月忌午；女年二十四反支六月忌未；女年二十五反支七月忌申；女年二十六反支八月
忌酉；女年二十七反支九月忌戌；女年二十八反支十月忌亥；女年二十九反支十一月忌子；
女年三十反支十二月忌丑；女年三十一反支正月忌寅；女年三十二反支二月忌卯；女年三十
三反支三月忌辰；女年三十四反支四月忌巳；女年三十五反支五月忌午；女年三十六反支六
月忌未；女年三十七反支七月忌申；女年三十八反支八月忌酉；女年三十九反支九月忌戌；
女年四十反支十月忌亥；女年四十一反支十一月忌子；女年四十二反支十二月忌丑；女年四
十三反支正月忌寅；女年四十四反支二月忌卯；女年四十五反支三月忌辰；女年四十六反支
四月忌巳；女年四十七反支五月忌午；女年四十八反支六月忌未；女年四十九反支七月忌申。
生年反支∶
子生女反支正月；亥生女反支二月；戌生女反支三月；酉生女反支四月；申生女反支五
月；午生女反支六月；午生女反支七月；巳生女反支八月；辰生女反支九月；卯生女反支十
月；寅生女反支十一月；丑生女反支十二月。
日反支∶
子丑朔六日反支；寅卯朔五日反支；辰巳朔四日反支；午未朔三日反支；申酉朔二日反
支；戍亥朔一日反支。
《产经》说：所谓“反支”，是指每月初一（朔日）向后推算的日子，被认为会给人带来灾祸，因此称为“反支”。如果产妇在月子里触犯了这个禁忌，有十条死路可走，必须极其谨慎。如果在产褥期遇到反支日或反支月，应当坐在牛皮上，或者坐在灰堆上，不要让污水、恶露等污秽之物接触地面；一旦接触地面，就会致人于死地。此外，所有的洗涤工作都要用容器盛接废水，直到过了这个忌讳的月份才能停止。
根据年支推算反支日的方法如下：
年支为子的人，反支日在申，七月分娩需忌避；年支为丑的人，反支日在酉，八月分娩需忌避；年支为寅的人，反支日在戌，九月分娩需忌避；年支为卯的人，反支日在亥，十月分娩需忌避；年支为辰的人，反支日在子，十一月分娩需忌避；年支为巳的人，反支日在丑，十二月分娩需忌避；年支为午的人，反支日在寅，正月分娩需忌避；年支为未的人，反支日在卯，二月分娩需忌避；年支为申的人，反支日在辰，三月分娩需忌避；年支为酉的人，反支日在巳，四月分娩需忌避；年支为戌的人，反支日在午，五月分娩需忌避；年支为亥的人，反支日在未，六月分娩需忌避。
根据年龄推算反支日的方法如下：
女子十三岁，反支日在七月忌申；十四岁，反支日在八月忌酉；十五岁，反支日在九月忌戌；十六岁，反支日在十月忌亥；十七岁，反支日在十一月忌子；十八岁，反支日在十二月忌丑；十九岁，反支日在正月忌寅；二十岁，反支日在二月忌卯；二十一岁，反支日在三月忌辰；二十二岁，反支日在四月忌巳；二十三岁，反支日在五月忌午；二十四岁，反支日在六月忌未；二十五岁，反支日在七月忌申；二十六岁，反支日在八月忌酉；二十七岁，反支日在九月忌戌；二十八岁，反支日在十月忌亥；二十九岁，反支日在十一月忌子；三十岁，反支日在十二月忌丑；三十一岁，反支日在正月忌寅；三十二岁，反支日在二月忌卯；三十三岁，反支日在三月忌辰；三十四岁，反支日在四月忌巳；三十五岁，反支日在五月忌午；三十六岁，反支日在六月忌未；三十七岁，反支日在七月忌申；三十八岁，反支日在八月忌酉；三十九岁，反支日在九月忌戌；四十岁，反支日在十月忌亥；四十一岁，反支日在十一月忌子；四十二岁，反支日在十二月忌丑；四十三岁，反支日在正月忌寅；四十四岁，反支日在二月忌卯；四十五岁，反支日在三月忌辰；四十六岁，反支日在四月忌巳；四十七岁，反支日在五月忌午；四十八岁，反支日在六月忌未；四十九岁，反支日在七月忌申。
根据出生年份的地支推算反支日的方法如下：
子年出生女子，反支日在正月；亥年出生女子，反支日在二月；戌年出生女子，反支日在三月；酉年出生女子，反支日在四月；申年出生女子，反支日在五月；午年出生女子，反支日在六月；午年出生女子，反支日在七月；巳年出生女子，反支日在八月；辰年出生女子，反支日在九月；卯年出生女子，反支日在十月；寅年出生女子，反支日在十一月；丑年出生女子，反支日在十二月。
根据日期推算反支日的方法如下：
初一为子日或丑日时，第六天为反支日；初一为寅日或卯日时，第五天为反支日；初一为辰日或巳日时，第四天为反支日；初一为午日或未日时，第三天为反支日；初一为申日或酉日时，第二天为反支日；初一为戌日或亥日时，第一天为反支日。
According to the *Chanjing* (Classic of Childbirth): "Fan Zhi" refers to specific days in the lunar month that are believed to bring harm, hence the name. If a woman in confinement violates this taboo, it is considered fatal, and one must be extremely cautious. If a postpartum woman encounters Fan Zhi days or months, she should sit on cowhide or on ash, ensuring that dirty water, lochia, or other impure substances do not touch the ground; touching the ground is said to cause death. Furthermore, all washing activities should be conducted using containers to catch the wastewater, and this practice should cease only after the taboo period has passed.
Calculation of Fan Zhi based on the Earthly Branch of the year:
For those born in the Year of Zi, Fan Zhi falls on Shen; July delivery requires avoidance. For those born in Chou, Fan Zhi falls on You; August delivery requires avoidance. For those born in Yin, Fan Zhi falls on Xu; September delivery requires avoidance. For those born in Mao, Fan Zhi falls on Hai; October delivery requires avoidance. For those born in Chen, Fan Zhi falls on Zi; November delivery requires avoidance. For those born in Si, Fan Zhi falls on Chou; December delivery requires avoidance. For those born in Wu, Fan Zhi falls on Yin; January delivery requires avoidance. For those born in Wei, Fan Zhi falls on Mao; February delivery requires avoidance. For those born in Shen, Fan Zhi falls on Chen; March delivery requires avoidance. For those born in You, Fan Zhi falls on Si; April delivery requires avoidance. For those born in Xu, Fan Zhi falls on Wu; May delivery requires avoidance. For those born in Hai, Fan Zhi falls on Wei; June delivery requires avoidance.
Calculation of Fan Zhi based on age:
A 13-year-old girl: Fan Zhi in July, avoid Shen. A 14-year-old: Fan Zhi in August, avoid You. A 15-year-old: Fan Zhi in September, avoid Xu. A 16-year-old: Fan Zhi in October, avoid Hai. A 17-year-old: Fan Zhi in November, avoid Zi. An 18-year-old: Fan Zhi in December, avoid Chou. A 19-year-old: Fan Zhi in January, avoid Yin. A 20-year-old: Fan Zhi in February, avoid Mao. A 21-year-old: Fan Zhi in March, avoid Chen. A 22-year-old: Fan Zhi in April, avoid Si. A 23-year-old: Fan Zhi in May, avoid Wu. A 24-year-old: Fan Zhi in June, avoid Wei. A 25-year-old: Fan Zhi in July, avoid Shen. A 26-year-old: Fan Zhi in August, avoid You. A 27-year-old: Fan Zhi in September, avoid Xu. A 28-year-old: Fan Zhi in October, avoid Hai. A 29-year-old: Fan Zhi in November, avoid Zi. A 30-year-old: Fan Zhi in December, avoid Chou. A 31-year-old: Fan Zhi in January, avoid Yin. A 32-year-old: Fan Zhi in February, avoid Mao. A 33-year-old: Fan Zhi in March, avoid Chen. A 34-year-old: Fan Zhi in April, avoid Si. A 35-year-old: Fan Zhi in May, avoid Wu. A 36-year-old: Fan Zhi in June, avoid Wei. A 37-year-old: Fan Zhi in July, avoid Shen. A 38-year-old: Fan Zhi in August, avoid You. A 39-year-old: Fan Zhi in September, avoid Xu. A 40-year-old: Fan Zhi in October, avoid Hai. A 41-year-old: Fan Zhi in November, avoid Zi. A 42-year-old: Fan Zhi in December, avoid Chou. A 43-year-old: Fan Zhi in January, avoid Yin. A 44-year-old: Fan Zhi in February, avoid Mao. A 45-year-old: Fan Zhi in March, avoid Chen. A 46-year-old: Fan Zhi in April, avoid Si. A 47-year-old: Fan Zhi in May, avoid Wu. A 48-year-old: Fan Zhi in June, avoid Wei. A 49-year-old: Fan Zhi in July, avoid Shen.
Calculation of Fan Zhi based on birth year branch:
Girls born in the Year of Zi have Fan Zhi in January. Girls born in Hai have Fan Zhi in February. Girls born in Xu have Fan Zhi in March. Girls born in You have Fan Zhi in April. Girls born in Shen have Fan Zhi in May. Girls born in Wu have Fan Zhi in June. Girls born in Wu have Fan Zhi in July. Girls born in Si have Fan Zhi in August. Girls born in Chen have Fan Zhi in September. Girls born in Mao have Fan Zhi in October. Girls born in Yin have Fan Zhi in November. Girls born in Chou have Fan Zhi in December.
Calculation of Fan Zhi based on the day of the month:
If the first day of the month (Shuo) is Zi or Chou, the sixth day is Fan Zhi. If the Shuo is Yin or Mao, the fifth day is Fan Zhi. If the Shuo is Chen or Si, the fourth day is Fan Zhi. If the Shuo is Wu or Wei, the third day is Fan Zhi. If the Shuo is Shen or You, the second day is Fan Zhi. If the Shuo is Xu or Hai, the first day is Fan Zhi.