The intercalary month

In China there are two sets of calendars, one solar and the other one lunar = two different calendars. The solar calendar is longer, consisting of more days, than the lunar. Therefore, in order to avoid the lunar calendar lagging behind, an intercalary month is added every two or three years to keep the two calendars in sync.

When a lunar month does not contain a Qi of the 24 solar Jie Qi, it becomes a leap month.

 

The use of the intercalary month furthermore ensures that the Solstices and Equinoxes always fall in the same months in both the solar and the lunar calendars: the Spring Equinox in the 2nd (Mao), the Summer Solstice in the 5th (Wu), the Autumn Equinox in the 8th (酉), and the Winter Solstice in the 11th (branch-Zi).

There was an extra month added to the lunar calendar in 1936, 1938, 1941, 1944, 1947, 1949, etc. You can discover this info at this site, where the Gregorian/Western calendar is put together with the Chinese lunisolar calendar. See also list below.

ZWDS uses the lunar calendar, and when calculating a horoscope for someone born during a leap month, the intercalary month is divided in two, the first half belonging to the preceding month, and the second half to the succeeding one. Though this is one of those things in astrology where not everyone sticks to the same rule and chooses to do things differently. But I'll go with the cut the month in half formula.

Example: in the year 1968 there was an extra 7th month appended, including 24 August - 21 September. You can ascertain this here. A person born 27 August (first half of the intercalary month) would have been born on the fourth day of the 7th month (same as July 28). But if the person were born September 18 (second half), that would have meant being born on the 26th day of the 8th month (same as October 17).

Tables of the moon's phases can be found here. There is also a useful Chinese calendar service located at this site.

List of leap months 1900 - 2050

1900: from 24 September to (and including) 22 October

1903: 25 June - 23 July

1906: 23 May - 21 June

1909: 20 February - 21 March

1911: 26 July - 23 August

1914: 23 June - 22 July

1917: 23 March - 20 April

1919: 25 August - 23 September

1922: 25 June - 23 July

1925: 22 May - 20 June

1928: 22 March - 19 April

1930: 26 July - 23 August

1933: 23 June - 22 July

1936: 21 April - 20 May

1938: 25 August - 23 September

1941: 24 July - 22 August

1944: 22 May - 20 June

1947: 23 March - 20 April

1949: 24 August - 21 September

1952: 22 June - 21 July

1955: 22 April - 21 May

1957: 24 September - 22 October

1960: 24 July - 21 August

1963: 23 May - 20 June

1966: 21 April - 19 May

1968: 24 August - 21 September

1971: 23 June - 21 July

1974: 22 May - 19 June

1976: 24 September - 22 October

1979: 24 July - 22 August

1982: 23 May - 20 June

1984: 23 November - 21 December

1987: 26 July - 23 August

1990: 23 June - 21 July

1993: 22 April - 20 May

1995: 25 September - 23 October

1998: 24 June - 22 July

2001: 23 May - 20 June

2004: 21 March - 18 April

2006: 24 August - 21 September

2009: 23 June - 21 July

2012: 21 May - 18 June

2014: 24 October - 21 November

2017: 23 July - 21 August

2020: 23 May - 20 June

2023: 22 March - 19 April

2025: 25 July - 22 August

2028: 23 June - 21 July

2031: 22 April - 20 May

2033: 25 August - 22 September

2036: 23 July - 21 August

2039: 22 June - 20 July

2042: 22 March - 19 April

2044: 23 August - 20 September

2047: 23 June - 22 July

2050: 21 April - 20 May