ZWDS: Birth Time conversion

Zi Wei Dou Shu (紫微斗數), which is a form of Chinese astrology, accurate birth time is critical because it determines the placement of the 12 palaces and the key stars (like Zi Wei, Tian Ji, etc.) that define the destiny chart.

Why Solar Time Conversion is Important

China traditionally used the Lunar Calendar and based astrology calculations on solar time—not the modern standard time zones. This means that to cast a truly accurate Zi Wei Dou Shu chart, you must:

1. Convert local birth time to true solar time
   Because the sun’s position determines many of the astrological aspects, and solar time varies by:
   • Longitude (location of birth)
   • Time of year (due to Earth’s tilt and orbit)
     
2. Why Standard Time isn’t Accurate Enough
   For example, someone born at 3:00 PM in Beijing and someone born at 3:00 PM in a city far west of Beijing (but in the same time zone) will have different actual solar times. This can affect which “hour pillar” (時辰) or even which palace certain stars fall into.

How the Solar Time Conversion Works (in a simplified sense)

1. Get local time of birth (as recorded)
2. Adjust for time zone and daylight saving, if applicable
3. Calculate the local apparent solar time (LST) using:
   • The equation of time (accounts for Earth’s elliptical orbit and axial tilt)
   • The longitude of the birthplace
   • The standard meridian for the time zone
     
4. Here’s a simplified formula:

Solar Time = Local Time + 4*(Standard Meridian – Local Longitude) + Equation of Time

3. (Each degree of longitude represents 4 minutes of time.)
4. Use the corrected solar time to cast the Zi Wei chart

Example

• Birth: March 10, 1990, 3:00 PM in Chengdu, China (longitude ~104°E)
• China’s standard time: GMT+8, based on 120°E
• Difference: 120° – 104° = 16° → 16 x 4 = 64 minutes
• So, subtract 64 minutes from 3:00 PM → 1:56 PM solar time
• Then adjust further using the equation of time for March 10 (let’s say ~+10 mins) → Final solar time: ~2:06 PM

You’d use 2:06 PM solar time to determine the Zi Wei Dou Shu chart.

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Full charts, month by month, with the Earthly Branch hours and their solar time ranges.

🐀 January

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:30 – 1:30 (next day)
Chou	丑	The hour of the Ox	1:30 – 3:30
Yin	寅	The hour of the Tiger	3:30 – 5:30
Mao	卯	The hour of the Rabbit	5:30 – 7:30
Chen	辰	The hour of the Dragon	7:30 – 9:30
Si	巳	The hour of the Snake	9:30 – 11:30
Wu	午	The hour of the Horse	11:30 – 13:30
Wei	未	The hour of the Goat	13:30 – 15:30
Shen	申	The hour of the Monkey	15:30 – 17:30
You	酉	The hour of the Rooster	17:30 – 19:30
Xu	戌	The hour of the Dog	19:30 – 21:30
Hai	亥	The hour of the Pig	21:30 – 23:30

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🐂 February

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:40 – 1:40 (next day)
Chou	丑	The hour of the Ox	1:40 – 3:40
Yin	寅	The hour of the Tiger	3:40 – 5:40
Mao	卯	The hour of the Rabbit	5:40 – 7:40
Chen	辰	The hour of the Dragon	7:40 – 9:40
Si	巳	The hour of the Snake	9:40 – 11:40
Wu	午	The hour of the Horse	11:40 – 13:40
Wei	未	The hour of the Goat	13:40 – 15:40
Shen	申	The hour of the Monkey	15:40 – 17:40
You	酉	The hour of the Rooster	17:40 – 19:40
Xu	戌	The hour of the Dog	19:40 – 21:40
Hai	亥	The hour of the Pig	21:40 – 23:40

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🐅 March

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:50 – 1:50 (next day)
Chou	丑	The hour of the Ox	1:50 – 3:50
Yin	寅	The hour of the Tiger	3:50 – 5:50
Mao	卯	The hour of the Rabbit	5:50 – 7:50
Chen	辰	The hour of the Dragon	7:50 – 9:50
Si	巳	The hour of the Snake	9:50 – 11:50
Wu	午	The hour of the Horse	11:50 – 13:50
Wei	未	The hour of the Goat	13:50 – 15:50
Shen	申	The hour of the Monkey	15:50 – 17:50
You	酉	The hour of the Rooster	17:50 – 19:50
Xu	戌	The hour of the Dog	19:50 – 21:50
Hai	亥	The hour of the Pig	21:50 – 23:50

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🐇 April

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	00:00 – 2:00 (next day)
Chou	丑	The hour of the Ox	2:00 – 4:00
Yin	寅	The hour of the Tiger	4:00 – 6:00
Mao	卯	The hour of the Rabbit	6:00 – 8:00
Chen	辰	The hour of the Dragon	8:00 – 10:00
Si	巳	The hour of the Snake	10:00 – 12:00
Wu	午	The hour of the Horse	12:00 – 14:00
Wei	未	The hour of the Goat	14:00 – 16:00
Shen	申	The hour of the Monkey	16:00 – 18:00
You	酉	The hour of the Rooster	18:00 – 20:00
Xu	戌	The hour of the Dog	20:00 – 22:00
Hai	亥	The hour of the Pig	22:00 – 24:00

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🐉 May

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:10 – 1:10 (next day)
Chou	丑	The hour of the Ox	1:10 – 3:10
Yin	寅	The hour of the Tiger	3:10 – 5:10
Mao	卯	The hour of the Rabbit	5:10 – 7:10
Chen	辰	The hour of the Dragon	7:10 – 9:10
Si	巳	The hour of the Snake	9:10 – 11:10
Wu	午	The hour of the Horse	11:10 – 13:10
Wei	未	The hour of the Goat	13:10 – 15:10
Shen	申	The hour of the Monkey	15:10 – 17:10
You	酉	The hour of the Rooster	17:10 – 19:10
Xu	戌	The hour of the Dog	19:10 – 21:10
Hai	亥	The hour of the Pig	21:10 – 23:10

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🐍 June

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:15 – 1:15 (next day)
Chou	丑	The hour of the Ox	1:15 – 3:15
Yin	寅	The hour of the Tiger	3:15 – 5:15
Mao	卯	The hour of the Rabbit	5:15 – 7:15
Chen	辰	The hour of the Dragon	7:15 – 9:15
Si	巳	The hour of the Snake	9:15 – 11:15
Wu	午	The hour of the Horse	11:15 – 13:15
Wei	未	The hour of the Goat	13:15 – 15:15
Shen	申	The hour of the Monkey	15:15 – 17:15
You	酉	The hour of the Rooster	17:15 – 19:15
Xu	戌	The hour of the Dog	19:15 – 21:15
Hai	亥	The hour of the Pig	21:15 – 23:15

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🐎 July

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:20 – 1:20 (next day)
Chou	丑	The hour of the Ox	1:20 – 3:20
Yin	寅	The hour of the Tiger	3:20 – 5:20
Mao	卯	The hour of the Rabbit	5:20 – 7:20
Chen	辰	The hour of the Dragon	7:20 – 9:20
Si	巳	The hour of the Snake	9:20 – 11:20
Wu	午	The hour of the Horse	11:20 – 13:20
Wei	未	The hour of the Goat	13:20 – 15:20
Shen	申	The hour of the Monkey	15:20 – 17:20
You	酉	The hour of the Rooster	17:20 – 19:20
Xu	戌	The hour of the Dog	19:20 – 21:20
Hai	亥	The hour of the Pig	21:20 – 23:20

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🐐 August

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:10 – 1:10 (next day)
Chou	丑	The hour of the Ox	1:10 – 3:10
Yin	寅	The hour of the Tiger	3:10 – 5:10
Mao	卯	The hour of the Rabbit	5:10 – 7:10
Chen	辰	The hour of the Dragon	7:10 – 9:10
Si	巳	The hour of the Snake	9:10 – 11:10
Wu	午	The hour of the Horse	11:10 – 13:10
Wei	未	The hour of the Goat	13:10 – 15:10
Shen	申	The hour of the Monkey	15:10 – 17:10
You	酉	The hour of the Rooster	17:10 – 19:10
Xu	戌	The hour of the Dog	19:10 – 21:10
Hai	亥	The hour of the Pig	21:10 – 23:10

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🐒 September

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:00 – 1:00 (next day)
Chou	丑	The hour of the Ox	1:00 – 3:00
Yin	寅	The hour of the Tiger	3:00 – 5:00
Mao	卯	The hour of the Rabbit	5:00 – 7:00
Chen	辰	The hour of the Dragon	7:00 – 9:00
Si	巳	The hour of the Snake	9:00 – 11:00
Wu	午	The hour of the Horse	11:00 – 13:00
Wei	未	The hour of the Goat	13:00 – 15:00
Shen	申	The hour of the Monkey	15:00 – 17:00
You	酉	The hour of the Rooster	17:00 – 19:00
Xu	戌	The hour of the Dog	19:00 – 21:00
Hai	亥	The hour of the Pig	21:00 – 23:00

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🐓 October

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	22:50 – 0:50 (next day)
Chou	丑	The hour of the Ox	0:50 – 2:50
Yin	寅	The hour of the Tiger	2:50 – 4:50
Mao	卯	The hour of the Rabbit	4:50 – 6:50
Chen	辰	The hour of the Dragon	6:50 – 8:50
Si	巳	The hour of the Snake	8:50 – 10:50
Wu	午	The hour of the Horse	10:50 – 12:50
Wei	未	The hour of the Goat	12:50 – 14:50
Shen	申	The hour of the Monkey	14:50 – 16:50
You	酉	The hour of the Rooster	16:50 – 18:50
Xu	戌	The hour of the Dog	18:50 – 20:50
Hai	亥	The hour of the Pig	20:50 – 22:50

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🐕 November

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:10 – 1:10 (next day)
Chou	丑	The hour of the Ox	1:10 – 3:10
Yin	寅	The hour of the Tiger	3:10 – 5:10
Mao	卯	The hour of the Rabbit	5:10 – 7:10
Chen	辰	The hour of the Dragon	7:10 – 9:10
Si	巳	The hour of the Snake	9:10 – 11:10
Wu	午	The hour of the Horse	11:10 – 13:10
Wei	未	The hour of the Goat	13:10 – 15:10
Shen	申	The hour of the Monkey	15:10 – 17:10
You	酉	The hour of the Rooster	17:10 – 19:10
Xu	戌	The hour of the Dog	19:10 – 21:10
Hai	亥	The hour of the Pig	21:10 – 23:10

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🐖 December

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:20 – 1:20 (next day)
Chou	丑	The hour of the Ox	1:20 – 3:20
Yin	寅	The hour of the Tiger	3:20 – 5:20
Mao	卯	The hour of the Rabbit	5:20 – 7:20
Chen	辰	The hour of the Dragon	7:20 – 9:20
Si	巳	The hour of the Snake	9:20 – 11:20
Wu	午	The hour of the Horse	11:20 – 13:20
Wei	未	The hour of the Goat	13:20 – 15:20
Shen	申	The hour of the Monkey	15:20 – 17:20
You	酉	The hour of the Rooster	17:20 – 19:20
Xu	戌	The hour of the Dog	19:20 – 21:20
Hai	亥	The hour of the Pig	21:20 – 23:20

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🐍 June

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:15 – 1:15 (next day)
Chou	丑	The hour of the Ox	1:15 – 3:15
Yin	寅	The hour of the Tiger	3:15 – 5:15
Mao	卯	The hour of the Rabbit	5:15 – 7:15
Chen	辰	The hour of the Dragon	7:15 – 9:15
Si	巳	The hour of the Snake	9:15 – 11:15
Wu	午	The hour of the Horse	11:15 – 13:15
Wei	未	The hour of the Goat	13:15 – 15:15
Shen	申	The hour of the Monkey	15:15 – 17:15
You	酉	The hour of the Rooster	17:15 – 19:15
Xu	戌	The hour of the Dog	19:15 – 21:15
Hai	亥	The hour of the Pig	21:15 – 23:15

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🐎 July

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:20 – 1:20 (next day)
Chou	丑	The hour of the Ox	1:20 – 3:20
Yin	寅	The hour of the Tiger	3:20 – 5:20
Mao	卯	The hour of the Rabbit	5:20 – 7:20
Chen	辰	The hour of the Dragon	7:20 – 9:20
Si	巳	The hour of the Snake	9:20 – 11:20
Wu	午	The hour of the Horse	11:20 – 13:20
Wei	未	The hour of the Goat	13:20 – 15:20
Shen	申	The hour of the Monkey	15:20 – 17:20
You	酉	The hour of the Rooster	17:20 – 19:20
Xu	戌	The hour of the Dog	19:20 – 21:20
Hai	亥	The hour of the Pig	21:20 – 23:20

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🐐 August

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:10 – 1:10 (next day)
Chou	丑	The hour of the Ox	1:10 – 3:10
Yin	寅	The hour of the Tiger	3:10 – 5:10
Mao	卯	The hour of the Rabbit	5:10 – 7:10
Chen	辰	The hour of the Dragon	7:10 – 9:10
Si	巳	The hour of the Snake	9:10 – 11:10
Wu	午	The hour of the Horse	11:10 – 13:10
Wei	未	The hour of the Goat	13:10 – 15:10
Shen	申	The hour of the Monkey	15:10 – 17:10
You	酉	The hour of the Rooster	17:10 – 19:10
Xu	戌	The hour of the Dog	19:10 – 21:10
Hai	亥	The hour of the Pig	21:10 – 23:10

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🐒 September

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:00 – 1:00 (next day)
Chou	丑	The hour of the Ox	1:00 – 3:00
Yin	寅	The hour of the Tiger	3:00 – 5:00
Mao	卯	The hour of the Rabbit	5:00 – 7:00
Chen	辰	The hour of the Dragon	7:00 – 9:00
Si	巳	The hour of the Snake	9:00 – 11:00
Wu	午	The hour of the Horse	11:00 – 13:00
Wei	未	The hour of the Goat	13:00 – 15:00
Shen	申	The hour of the Monkey	15:00 – 17:00
You	酉	The hour of the Rooster	17:00 – 19:00
Xu	戌	The hour of the Dog	19:00 – 21:00
Hai	亥	The hour of the Pig	21:00 – 23:00

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🐓 October

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	22:50 – 0:50 (next day)
Chou	丑	The hour of the Ox	0:50 – 2:50
Yin	寅	The hour of the Tiger	2:50 – 4:50
Mao	卯	The hour of the Rabbit	4:50 – 6:50
Chen	辰	The hour of the Dragon	6:50 – 8:50
Si	巳	The hour of the Snake	8:50 – 10:50
Wu	午	The hour of the Horse	10:50 – 12:50
Wei	未	The hour of the Goat	12:50 – 14:50
Shen	申	The hour of the Monkey	14:50 – 16:50
You	酉	The hour of the Rooster	16:50 – 18:50
Xu	戌	The hour of the Dog	18:50 – 20:50
Hai	亥	The hour of the Pig	20:50 – 22:50

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🐕 November

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:10 – 1:10 (next day)
Chou	丑	The hour of the Ox	1:10 – 3:10
Yin	寅	The hour of the Tiger	3:10 – 5:10
Mao	卯	The hour of the Rabbit	5:10 – 7:10
Chen	辰	The hour of the Dragon	7:10 – 9:10
Si	巳	The hour of the Snake	9:10 – 11:10
Wu	午	The hour of the Horse	11:10 – 13:10
Wei	未	The hour of the Goat	13:10 – 15:10
Shen	申	The hour of the Monkey	15:10 – 17:10
You	酉	The hour of the Rooster	17:10 – 19:10
Xu	戌	The hour of the Dog	19:10 – 21:10
Hai	亥	The hour of the Pig	21:10 – 23:10

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🐖 December

Branch	Chinese	English Name	Time (Solar)
Zi	子	The hour of the Rat	23:20 – 1:20 (next day)
Chou	丑	The hour of the Ox	1:20 – 3:20
Yin	寅	The hour of the Tiger	3:20 – 5:20
Mao	卯	The hour of the Rabbit	5:20 – 7:20
Chen	辰	The hour of the Dragon	7:20 – 9:20
Si	巳	The hour of the Snake	9:20 – 11:20
Wu	午	The hour of the Horse	11:20 – 13:20
Wei	未	The hour of the Goat	13:20 – 15:20
Shen	申	The hour of the Monkey	15:20 – 17:20
You	酉	The hour of the Rooster	17:20 – 19:20
Xu	戌	The hour of the Dog	19:20 – 21:20
Hai	亥	The hour of the Pig	21:20 – 23:20