Each Luck Pillar (Da Yun, 大運) in Ba Zi lasts 10 years. They overlay your natal chart from a starting age determined by your gender and Year Stem polarity, and shift the elemental environment of your life decade by decade.
Short answer
Each Luck Pillar (Da Yun, 大運) in Ba Zi lasts 10 years. They overlay your natal chart from a starting age determined by your gender and Year Stem polarity, and shift the elemental environment of your life decade by decade.
In depth
Luck Pillars are calculated forward or backward through the 60-year sexagenary cycle from your Month Pillar. Yang-Year males and Yin-Year females progress forward; Yin-Year males and Yang-Year females progress backward.
The starting age varies based on the distance between your birth and the nearest Solar Term boundary. Most people start their first Luck Pillar between ages 1 and 10, with 8 being a common typical starting age.
Within each 10-year Luck Pillar, the Heavenly Stem governs the first 5 years and the Earthly Branch governs the second 5 years (with their interaction varying). This is why a major life shift around age 30 or 40 often correlates with a Luck Pillar transition.