Da yun starts at a specific age — here is where that number comes from
The Luck Cycles row on a BaZi chart, often labeled Da Yun (大运), shows a sequence of ten-year periods, each with a stem-branch pair and an age range such as 8–17 or 2–11. The first number is the starting age (起运). It is not a fixed convention like “always 10.” It is calculated from two inputs: which direction the cycles move from the Month Pillar, and how far the birth moment sits from a solar term.
Both inputs come from the birth year's Heavenly Stem polarity, the sex used for the traditional luck-cycle calculation, and the exact solar-term calendar. Change the sex parameter or cross a term boundary, and the first cycle or its starting age can change.
Direction: Yang-year males and Yin-year females move forward
The first cycle is derived by walking forward or backward from the Month Pillar, one stem-branch pair at a time along the sixty-year cycle. The traditional rule uses the polarity of the birth year's Heavenly Stem together with the sex used for the calculation: Yang males and Yin females move forward; Yin males and Yang females move backward.
The calculator labels this input as the sex used for the traditional luck-cycle calculation because it is a calculation parameter, not a statement about the person's identity.
Distance: count to the next or previous solar term
Once the direction is set, find the nearest Jie (节) — one of the twelve solar terms that starts a month pillar — in that direction. A forward chart counts from the birth moment to the next Jie; a backward chart counts to the previous one. The distance is measured in days and hours, not whole calendar days.
The classical conversion is three days equal one year, one day equals four months, and one shichen (two hours) equals roughly ten days. The remainder is converted into the displayed starting age in whole years. That is why two people born days apart in the same month can show different starting ages.
Because a solar term is a moment in time rather than a calendar date, the recorded local time, birthplace and any true-solar-time correction belong in the calculation.
A reproducible example: the same birth, two different starting ages
The case below is a synthetic regression example from this calculator's automated test suite, not a real user record. Enter the same inputs in the calculator and you should get the same numbers.
Birth: December 13, 1998, 12:00 local time, Beijing. The Year Pillar is 戊寅 (Yang Earth) and the Month Pillar is 甲子, the month that runs from the Dàxuě solar term to Xiǎohán. Because the year stem is Yang, the direction depends on the sex used for the calculation.
Counting forward reaches Xiǎohán roughly three weeks later, which converts to a starting age of about 8. Counting backward reaches Dàxuě about six days earlier, which converts to a starting age of about 2. The engine returns different first cycles for the two settings:
Why the exact moment and birthplace matter
The same birthday at different hours or places can sit on different sides of a term boundary, and true solar time can move the local moment by minutes or by more than an hour in a wide time zone. The starting age is therefore a location-aware calculation, not a lookup by date.
If two tools show different starting ages for the same birth, compare the resolved city, the historical clock basis, the solar-time convention and the term boundary before assuming one result is wrong. The systematic checklist in our guide on why BaZi calculators give different results walks through exactly those layers.
This calculator applies true solar time, resolves the historical local clock basis, uses solar-term boundaries and changes the day at midnight. Its da yun sequence follows the classical direction rule above.
What the chart shows — and what the number does not mean
When you calculate with an exact birth time, the chart lists nine ten-year da yun in order and highlights the current one. The starting age begins that sequence, and each following period starts ten years later.
The starting age is not a prediction of when life becomes good or bad. It is a timeline convention that decides where each stem-branch pair sits in the chart. Different schools can use different day boundaries or solar-time conventions, so the same birth can legitimately produce a neighboring starting age in another method.
The useful question is not whether the number feels accurate, but whether the rule is disclosed. Ours is: direction from the year stem's polarity and the sex used for the calculation, distance counted to the next or previous Jie, and the conversion at three days per year, shown as the starting age in whole years.
Method references
Sources and method notes
The linked pages describe the classical method and their own conventions; they do not prove a universal BaZi standard. The worked example above is a regression fixture from this calculator's own engine, so the same inputs should reproduce the same numbers.