Ten-Year Periods(大運)

There are two rules. Direction depends on the yin-yang polarity of your birth year's heavenly stem and your gender — men born in yang-stem years and women born in yin-stem years move forward, starting with the pair after the month pillar. The opposite combinations move backward, starting with the pair before it. Your starting age is calculated from the interval between birth and a seasonal boundary (jeol, 節). For forward cycles, count to the next boundary; for reverse cycles, count back to the previous one. Every three days becomes one year of age. One day equals four months, and one two-hour interval equals ten days.

Think of it as a “ten-year season”. The usual approach is to compare the period's stem and branch with your Day Master, assign their Ten Gods, and read those categories as the themes of the decade. A Wealth period brings money and practical gains to the foreground; a Resource period emphasizes learning and support. A period is not inherently good or bad. The reading focuses on what emerges as it interacts with your birth chart.

Seowoon does not calculate ten-year periods without gender information. The direction could be reversed, and guessing would amount to reading someone else's life. If your birth time is unknown, the engine uses noon and labels the result as an estimate — a twelve-hour difference shifts the starting age by about two months. If you were born on a seasonal boundary date, however, the time may change the month pillar itself, altering both the period's stem-branch pairs and starting age. Seowoon flags this separately. Ages use traditional Korean age counting.

The interval before your first ten-year period has no assigned stem-branch pair. If your first period begins at age eight, the preceding seven years are read from the birth chart alone. After that, the sequence moves to the next pair every ten years. Some schools read the stem and branch as the first and second five-year halves, but Seowoon treats the full ten years as one period.

Paid readings such as “Lifetime Record” show all ten periods in a table. The free “This Year's Fortune” reading examines the annual cycle within that backdrop, offering a first look at how the ten-year period acts as the background and the annual cycle as the weather.

People often say “your life turns upside down when your ten-year period changes”, but this backdrop changes every ten years for everyone. No period is inherently good or bad. The same period is read differently for each person depending on which characters it interacts with in their birth chart.The idea that a later starting age means you bloom late, or an earlier one means you bloom early, is also an interpretation, not a result of the calculation.