Before Jingzhe: the Yin month remains

The Month Pillar does not change when the Gregorian month changes. It changes at the Jie, the twelve solar terms that divide the solar year into Bazi months. Jingzhe, which usually falls on 5 or 6 March, is the one that ends the Yin month.

A record dated 4 March 2026 still carries the Geng-Yin month even though the calendar on the wall says March. Readers who have compared two calculators and found a one-pillar disagreement very often turn out to be sitting in exactly this window: a date in the first few days of a Gregorian month, close to a Jie they did not know existed.

The useful habit is to stop thinking in months and start thinking in solar terms. There are twelve Jie in a year, so roughly one every thirty days, and each one moves the Month Pillar. If your birth date is within about two days of one of them, your Month Pillar is a question about minutes, not about which month you were born in.

The Month Pillar is also the pillar that carries the most downstream weight of the four in ordinary reading. It sets the seasonal context the Day Master is judged against, and it drives the Ten Gods mapping from the month stem and branch. A month pillar that is wrong by one position does not simply mislabel one column; it shifts a substantial part of how the chart reads as a whole.