Beginning of Spring立春

Beginning of Spring (立春, Lì Chūn) is the first of the twenty-four solar terms and the point where the BaZi calendar starts counting. It is an astronomical instant, not a day: the moment the sun reaches 315° of ecliptic longitude, which falls somewhere between 3 and 5 February depending on the year. Everything downstream in a chart — which animal year you belong to, which branch rules your month pillar — hangs off this one moment.

It is also easy to get wrong in English, because it competes with a more famous date. Lunar New Year is a lunisolar event that can land anywhere from late January to late February, and it is the day people celebrate. Beginning of Spring is a solar event that barely moves. For the year pillar, the tradition follows the solar one. If you were born in the gap between the two, the animal on the greeting card and the animal in your chart are not the same animal.

In the agricultural calendar the term opens the growing year: the cold has peaked, the ground begins to release, and preparation work starts even though nothing has visibly grown yet. The name promises less than it sounds like — 立 means "to set up" or "to establish", so 立春 is spring being declared rather than spring having arrived. Across most of the northern hemisphere, early February is still winter by the thermometer.

Astronomically it sits at the midpoint between the winter solstice and the spring equinox, which is why it is a cross-quarter term. The same structure produces Beginning of Summer, Beginning of Autumn and Beginning of Winter at the other three cross-quarter points, and all four are month-opening terms.

Beginning of Spring is a 節 — a month-opening term — so at that instant the month pillar's branch becomes 寅 (Yín). What makes it unique among the twenty-four is that the year pillar turns at the same moment. No other solar term moves the year. This is why practitioners describe the BaZi year as running from 立春 to 立春 rather than from one lunar new year to the next.

This site's calculator inherits that rule directly. Running the engine across 2026 as a check: at 2026-02-04 04:02 the pillars step from 乙巳 to 丙午 in the year and from 己丑 to 庚寅 in the month, both in the same instant. On 17 February 2026 — Lunar New Year that year, thirteen days later — nothing in the chart changes at all. A birth on 10 February 2026 is a 丙午 year in BaZi, even though the celebrations for that animal had not started yet.

One consequence worth stating plainly: because the boundary is an instant rather than a date, a birth on the boundary day can fall on either side of it. Somebody born at 02:00 on 4 February 2026 belongs to the previous year and the previous month; somebody born at 05:00 the same morning does not. This site computes the term times on the UTC+8 clock — the same basis as the official published tables — and reads the birth time you enter against them.

Lunar New Year (農曆新年) — Chinese lunisolar calendar. The two are close in the calendar and unrelated in mechanism. Lunar New Year is set by the moon and can fall anywhere from 21 January to 20 February; Beginning of Spring is set by the sun and moves by at most two days. The festival is what people celebrate, and the solar term is what the chart uses. Where they disagree — which is most years — the four pillars follow the solar term.

Rain Water (雨水) — The twenty-four solar terms. The next term after this one, two weeks later, and the other half of the 寅 month. Rain Water is a 氣 rather than a 節: it marks the middle of the month that Beginning of Spring opened, and it changes no pillar at all.