Two calendars give an animal to a year, and they do not change on the same day. The lunar calendar changes at Lunar New Year. The Four Pillars, or BaZi, calendar changes at Lichun, a fixed point in the Sun's yearly path. For most of the year the two give the same animal. For a few days or weeks around February they do not.
Two calendars, two boundaries
Lunar New Year: a new moon
Lunar New Year falls on a new moon between late January and mid-February. Because it follows the Moon, its date moves by up to several weeks from one year to the next. In 2025 it fell on January 29. In 2026 it falls on February 17, and in 2027 on February 6.
Lichun: the Sun at 315°
Lichun means "start of spring." It is the moment the Sun reaches 315° of ecliptic longitude. That point comes around once a year and lands on February 3, 4 or 5. The calculator finds the crossing by iterating on the Sun's computed position until it reaches 315°.
| Year | Lichun, New York | Lichun, Los Angeles | Lichun, London |
|---|---|---|---|
| 2025 | Feb 3, 9:10 am EST | Feb 3, 6:10 am PST | Feb 3, 2:10 pm GMT |
| 2026 | Feb 3, 3:01 pm EST | Feb 3, 12:01 pm PST | Feb 3, 8:01 pm GMT |
| 2027 | Feb 3, 8:46 pm EST | Feb 3, 5:46 pm PST | Feb 4, 1:46 am GMT |
Where the two disagree: 2025, 2026 and 2027
When the two boundaries fall on different days, a birth between them gets one animal from the lunar calendar and another from BaZi. The gap can open on either side.
| Window | Lunar calendar says | BaZi says |
|---|---|---|
| Jan 29, 2025 to Lichun on Feb 3, 2025 | Snake (new lunar year has begun) | Dragon, 甲辰 (Lichun has not come yet) |
| Lichun on Feb 3, 2026 to Feb 16, 2026 | Snake (lunar year not yet turned) | Horse, 丙午 |
| Lichun on Feb 3, 2027 (ET) to Feb 5, 2027 | Horse (lunar year not yet turned) | Goat, 丁未 |
In 2025 the lunar year came first, so late-January births were already Snakes in the lunar calendar and still Dragons in BaZi. In 2026 the order flips and the window is almost two weeks long. In 2027 it is a few days. In the UK and Ireland the 2027 window starts at 1:46 am on February 4.
On Lichun day itself, the hour decides
Lichun is a moment, so the date alone does not settle a birth on that day. In 2026 Lichun came at 3:01 pm in New York. A New York birth at 10 am on February 3, 2026 has the year pillar 乙巳, the Wood Snake. A birth at 4 pm the same day has 丙午, the Fire Horse. In London the same line fell at 8:01 pm, and in Los Angeles at 12:01 pm.
This is why the calculator asks for a birth time and a birthplace, not only a date. The place sets the time zone, and the time zone sets which side of the moment a local clock reading falls on.
Neither calendar is a correction of the other. They count different things. The lunar calendar counts moons. BaZi counts the Sun's position, and it uses that position for months as well as years.
Why BaZi uses the solar boundary
BaZi is built on the solar terms, the 24 points that divide the Sun's yearly path into 15° steps. Twelve of them, spaced 30° apart, open the twelve months. Lichun at 315° is the first of those twelve, so it opens both the first month and the year.
The twelve month-opening points sit at 315°, 345°, 15°, 45°, 75°, 105°, 135°, 165°, 195°, 225°, 255° and 285°. A month pillar changes when the Sun crosses one of them, not on the first of a calendar month.
The same solar terms set when the ten-year pillars of a BaZi chart begin. The distance in days from a birth to the next or the previous month-opening term, depending on the direction the chart runs, is divided by three to give the age at which the first ten-year pillar starts. Three days count as one year.
The month boundaries work the same way
The second month of the 2027 BaZi year, 癸卯, opens on March 5, 2027 at 2:39 pm in New York and 7:39 pm in London. The third, 甲辰, opens on April 4 at 8:17 pm in New York, which is already 1:17 am on April 5 in London.
A birth on the evening of April 4 in New York and a birth at the same instant in London have the same month pillar, even though their calendars show different dates. What counts is the instant.
All twelve month boundaries of the Fire Goat year →
What the calculator does
The free BaZi calculator places your birth on these same boundaries. It compares the instant of your birth with the instant of Lichun for the year pillar, and with the solar terms for the month pillar. The calculator page names this a "solar year boundary."
If you were born between late January and mid-February, enter your birth time and the calculator shows which side of Lichun your birth falls on. Without a time it reads the day at midday.