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You do not need any of this to use the tools. But if you want to know why your year pillar changed in February, or what a rising sign actually measures, this is the short version.
A Chinese chart is built from the birth moment, not the birth date. The moment is written as four pairs of characters — one pair for the year, one for the month, one for the day, one for the hour. Four pairs, eight characters: the BaZi, literally "eight characters".
Each pair combines one of ten heavenly stems with one of twelve earthly branches. The branch of the year is the animal everyone knows — but the animal is the least informative part of the chart. The stem of the day, the day master, is usually taken as the description of the person themselves.
The Chinese year does not begin at New Year, and it does not begin at Chinese New Year either. It begins at 立春, the start of spring, which falls in early February. If you were born in the second half of January or the first week of February, most quick calculators will give you the wrong animal — and the wrong year pillar underneath it.
The same logic runs through the whole chart. The month pillar changes at each of the twelve 节, the solar terms that mark the seasons, not on the first of the month. A birth moment therefore has to be placed against the actual sky, which is why our tool carries a solar-term table rather than a calendar approximation.
Every stem and branch carries one of five elements: Wood, Fire, Earth, Metal, Water. Count all eight characters and you get a distribution — a chart that is heavy in Fire and empty of Water, for instance.
Spring, east, morning. Growth, beginnings, the will to expand.
Summer, south, midday. Warmth, visibility, expression.
Late summer, centre, afternoon. Stability, digestion, holding things together.
Autumn, west, evening. Structure, discernment, letting go.
Winter, north, night. Depth, adaptability, reflection.
What practitioners look for is not a chart that is strong everywhere, but one where the elements are in proportion — and which one is carrying too little.
A Western chart is a map of where the planets were, seen from your birthplace, at your birth moment. It needs three things: the date, the exact time, and the place. The place matters because the sky looks different depending on where you are standing on the globe.
The Sun sign is the one everybody knows. The Moon sign describes the inner weather. The rising sign, or ascendant, is the sign that was climbing over the eastern horizon at the moment you were born — which is why it changes roughly every two hours, and why it is the part most sensitive to a missing birth time.
They are not rivals. Both take a single moment and a single place and describe what that configuration is like. The Western system cuts the sky into twelve signs and twelve houses; the Chinese system cuts the same moment into stems, branches and elements. Different instruments, same sky — which is the whole reason this site is named after a part that both instruments share.
Neither system can tell you what will happen, what you should do, or whether you are ill. They are languages for reflection — useful ones, with long histories — but they are not diagnosis and they are not prediction. Anyone selling you certainty is selling you something other than astrology.