Four pillars

Classical East Asian timekeeping tracks more than a calendar date. The year sets ancestral and social backdrop. The month captures seasonal energy — the climate and rhythm of when you were born — which is why most schools weight the month pillar heavily. The day anchors the person through the day element — the element on your day stem that stands in for you in every comparison, traditionally called the day master. The hour refines inner rhythm and later-life tone when birth time is known.

Without the hour pillar, three pillars still read — but the chart is less precise. We always ask for time when you can supply it.

Each pillar has two layers. The stem (top) is one of five elements — Wood, Fire, Earth, Metal, or Water — plus a ten god label: how that stem relates to your day element (for example peer, output, wealth, authority, or support). The branch (bottom) is one of twelve animal signs (Rat through Pig) with its own element and extra stems stored inside the branch.

On My Chart each card is drawn rather than spelled: a shape for the stem's element, a shape for the branch's animal, and a small mark under each for whether it is yang or yin. A key to all of them is in marks and symbols. The engine reads the structured chart; the cards translate it for reading.

1. Your birthplace picks the timezone, and the timezone turns your birth date and time into the local clock time we build from.
2. Year and month pillars follow the saju calendar. Month boundaries use solar terms— roughly two-week segments tied to the sun's position, not only the first of each Gregorian month.
3. Day pillar advances at midnight in your timezone. Some schools turn it at 11pminstead, which would move a birth in that last hour onto the next day’s pillar. That is a school’s choice rather than a mistake either way, and we make ours here so you can tell which one you are reading.
4. Hour pillar uses a two-hour branch window — each branch covers about two clock hours (for example 11pm–1am for Rat hour).

This app uses a deterministic saju engine — not an LLM — to compute pillars and every downstream read.

Worth saying plainly, because a practitioner will notice and a reader deserves to know before they take a boundary case to heart.

We read sun time, not clock time — when we know where you were born. A timezone is a political band, so a birth away from the meridian its zone is named for happens at a different solar hour than the clock says. Seoul keeps UTC+9, whose meridian runs through the sea east of Japan, so the sun there is about half an hour behind the clock. We shift the birth moment by that difference before reading the pillars, which can move a birth near the edge of a two-hour branch to the other side of it. The birth time we show you back is the one you entered — only the chart moves.

Our solar terms are calculated, not dated.This used to be the second thing on this list. A month boundary is now the moment the sun actually reaches its mark, solved from a NASA/JPL planetary ephemeris and stored to the second for 1901 through 2050 — so a birth on a boundary day is placed by its hour rather than handed the whole day's answer. It also means the boundary is one instant everywhere: the same birth reads the same whether you describe it in Seoul time or Los Angeles time. Outside those years we fall back to the older arithmetic estimate, which is accurate to about a day.

Some birthplaces have no coordinate. 1447 of the 1469 places in the picker resolve to a known longitude; the rest, and any place you type that we cannot match, are read from clock time and the chart says so in its own assumptions. We would rather leave a chart uncorrected than correct it by the wrong amount.

Away from the edges the remaining gap does not matter. Until it changes, this is what the chart in front of you was built from, and we would rather you knew than found out.

Four-pillar astrology developed in the Chinese calendar tradition and remains central in Korean saju practice. Practitioners refined pillar weighting, ten-god roles (how each stem relates to the day element), and five-element balance over centuries.

We do not claim to replicate every classical school. This product uses a documented modern engine with leanings-only copy — energy patterns for reflection, not fate or commands.