It converts your local clock time to true solar time, casts the nine palaces by the Hour-based Rotating Plate (Chai-bu) method, and then explains what is on the chart in plain language.
Qimen Dunjia is the most structurally intricate of the Chinese divinatory arts: the moment is converted to stems and branches, the yin/yang cycle and the ju number are fixed, and then the nine stars, eight gates, eight spirits, and the heaven/earth stems are laid into nine palaces by rule. The whole derivation is deterministic — same moment, same longitude, same chart, for anyone.
This site uses the Hour-based · Rotating Plate · Chai-bu school, rolls the day at 23:00, and corrects clock time to true solar time by longitude (the clock face only — solar-term boundaries are untouched). Flying-plate, yin-plate, and intercalation rules from other schools are deliberately kept out: mixing schools is the single most common error here, and once mixed, charts can no longer be compared against each other.
There is no "close enough" in casting: it is either right or wrong. So it is pinned down in tests — the nine-palace diagrams from the books, one cell at a time. If a change to the engine puts a single cell out of place, the code does not ship.
Once the chart is cast, something still has to decide which palace answers your question. Get that wrong and every sentence afterwards is describing a different matter.
We publish that number, and we publish both rulers: across 321 casebook examples, it agrees exactly with the author 43.2% of the time, and lands somewhere within the set of palaces the author used 68.8% of the time. So it is usually in the right neighbourhood, but fully agreeing with the author happens less than half the time.
Why both: the loose ruler alone flatters us, since it counts “roughly right” as right; the strict one alone understates, since casebooks themselves often read several palaces for one question. A loose ruler makes you optimise the wrong thing, so we read both — and publish both. Not a flattering number, but the real one, and we keep working on it.
The reading text is generated by an AI from the cast chart. It is for reflection only and is not medical, financial, legal, or psychological advice, nor a substitute for a doctor, a lawyer, or a financial adviser. For decisions that matter, come back to the real world and talk to a professional.
First time looking at one of these? The app has a one-minute page explaining the nine palaces, the five symbols in each cell, and which cell is "you".
Casting, the 3D nine palaces, per-palace imagery, pattern analysis, and multi-palace combinations — free forever, no account needed.
Only the AI reading is metered, because each one is a real call to a language model. Signing in gives you 1 free reading (gifts are limited per network per day; the app says so if the quota ran out); after that:
Readings live on your account — switch devices or browsers and they are still there, and they do not expire. Payments are handled by Stripe; we never see your card number. Crisis responses, safety messages, and any attempt where the AI did not come through are never charged.
How is a Qimen Dunjia chart cast?
The moment of asking is converted into stems and branches; the solar term and its three periods fix the yin/yang cycle and the structure number; then the nine stars, eight gates, eight spirits, and the heaven/earth stems are laid into the nine palaces by rule. The whole derivation is deterministic — same moment, same longitude, same chart for everyone. This calculator does the entire conversion from your time and longitude.
Which Qimen school does this site use?
Hour-based, Rotating Plate, Chai-bu method, with the day rolling at 23:00. Rules from other schools — Flying Plate, Yin Plate, day/month/year charts, the Zhi-run intercalation — are never mixed in: once schools are mixed, charts can no longer be compared against each other.
What is the difference between Chai-bu and Zhi-run?
Both answer the same question: how to assign the structure number when the leader day and the solar term fall out of step. Chai-bu splits and patches at the nearest leader day; Zhi-run inserts a leap structure around certain solar terms. This site uses Chai-bu only, with no toggle.
Do I need true solar time?
Yes. Clock time in a unified time zone can differ from the actual solar time at your longitude by more than an hour — enough to cross an hour boundary and change the whole chart. This site corrects the clock face by longitude; solar terms are still judged by the real astronomical moment, unaffected by that shift.
Can I cast repeatedly for the same question?
Not recommended. One matter, one casting is this discipline's own rule: asking the same thing again does not make the chart more accurate, only the decision harder.
Is the chart casting verified?
Yes. The casting layer is compared cell by cell against 297 charts printed in classical masters' books — 11,868 cells, 100% match — plus an exhaustive 2,600-chart check of the plate rules with zero mismatches. These comparisons live in the test suite: if one cell disagrees after an engine change, the code cannot ship.
Is it free?
Casting, the 3D nine palaces, per-palace imagery, pattern analysis, and multi-palace combinations are free forever, no account needed. Only the AI reading is metered, because each one is a real call to a language model; signing in gives you one free reading (gifts are limited per network per day; the app says so if the quota ran out). Crisis responses, safety messages, and any attempt the AI failed to deliver are never charged.
Location is used only to compute true solar time and to show your city name. Casting happens entirely on your device and works offline. Only when you tap Read do your question and a summary of the chart go to the reading service to write that one reply — not stored, not tied to your identity. Signing in uses your email solely to remember your reading balance: no ads, never shared. See the Privacy Policy.