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BaZi compatibility calculator
Enter two birth dates and get a structural comparison of both charts: how the two day masters relate, which elements each side supplies that the other lacks, and every clash, combination, punishment or harm that crosses between the charts. No matching percentage — the engine shows the evidence instead.
The short version
Classical BaZi compatibility is not one number, it is three separate comparisons: the two day masters (who each person is at the core), the five-element exchange (what each side brings that the other is missing), and the branch interactions between the charts (how the structures collide and bind). This page computes all three and shows the raw counts.
We deliberately do not average them into a compatibility score. Averaging three unrelated measurements manufactures precision the system does not have — and it hides the most useful part of the reading, which is which specific pair of characters is doing the work.
Compare two birth charts
Free · no sign-up · nothing stored
Both charts are computed with the same engine as the single-chart calculator, then compared. You can leave the birth times blank — the day master, element exchange and spouse palace comparison only need the dates.
How it’s calculated
- 1
Build both charts independently
Each birth date, time and place is resolved to its own four pillars — exactly as on the single-chart calculator, with the same solar-term boundaries and true solar time correction. Nothing between the two charts is shared or averaged at this stage.
- 2
Compare the two day masters
The day master (日主) is the character that anchors each chart. Comparing the two of them gives an element relationship — one generates, controls, or matches the other — and a ten-gods reading in each direction, because 甲 seeing 己 is not the same relationship as 己 seeing 甲.
- 3
Scan everything that crosses between the charts
Every stem in one chart is checked against every stem in the other, and every branch against every branch: 16 stem pairs and 16 branch pairs. Only the pairs that actually form a clash, combination, punishment or harm are reported, with the pillar positions named.
The full rule set — every convention, in order, with the engine field names — is published on the methodology page.
The three comparisons BaZi actually makes
Most online compatibility tools collapse everything into a zodiac pairing and a score. Classical 合婚 (marriage matching) works the other way round: it looks at a small number of specific, checkable things and reports what it finds. Three of them carry most of the weight.
The first is the day master comparison. The day master is the day stem — the character the whole chart is read relative to. Two day masters in a generating relationship (say Wood feeding Fire) describe a flow of support in one direction. Two in a controlling relationship describe structure, standards or pressure. Two of the same element describe a peer bond: easy recognition, and identical blind spots.
The second is the element exchange. Each chart has eight characters, tallied across the five elements. Frequently one chart is missing an element entirely and the other carries it. That is the most concrete thing compatibility reading can point at, because it is arithmetic rather than interpretation — and it is what people mean when they say two charts "complete" each other.
The third is the interaction scan: the same clash, combination, punishment and harm tables we use inside a single chart, applied across the pair. A combination between your month branch and their day branch binds two specific life areas; a clash between the two year branches creates tension between the two family lineages and the two public lives. The pillar positions are what make the reading specific — which is why we name them rather than just counting.
The spouse palace: one branch, read first
In classical readings the day branch (日支) is the spouse palace — the position closest to the day master, describing the domestic and intimate sphere. In compatibility work it is the first thing a practitioner looks at, because a relation between the two day branches is treated as a relation between the two domestic lives.
It is also the one comparison that survives an unknown birth time: your day pillar needs only the date, so the spouse palace comparison works even for three-pillar charts. The hour pillar — the one that does need a birth time — is the last thing to enter a compatibility reading, not the first.
One caution, and it is the reason we show the raw relation instead of a "spouse palace score": a combination here is binding, a clash here is tension, but neither is a judgement about the relationship. Classical texts disagree about how much weight to give it, and any tool that turns one branch pair into a percentage is inventing the number.
Why there is no compatibility percentage here
A matching score is the single most requested feature of a compatibility tool, and the one thing we will not ship. Here is the honest reason: the three comparisons above are not three measurements of one quantity. A pair with two clashing branches and a perfect element exchange is not "70% compatible" — it is a pair with a specific structure, and the useful output is which branch clashes and which element is supplied.
The second reason is that a percentage is unfalsifiable. Ours would be computed by an engine whose full rule set is published on the methodology page; if we cannot show you how 87% was derived, you have no way to check it, and neither do we.
What we give you instead is countable: how many cross-chart relations are binding and how many are in tension, which elements each side supplies, and where each interaction sits. You can disagree with the reading — that is the point. You cannot disagree with the arithmetic.
- Combinations, three-harmonies and directional meetings are counted as binding relations.
- Clashes, harms and punishments are counted separately as tension relations.
- The two counts are never added together, weighted, or converted into a single index.
Zodiac compatibility, and what it leaves out
Chinese zodiac compatibility is real BaZi — it uses the year branch, and the same six-combination and clash tables. The catch is that it uses one character out of eight, and the one that is least personal: the year pillar describes the generation and the family you were born into as much as it describes you.
That is why zodiac compatibility pages contradict each other. Snake and Monkey, for example, are simultaneously a six-combination and a punishment in the classical tables. A page that only wants a verdict picks one; the tables contain both, so we report both.
If you only have approximate birth dates and no times, the zodiac comparison is what you can actually get — and it is worth having. Just read it as a one-eighth sample, which is what it is.
A worked example
Two charts computed by this engine, then compared with the three-layer method. Both people are born in Taipei in the early 1990s, so the comparison is not a contrived pair. Every number below is the engine’s output — the same inputs reproduce it exactly.
Input
Person A
- Date
- 4 Feb 1990
- Time
- 10:00
- Place
- Taipei, Taiwan
- Time zone
- Asia/Taipei
己巳 丁丑 庚子 辛巳
Person B
- Date
- 20 Aug 1992
- Time
- 14:30
- Place
- Taipei, Taiwan
- Time zone
- Asia/Taipei
壬申 戊申 戊辰 己未
Day master relation
Earth generates Metal — B’s element generates A’s. The support runs from B toward A.
A sees B as 偏印 · B sees A as 食神
Cross-chart relations
5
binding
7
in tension
12
of 32 pairs
Reported separately, never averaged. Spouse palace (day branch × day branch): no pair-level relation.
Element exchange
A supplies Fire · B supplies nothing the other lacks · missing in both: Wood
Bars are counts of the eight characters in each chart (top bar: A, lower bar: B), scaled per element.
Read the structure, not a verdict
The pair has a strong generating link between the day masters and a real element dependency in one direction — and seven separate tension relations across the two charts, several of them doubled because the same branch pair appears more than once. That is a completely ordinary result: most pairs are structurally mixed. Nothing above says the pair is good or bad, and nothing above would change if you swapped which person is listed first.
Engine v1.1.0 · 16 stem pairs and 16 branch pairs checked across the two charts — these counts reproduce exactly from the four dates above.
Day master element matrix
The five-element relation between two day masters is arithmetic, not interpretation: read A’s element down the left, B’s across the top. Every one of the 25 combinations falls into exactly one of five relations — there is no gap and no overlap, which is why this part of a compatibility reading is not up for debate.
| A ↓ / B → | Wood木 | Fire火 | Earth土 | Metal金 | Water水 |
|---|---|---|---|---|---|
| Wood 木 | peer | A feeds B | A steers B | B steers A | B feeds A |
| Fire 火 | B feeds A | peer | A feeds B | A steers B | B steers A |
| Earth 土 | B steers A | B feeds A | peer | A feeds B | A steers B |
| Metal 金 | A steers B | B steers A | B feeds A | peer | A feeds B |
| Water 水 | A feeds B | A steers B | B steers A | B feeds A | peer |
Read it both directions: the same pair appears twice with opposite wording, because “A feeds B” and “B is fed by A” are the same relationship described from either end. Classical readings attach the ten-gods vocabulary on top of this — which is what the calculator reports as “A sees B as…”.
Pairs that carry two relations at once
The classical tables overlap, and this is where most zodiac-compatibility pages quietly take a side. A pair can be a combination and a punishment simultaneously — the relation count below is derived from the same tables the engine uses, so it is complete rather than selective.
- 巳申六合 Combination · 相刑 Punishment
- 丑未六冲 Clash · 相刑 Punishment
- 寅申六冲 Clash · 相刑 Punishment
- 寅巳六害 Harm · 相刑 Punishment
We keep every relation the tables contain rather than picking the flattering one. The same rule governs the sub-table inside a single chart.
Questions
- Is this a marriage-matching service?
- No. It is a structural comparison of two BaZi charts, and it is deliberately not romance-specific. People use it for partners, but the same comparison is used for co-founders, business partners, and for reading a parent and child together. Nothing in the output assumes a relationship type.
- Do I need both people’s exact birth times?
- No. The spouse palace comparison — the two day branches — needs only the dates, and the day master and element comparisons need only the dates too. Birth times add the hour pillar, which is the last part of the chart to enter a compatibility reading. You can run the comparison with dates alone.
- We have a clash between our charts. Does that mean we are incompatible?
- It means two specific branches in two specific positions are in opposition. A clash is the strongest structural tension in the system, and classical readings treat it as motion and friction rather than doom — it is also the relation that most reliably shows up as "something is always happening" in a pairing. What matters for a reading is where it sits: two year branches clashing is not the same as two day branches clashing.
- Why do your zodiac results sometimes say two signs are both a match and a punishment?
- Because the classical tables contain both, and they were never treated as mutually exclusive. Snake and Monkey are a six-combination and a punishment; Ox and Goat are a clash and a punishment. We keep every relation the tables contain rather than picking the one that makes a cleaner headline — the same rule applies inside a single chart.
- Is a two-person chart calculation private?
- Yes. Both charts are computed in your browser by the same engine the free calculator uses. No birth data is sent to our servers, and nothing is stored.
- How is this different from a percentage-based compatibility test?
- It reports evidence instead of a verdict. You get the day master relationship in both directions, the element exchange, and every cross-chart interaction with its two pillar positions named — and no aggregate score, because averaging three unrelated comparisons would invent a number the system does not support.
Next
Find your day master
The character the whole comparison is built on. Enter a date, get the stem and what it is read as.
OpenFive-element calculator
Run each chart separately to see the raw element counts behind the exchange.
OpenTen gods calculator
How one day master relates to another — the vocabulary used in the comparison above.
OpenFull chart
Get your own four pillars
The calculator is free and needs no account. It shows all four pillars, hidden stems, ten gods, your element balance and ten-year luck cycles — with the engine version on the result.
BaziPattern provides AI-generated readings for entertainment and cultural exploration purposes only. Readings are not predictions, or medical, legal, or financial advice.