Short answer: Synastry is the Western astrology method of comparing two birth charts to read the chemistry between two people, attraction, emotional fit and friction. Bazi compatibility compares two Chinese Four Pillars charts to read how your five elements support or clash over the long run. Synastry reads the spark, Bazi reads the foundation. They describe two different layers of the same relationship, which is why reading both tells you far more than either alone.
When two people wonder whether they fit, they usually reach for one of two very different tools without realising they answer different questions.
In the West, you compare star signs and, if you go deeper, you run a synastry chart. In Chinese tradition, families have compared Bazi charts for centuries before a marriage. Both look at two birth charts. Both are about compatibility. But they are reading two separate layers, and confusing them is why people get contradictory results and give up.
Here is what each one actually measures, and how to read them as a pair.
Synastry: the chemistry between you
Synastry is the astrology of relationships. The method is simple to picture: you take two birth charts and overlay one person's planets onto the other person's chart, then read the angles, what astrologers call aspects, that form between them.
What lights up is chemistry. When one person's Venus touches the other's Mars, there is attraction. When the moons connect, there is emotional understanding. Harsh aspects show where you rub each other the wrong way, and the famous North Node contacts hint at a sense of destiny or pull. Synastry is wonderful at the felt texture of a bond: how you spark, how you soothe each other, where you irritate.
What synastry says less about is the long structural question: across years and seasons, do your underlying energies feed each other or drain each other? For that, the Chinese system has a long head start.
Bazi compatibility: the foundation under you
Bazi compatibility compares two people's Four Pillars of Destiny charts. Each person has four pillars, year, month, day and hour, and each pillar carries a Heavenly Stem and an Earthly Branch tied to the five elements: wood, fire, earth, metal and water.
The reading looks at how those elements meet. Do your charts combine, where one person supplies the element the other lacks and the pair becomes more balanced together than apart? Or do they clash, where your strong elements collide and amplify each other's extremes? Traditional readers also look at how each person's day master, the element that represents them, relates to the other's, and at the combinations and clashes between the animal branches.
This is a structural, long-range view. It speaks to whether daily life together tends to settle into balance or tension, and how your timing cycles overlap. It is less about the first-date spark and more about the texture of year three and year ten.
Side by side
| Synastry (Western) | Bazi Compatibility (Chinese) | |
|---|---|---|
| Reads | Two charts overlaid, planet to planet | Two sets of four pillars, element to element |
| Strongest at | Attraction, emotional fit, the daily feel | Long-term balance, support or strain, timing |
| Key signals | Venus and Mars contacts, moon links, North Node | Element combine and clash, day masters, branch relations |
| Best question | How do we feel together right now? | Do we hold up well over the years? |
| Less suited to | The long structural arc | The moment-to-moment chemistry |
Why you want both
A relationship is not one layer, so one tool was never going to capture it. Plenty of couples have intense chemistry in synastry and a difficult elemental clash in Bazi: they feel magnetic and they exhaust each other. Others have gentle synastry and a beautifully balanced Bazi: quietly easy, built to last, occasionally needing a spark relit. You learn the most when you can see both readings at once and notice where they agree and where they pull in opposite directions.
And it is not only romance. Because Bazi compatibility simply reads how two people's energies interact, it applies to any close pairing: business partners, parent and child, siblings, close friends, collaborators. Any two people whose lives meet regularly can be read this way, with the same question underneath: where do we support each other, and where do we need patience?
One report, both layers
Reading synastry and Bazi by hand means two methods, two vocabularies, and the hard part of holding both in your head together. An integrated report removes that friction: both people's charts are computed across many systems at once and read as one picture.
Hour Light's Relationship User Manual crosses both birth charts through 37 systems, including synastry, Bazi compatibility and Zi Wei synastry, into a single 20-chapter manual: your two personalities, where your needs differ, where the friction lives, and how to be with each other. Each of you keeps a copy, and you can read it together.
One thing we hold firmly: a compatibility reading is never a score that decides your relationship. Charts that clash on paper often belong to couples who challenge and grow each other. The reading is a map of where you fit and where you will need patience, so you can meet those places with understanding instead of surprise. The choice to stay, and how to love well, stays entirely yours.
See both charts together
Read your relationship across 37 systems
Start free: enter both birth details and the 37-system synastry engine computes your compatibility together. When you want the full read, the Relationship User Manual turns it into a 20-chapter book for the two of you, kept in each of your libraries.
Relationship User Manual, NT$1,599 one-time / a copy saved for each of you
Frequently asked questions
What is the difference between synastry and Bazi compatibility?
Synastry overlays one person's planets onto the other's chart and reads the chemistry between you: attraction, emotional fit and friction. Bazi compatibility compares two Four Pillars charts and reads how your five elements interact, whether they support, balance or clash, which speaks more to long-term structure and timing. Synastry reads the spark, Bazi reads the foundation.
Is Bazi compatibility only about marriage?
No. It is often used for marriage matching, but it simply reads how two people's energies interact, so it applies to business partners, parent and child, close friends, family and collaborators. Any two people whose energies meet regularly can be read this way.
Does a low compatibility score mean we should not be together?
No. A reading is not a verdict. Charts that clash on paper often describe a couple who challenge and grow each other, while easy charts can drift into routine. The value is awareness: it shows where you fit and where you will need patience. What you do with that is your choice.
Do both people need their exact birth time?
For the most complete reading, both times help a lot. Synastry needs each time for the moon, rising sign and houses, and Bazi needs the hour to complete each person's four pillars. If one time is missing you can still read the date-driven parts, such as sun-sign dynamics and each person's day master, while the rest stays approximate.
Can you read synastry and Bazi compatibility together in one report?
Yes. An integrated report computes both charts across many systems at once and reads them as one picture, so you see the chemistry layer and the structural layer side by side. Hour Light's Relationship User Manual crosses both charts through 37 systems, including synastry, Bazi compatibility and Zi Wei synastry, into one 20-chapter manual.