# BaZi: the four pillars

**BaZi** (八字, "eight characters") is the four pillars of a birth: year, month, day and hour, each with its own heavenly stem and earthly branch. The pillars are the surface. The classical reading is built from what sits underneath them.

## Endpoints

### The pillars

| Endpoint | Credits | Returns |
|---|---:|---|
| `POST /v1/bazi/four-pillars` | 10 | All four pillars |
| `POST /v1/bazi/day-master` | 10 | The day master and its archetype |
| `POST /v1/bazi/ten-gods` | 10 | The ten gods relative to the day master |
| `POST /v1/bazi/luck-pillars` | 10 | 大運 luck pillars with the real 起運 start age |

### Chart analysis

| Endpoint | Credits | Returns |
|---|---:|---|
| `POST /v1/bazi/chart` | 20 | Everything below in one call |
| `POST /v1/bazi/hidden-stems` | 10 | 藏干: what each branch shelters, with role and weight |
| `POST /v1/bazi/element-balance` | 10 | Element balance over all eight characters, three ways |
| `POST /v1/bazi/na-yin` | 10 | 納音, the sound-element of each pillar |
| `POST /v1/bazi/life-stages` | 10 | 十二長生, the twelve stages |
| `POST /v1/bazi/symbolic-stars` | 10 | 神煞: peach blossom, travelling horse, canopy, nobleman, blade, void |
| `POST /v1/bazi/interactions` | 10 | 刑冲合害: combinations, clashes, harms, punishments |
| `POST /v1/bazi/strength` | 10 | Day-master strength in the 扶抑 framework |

## Hidden stems 藏干

Every branch shelters one to three stems, and this is where most of a chart's elements live. A chart with no visible Water can still be soaked in it.

Roles: **本氣** principal, **中氣** middle, **餘氣** residual. On the four storage branches (丑辰未戌) the middle role belongs to the element the branch **stores**, not to the second entry in the list: 丑 stores metal, 辰 water, 未 wood, 戌 fire. The list order follows the 人元司令 day counts, so on those four the second entry is the leftover of the previous season.

## Element balance

Three counts rather than one, because practitioners genuinely use different ones and a single number would be a school choice wearing the clothes of a fact.

| Field | What it counts |
|---|---|
| `balance.visible` | Four stems plus each branch's principal hidden stem: the classic eight |
| `balance.withHiddenStems` | Every sheltered stem, counted whole |
| `balance.weighted` | Each branch split among what it shelters, so the total stays at eight |

<Aside type="caution" title="Deprecated fields">
The top-level `elementCounts`, `dominantElement` and `missingElements` count **the year and month only**, four characters of eight, and never open the branches. They keep answering exactly as before until **2027-09-08** and carry RFC 8594 `Deprecation` and `Sunset` headers. Everything new lives under `balance`.
</Aside>

## Where the schools part

Five places, and each ships both readings rather than one.

| What | One reading | The other |
|---|---|---|
| Yin-stem direction through the twelve stages | 陽順陰逆 (`stageSchool=classical`) | 陰陽同生同死 (`stageSchool=unified`) |
| The yin blade 陰刃 | by 帝旺 | by 祿前一位 |
| The 庚 nobleman 天乙貴人 | 三命通會: 丑 and 未 | 淵海子平: 午 and 寅 |
| The element of the 午未 harmony | Earth | the sun-and-moon pair, no element |
| Strength thresholds | 0.55 / 0.45, our convention | no canonical rule exists |

## Day-master strength

One framework, and it is named: **扶抑**, support against suppression. Everything that produces or shares the day master supports it; everything else drains it.

Two limits are stated in the response itself. The month branch is counted like the other three, where the tradition weighs the month above all, and the 0.55 / 0.45 cut points are our convention rather than canon. So the three classical criteria (得令 season, 得地 root, 得勢 allies) are returned **unweighted** beside the ratio: a reader who weighs the month reaches their own verdict from the same inputs.

調候, 通關, 病藥 and 專旺 are other frameworks, are not applied here, and can reach the opposite verdict.

## True solar time

```bash frame="terminal"
curl -X POST https://api.astroway.info/v1/bazi/chart \
  -H "X-Api-Key: aw_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "date": "1995-06-15",
    "time": "09:20:00",
    "timezoneOffset": 8,
    "longitude": 75.9,
    "trueSolarTime": true
  }'
```

The correction reaches the **day and the hour**, and stops there: the year and month turn on instants of the world clock. Details and the cost of getting it wrong on the [conventions page](/en/chinese/conventions/).

## Example

<Tabs>
  <TabItem label="Whole chart">
    ```bash frame="terminal"
    curl -X POST https://api.astroway.info/v1/bazi/chart \
      -H "X-Api-Key: aw_live_..." \
      -H "Content-Type: application/json" \
      -d '{ "date": "1990-05-15", "time": "14:30:00", "timezoneOffset": 8, "language": "en" }'
    ```
  </TabItem>
  <TabItem label="Strength only">
    ```bash frame="terminal"
    curl -X POST https://api.astroway.info/v1/bazi/strength \
      -H "X-Api-Key: aw_live_..." \
      -H "Content-Type: application/json" \
      -d '{ "date": "1990-05-15", "time": "14:30:00", "timezoneOffset": 8 }'
    ```
  </TabItem>
</Tabs>