How 大運 and 起運 are calculated: from solar term to ten-year cycles
Fix the direction from the year stem, measure the distance to the nearest 節, convert at 3 days = 1 year, and read the eight ten-year pillars.
What you will be able to do
You can work out the 起運 age yourself and check the tool against it; you can say where each 大運 step comes from; and you know why different tools disagree by a few months.
What you need first
- An accurate birth date and hour (a wrong hour means a wrong month pillar, and the whole 大運 sequence shifts with it)
- Birthplace: true-solar-time correction can push the birth moment across a solar term and change the 起運 age
- Gender: forward or backward is decided by the yin/yang of the year stem together with gender
01Decide forward or backward
The rule is 陽男陰女順行，陰男陽女逆行 — a yang year stem with a male, or a yin year stem with a female, counts forward; the other two combinations count backward.
What matters is the yin/yang of the **year stem**, not the zodiac animal and not the year branch. 甲, 丙, 戊, 庚 and 壬 are yang stems; 乙, 丁, 己, 辛 and 癸 are yin. Being born in a Rat year tells you nothing about this — you have to look at that year's stem.
- 01Read the year stem from your chart and classify it as yang or yin
- 02Combine that with your gender to get forward or backward
- 03Forward means counting toward the future; backward means counting toward the past
02Measure the distance to the nearest 節
Counting forward, measure from the birth moment to the **next** 節. Counting backward, measure from the **previous** 節 to the birth moment.
It has to be a 節, not a 氣. Only the twelve 節 (立春, 驚蟄, 清明, 立夏, 芒種, 小暑, 立秋, 白露, 寒露, 立冬, 大雪, 小寒) turn the month pillar; the 氣 — 雨水, 春分, 穀雨 and the rest — do not. Measure to a 氣 by mistake and the 起運 age drifts noticeably.
The moment needs to be precise to the minute. For 2026, 立春 falls at 02-04 04:02:08 — to the second. Use a date-only approximation like '4 February' and anyone born that day measures it wrong.
- 01Find the nearest 節 after the birth moment (forward) or before it (backward)
- 02Record that 節's exact moment and the birth moment
- 03Compute the difference in days, keeping the fraction rather than rounding
03Convert to a 起運 age
The traditional conversion is 3 days = 1 year and 1 day = 4 months, which gives: 起運 age = days of difference ÷ 3.
Our implementation clamps the result to between 0.3 and 12 years, so that malformed input cannot produce an absurd starting age.
**One simplification we disclose on purpose**: internally we compute a fractional age (4.7 years, say), but the eight 大運 steps are displayed using the truncated whole year (starting at 4). So the age ranges on screen are whole-year ranges, up to a year away from the '4.7 years' figure. That is known behaviour, not a calculation error.
- 01Divide the day difference by 3 to get the 起運 age
- 02Compare it with the tool's output; a gap under one year is that truncation
04Lay out the eight 大運 steps from the month pillar
The 大運 sequence starts from the month pillar: counting forward each step advances one place in the sixty-cycle (六十甲子), counting backward each step retreats one. So the first forward step is month pillar + 1, and the first backward step is month pillar − 1.
Each step governs ten years. We always output eight steps, covering roughly eighty years.
Why the month pillar? The month command (月令) is the outline of the chart, and the 大運 can be understood as that month command extended through time. It is also why a wrong hour or month pillar throws off the entire sequence.
- 01Find your month pillar
- 02Advance one place for forward, retreat one for backward — that is the first 大運
- 03Continue for eight steps of ten years each, starting from the 起運 age
05How to read a single 大運 step
Keep three layers apart: the natal chart is the ground, the 大運 is the backdrop for those ten years, and the 流年 (annual pillar) is the specific year inside it. A 大運 is not a verdict on its own — it does not stand without the natal chart and the annual pillar.
Reading usually splits in two: take the ten-god relation between the 大運 stem and your day master to name the decade's theme; then look at how the 大運 branch combines, clashes, punishes or harms the four natal branches to find where the friction sits.
The 大運 stem and branch also have their own strength, and whether they are supported or constrained inside the natal chart matters. Treat it as an environmental variable on a ten-year scale, not as a sentence.
- 01Name the ten-god relation between the 大運 stem and your day master
- 02Map the 大運 branch against the four natal branches and mark combinations and clashes
- 03Only then overlay the individual year, instead of concluding from the 大運 alone
Common mistakes
- Using the zodiac animal to decide direction
- Direction depends on the yin/yang of the **year stem** — the animal and the year branch are irrelevant. Someone born in a Rat year may have a 甲 (yang) or a 乙 (yin) stem, and the direction flips between them. Get this wrong and the whole sequence runs backwards.
- Measuring to a 氣 instead of a 節
- Only the twelve 節 turn the month pillar. Measuring to a 氣 such as 雨水 or 春分 makes the 起運 age noticeably too large or too small. Check which of the two you are looking at first.
- Ignoring true solar time
- After true-solar-time correction the birth moment can cross a solar-term boundary. This shows up most in high latitudes and far-western longitudes — Ürümqi's longitude correction reaches about −130 minutes. Cross the term and the 起運 age changes.
- Expecting every source to agree exactly
- '3 days = 1 year' is a widely used approximation. Computing to the hour or the double-hour, taking the solar-term table to the minute rather than the second, and switching true solar time on or off will each move the answer by a few months. A few months is a convention difference, not one side being wrong.
- Treating a 大運 as a standalone verdict
- A 大運 describes a ten-year backdrop. Reading it without the natal chart, or reading it without the annual pillar, produces conclusions that are far more definite than the method supports. There is no 'this 大運 will definitely do X'.
Read these concepts first
These are concept explanations with full entries in the knowledge base; this guide does not repeat their text.
Questions
Why is my 起運 age a few months off from another site?
Usually a convention difference rather than an error. Three common sources: how the conversion is rounded (fractional or whole, computed per day or per double-hour), how precise the solar-term table is (to the day, the minute, or the second), and whether true solar time is applied. Each of these can move the result by months.
Why does the 大運 sequence start from the month pillar?
The month command is the outline of the chart, and the 大運 is that command extended through time. Stepping forward or backward from the month pillar carries the birth month's stem and branch onward, producing a sequence that changes every ten years.
How long is one 大運, and how many are listed?
One step governs ten years. We always list eight, covering about eighty years. Listing ten or more is also traditional; it is a display choice and does not change the first eight.
Which matters more, the 大運 or the 流年?
Read them in layers: the natal chart is the ground, the 大運 is the ten-year backdrop, and the 流年 is the variable for the year. Usually you check whether the natal chart supports it, then what environment the 大運 provides, then what the year triggers. Any single layer on its own is unreliable.
What does clamping the 起運 age to 0.3–12 years mean?
It is a guard so that malformed input cannot produce an absurd result. For a normal birth time the 起運 age already falls inside that range; if the input is wrong, the result is clamped rather than reported as an extreme value.
All guides
See your own 大運
See your 大運 →Updated 2026-09-25