Published · Reviewed August 21, 2026
Solar-Term Month Boundaries
See the twelve solar-term boundaries used by Clarify's Month Pillar method, why exact times matter, and how to audit a near-boundary result without confusing it with a calendar month or forecast.
Also known as: BaZi month boundaries · Month Pillar solar terms · twelve solar-term months · Jié Qì Yuè Jiè · 节气月界
Plain-English answer
Clarify's Month Pillar does not change on the first day of each Gregorian month or each Chinese lunar month. The current engine measures solar longitude, takes Spring Commences at 315 degrees as the starting reference, and maps the circle into twelve 30-degree positions. Each position begins at a solar-term crossing, so a date printed in a calendar is only an approximate signpost. A near-boundary audit needs the exact birth instant, the exact crossing, the time zone, and the calculation version.
Concept overview
- English term
- Solar-Term Month Boundaries
- Chinese term
- 节气月界
- Pinyin
- Jié Qì Yuè Jiè
- Content status
- Published educational reference
Quick facts
- Twenty-four terms
- The Hong Kong Observatory describes 24 terms at 15-degree solar-longitude intervals, alternating between two sets of twelve.
- Twelve Month Pillar positions
- Clarify's current calculation groups the full 360-degree cycle into twelve 30-degree positions beginning at 315 degrees.
- Exact moment
- A boundary is the instant the calculated solar longitude crosses its target, not midnight across an entire conventional date.
- Month branch and stem
- The position determines the Month Branch; the current engine then derives the Month Stem from the BaZi Year Stem group and position.
- No forecast meaning
- Crossing a Month Pillar boundary changes a calculation field. It does not make a month lucky, dangerous, certain, or eventful.
The twelve boundary terms and Month Branch intervals
- Spring Commences · 315°
- Begins the Yin interval. This is also Clarify's current BaZi Year Pillar reference.
- Insects Waken · 345°
- Begins the Mao interval after one 30-degree step.
- Bright and Clear · 15°
- Begins the Chen interval after the longitude sequence wraps through zero.
- Summer Commences · 45°
- Begins the Si interval.
- Corn on Ear · 75°
- Begins the Wu interval.
- Moderate Heat · 105°
- Begins the Wei interval.
- Autumn Commences · 135°
- Begins the Shen interval.
- White Dew · 165°
- Begins the You interval.
- Cold Dew · 195°
- Begins the Xu interval.
- Winter Commences · 225°
- Begins the Hai interval.
- Heavy Snow · 255°
- Begins the Zi interval.
- Moderate Cold · 285°
- Begins the Chou interval, which continues until the next Spring Commences crossing.
Why not every solar term starts a BaZi month
The Observatory's English page calls the two alternating sets major and minor solar terms. Starting from Spring Commences, Clarify's month-position boundaries occur every 30 degrees at the series listed above. The intervening 15-degree terms remain real solar terms and useful calendar markers, but they do not start another one of Clarify's twelve Month Pillar positions.
Translation can make this confusing because English sources do not always map Chinese labels such as jie and zhongqi to major and minor in the same direction. The reliable audit is the named term plus target longitude and declared product rule—not an isolated translated adjective.
How Clarify currently calculates the Month Pillar
- 1. Resolve a reference instant
- Use the birth's recorded civil date and time with the applicable place-based time-zone rule when available.
- 2. Calculate solar longitude
- The engine evaluates the Sun's apparent longitude at that instant.
- 3. Measure from 315 degrees
- It normalizes the angular distance from Spring Commences across the 360-degree cycle.
- 4. Choose one of twelve positions
- The engine divides the normalized angle by 30 degrees to select a zero-based month position and maps it to a branch from Yin onward.
- 5. Derive the Month Stem
- The current formula combines the BaZi Year Stem group with the month position. A Year boundary correction can therefore propagate into the Month Stem.
- 6. Add a proximity flag
- The implementation flags a result very close to a 30-degree boundary for review. The flag asks for data verification; it does not add meaning.
Run a Month Boundary Audit
- Input snapshot Record local date, clock time, precision, place, IANA zone, longitude if used, and whether time is known.
- Boundary pair Identify the previous and next 30-degree target terms and calculate both crossing instants.
- Comparable clocks Show birth and boundaries in UTC and in the resolved birth zone. Do not compare a local birth clock with an unconverted Hong Kong table.
- Angular and time distance Record solar longitude, position, and signed time to the nearest boundary. This makes the decision reproducible.
- Pillar result Save the structured Month Stem and Branch from the engine, not a hand-typed or image-generated replacement.
- Impact set If the input or boundary side changes, recalculate strength, relations, timing, and every analysis module that used the old chart.
Worked boundary case without fabricated pillars
- Exact record
- The birth is thirteen minutes before the crossing, so the earlier position applies under the stated method.
- Rounded record
- If the source says about 14:00 with a plus-or-minus thirty-minute range, both positions remain credible candidate states.
- Wrong zone table
- If 14:18 was copied from another zone, convert it before deciding. The apparent thirteen-minute difference may be false.
- Changed Year Stem
- Even if the Month Branch position is stable, a Year boundary correction can require a different Month Stem under the current formula.
- Reading boundary
- The result can tell us which structured Month Pillar the selected method returns. It cannot prove what happens during that month.
Do not confuse three kinds of month
- Gregorian month
- A numbered civil-calendar unit beginning at local midnight on day one. It is useful for records and display.
- Chinese lunar month
- A moon-phase calendar unit that may require leap-month state. It is part of the Chinese calendar, but not Clarify's Month Pillar position.
- Clarify solar-term month
- One of twelve 30-degree solar-longitude intervals used by the current engine to calculate the Month Pillar.
Common mistakes
- Changing on the first of the month
- Gregorian day one is not the relevant boundary in this method.
- Using the lunar month number directly
- Calendar conversion and Month Pillar calculation are separate steps.
- Using all 24 terms as 24 BaZi months
- Clarify uses twelve 30-degree positions, not twenty-four Month Pillars.
- Treating a conventional date as exact
- The crossing has a time and must be displayed in the correct zone.
- Editing the Month Pillar by hand
- Correct the input or method, then regenerate all deterministic and dependent fields.
Frequently asked questions
- Why does my Month Pillar look one month behind?
- The comparison may be using a civil month label instead of the solar-term interval, or the calculators may use different methods or time normalization.
- Does birthplace affect the Month Pillar?
- It can affect which instant a recorded local clock time represents, especially close to a crossing. The solar-term event itself is not created by the place.
- Does true solar time set the Month Pillar in Clarify?
- The current engine uses the normalized civil instant for solar longitude and separately uses corrected time for the Hour Pillar. See the product method before comparing other systems.
- Should every nearby result show two readings?
- Only when credible input or method uncertainty crosses the boundary. Otherwise a proximity flag simply invites verification.
A Month Pillar is not a monthly verdict
This page explains a deterministic field under Clarify's declared method. It does not establish scientific prediction, fixed personality, career outcome, relationship event, health condition, or financial timing. Check any interpretation against the full method, current evidence, consent, and qualified advice where relevant.
Where to go next
- Time Zones
- Resolve local civil time before comparing it with a solar-term crossing.
- Birthplace and BaZi Calculation
- See how place selects a historical zone and, in Clarify, longitude for the hour-layer correction.
- How to Read a BaZi Chart
- Use the existing Guide for whole-chart reading after the calculation is verified.
Use with Clarify
Free BaZi Reading
Apply reviewed concepts only after Clarify calculates a complete chart.
Sources & editorial basis
- Clarify editorial sourceSupporting source recorded in the Claim Ledger.
- Clarify editorial sourceSupporting source recorded in the Claim Ledger.
- Clarify editorial sourceSupporting source recorded in the Claim Ledger.
- Clarify deterministic chart systemCurrent product implementation and tests; supports Clarify behaviour only.
- Clarify MethodologyCurrent calculation and editorial workflow; product-behaviour source.
- Clarify published BaZi guidesReviewed public guides used for terminology and learning-order continuity.
- Clarify DisclaimerCurrent product boundaries for interpretation and consequential decisions.
Source-to-claim locators are maintained in Clarify's editorial evidence record.