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Calendars & date selection / ENCYCLOPEDIA

Calendar conversion

历法换算

Calendar conversion maps one day between date systems and requires explicit time conventions, leap-month labels and supported date ranges.

Introductory article2 min readUpdated 2026-09-30AI-assisted · Editorially checked

At a glance

Verification
Reverse-check the conversion and preserve leap status
One instant, different time labels08:00 UTC and 16:00 UTC+8 identify the same instant. Apparent solar time also depends on longitude and the equation of time; historical daylight-saving rules require checking.08:00 UTC16:00 UTC+08:00+ 8 hCivil zone time ≠ local apparent solar time
One instant, different time labels08:00 UTC and 16:00 UTC+8 identify the same instant. Apparent solar time also depends on longitude and the equation of time; historical daylight-saving rules require checking.

Definition and scope

Calendar conversion maps representations such as Gregorian and Chinese dates. Unlike date selection, it identifies a date rather than judging auspiciousness. Before using a table, establish the input calendar, leap-month status and covered years. A phrase such as the first day of a fourth month can remain ambiguous without these details.

[1][2]

Structure and details

Gregorian input generally needs year, month and day; Chinese input may also need a leap flag. A timed event first needs its relevant civil date. Lunar New Year and the Spring Commences boundary used by some chart traditions do not necessarily coincide. Conversion results should not silently substitute for every system’s year classification.

[1][2][3]

Example and history

Official observatory tables support birthday, festival and family-record checking. Convert a date and then reverse it using the same table; omitting the leap flag can break the round trip. Inspecting adjacent dates helps check month and year boundaries. This is a data-verification exercise requiring no astrological interpretation.

[1]

Contexts and limits

Historical conversion may require era names, reforms and allowance for recording errors. Software should state its supported range and explain invalid dates or missing leap status. Near-midnight events deserve attention to source conventions. A correct conversion faithfully represents time but does not establish personality or outcome predictions attached to that date.

[1][2]

References & further reading

Historical sources document ideas and rules of their time, not empirical proof of predictive accuracy. Source notes identify the nature and scope of each reference.

  1. Hong Kong Observatory: Gregorian–Lunar Calendar Conversion TableInstitutional / reference source

    Official calendar conversion tables; users must preserve leap-month labels and time conventions.

  2. Hong Kong Observatory: The Chinese Agricultural CalendarInstitutional / reference source

    Observatory explanation of lunar months, years and solar cycles, used for calendrical facts.

  3. Hong Kong Observatory: Date and Time of the 24 Solar TermsInstitutional / reference source

    Published solar-term event times must be read with the stated time standard.

Keep exploring

Lunisolar and Gregorian calendarsIntroduction24 solar termsIntroductionIntercalary monthsIntroductionAlmanacsIntroductionTwelve day officersIntroductionTraditional date selectionIntroductionTime zones and daylight savingIntroduction