Indian national calendar
Enable an AI agent to recognise the Indian national calendar, assess whether a date or implementation follows its rules, and determine when conversion or official use is justified.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise the Indian national calendar, assess whether a date or implementation follows its rules, and determine when conversion or official use is justified.
The Indian national calendar is India's official civil Saka-era solar calendar, adopted by the Government of India in 1957, with twelve fixed-length months and leap years aligned to the Gregorian cycle, used alongside the Gregorian calendar in official communications.
It can be Identify a national calendar date while retaining ambiguity when only a Saka year or shared month name is supplied.; Validate month and day combinations using the applicable Saka year's leap status.; Convert complete dates to and from Gregorian dates with the rule basis and supported range recorded.; Check paired Saka and Gregorian dates in a document and flag discrepancies for review.; Render a verified date using evidenced month-name variants while preserving its calendar and era identity.; Determine whether a particular official communication supports or requires a national calendar date, using institution-specific evidence..
Distinguishing features
Require evidence of the national civil solar rules; a Saka year label alone does not establish this calendar. The national reform introduced a solar calendar for civil use. [Positional Astronomy Centre](https://packolkata.gov.in/INDIAN_CALADAR_PAC.pdf)
Check that Chaitra 1 corresponds to Gregorian March 22 in a common year and March 21 in a Gregorian leap year. [National Calendar](https://www.iipa.org.in/cms/public/uploads/123571650968187.pdf)
Check the fixed twelve-month pattern: Chaitra has 30 or 31 days, the next five months have 31 each, and the remaining six have 30 each. [Civil calendar rules](https://eclipse.gsfc.nasa.gov/SEhelp/calendars.html)
Distinguish adoption of the modern calendar on 22 March 1957 from the much earlier era used to number its years. [Press Information Bureau](https://www.pib.gov.in/PressReleasePage.aspx?PRID=1707068&lang=2®=48)
Scope
+ Identification of the national civil calendar and its Saka year numbering
+ Month order, day limits, leap-year determination and year rollover
+ Correspondence with Gregorian civil dates
+ Interpretation of multilingual month names and explicitly identified calendar dates
+ Evidence for official applicability and conformance of calendar representations
- Regional Hindu lunisolar calendars and their festival calculations
- Historical Saka-era chronology beyond its relationship to national calendar numbering
- Vikram Samvat and other neighbouring calendar systems
- Public holiday declarations and organisational working-day policies
- Astronomical ephemerides, tithis, nakshatras and astrological interpretation
- Clock synchronisation and time-zone rules, except as dependencies when assigning an instant to a civil date
Characteristics
- Calendar identification
- confirmed national civil calendar; ambiguous Saka usage; conflicting calendar evidence Prevents applying national calendar arithmetic to a regional calendar sharing its era or month names.
- Saka year correspondence
- For Gregorian year G, Saka year is G minus 78 from that year's Chaitra 1 onward, and G minus 79 before it. Prevents a one-year conversion error before the March new year. [Civil calendar rules](https://eclipse.gsfc.nasa.gov/SEhelp/calendars.html)
- Year class
- common or leap; evaluate Gregorian leap status for Saka year plus 78 Determines whether Chaitra has an additional day. [Civil calendar rules](https://eclipse.gsfc.nasa.gov/SEhelp/calendars.html)
- Ordered month vocabulary
- Chaitra, Vaisakha, Jyaistha, Asadha, Sravana, Bhadra, Asvina, Kartika, Agrahayana, Pausa, Magha, Phalguna; retain evidenced spelling variants Gives month names an unambiguous position for validation and conversion. [Month table](https://eclipse.gsfc.nasa.gov/SEhelp/calendars.html)
- Civil date validity
- valid; impossible day or month; incomplete; calendar ambiguous; outside supported range Controls whether an agent can convert a supplied expression or must seek more evidence.
- Gregorian correspondence discrepancy
- signed integer civil days between calculated and supplied Gregorian dates Exposes inconsistent dual dates and month-boundary mistakes.
- Application period
- post-adoption use; explicit proleptic calculation; historical calendar identity unresolved Separates mathematically extending modern rules backwards from interpreting an actual historical record.
- Official-use evidence
- documented for named institution and period; observed only; unverified; conflicting Prevents national designation from being treated as proof of a requirement in every workflow.
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
National calendar identity Establish which calendar a name, date or implementation denotes.
Saka numbering and traditional month names are insufficient to distinguish the national calendar from neighbouring systems.
Civil calendar recognition
Identify the national civil rule set behind an encountered representation.
National rules evidence
Record the designation and rule evidence supporting identification, retaining unresolved alternatives.
- What evidence establishes that this representation uses the Indian national civil calendar rather than another Saka-era calendar? definition
- Do its year start and month lengths agree with the national rules, or do lunar phases or regional conventions control them? boundary
Era and adoption
Separate inherited year numbering from the modern calendar's introduction.
Historical application boundary
Record whether a date reflects documented national calendar use, an explicit backward calculation or an unresolved historical convention.
- Which source supports applying the national calendar rules to the document's date and context? provenance
- For a date before the 1957 adoption, is this a declared proleptic conversion or an interpretation of an original Saka-era record? boundary
Saka year and month rules Capture the decisions that determine valid national calendar dates.
Recognition and safe arithmetic depend on the specific Chaitra leap adjustment and ordered month lengths.
Chaitra year boundary
Determine the start and leap class of a specified Saka year.
Leap-year selection
Record the Gregorian anchor year used to evaluate leap status and select the first day of Chaitra.
- Which Gregorian year corresponds to the start of this Saka year, and does it pass the Gregorian leap test including century exceptions? measurement
- Does that result place Chaitra 1 on March 21 or March 22 and allow or disallow Chaitra 31? measurement
Month sequence and limits
Resolve month position and allowed day numbers.
Month-day admissibility
Assess a supplied date against its resolved month and year class without silently repairing invalid input.
- Where does the resolved month fall in the Chaitra-to-Phalguna sequence, and how many days does it have in this year? measurement
- If the day exceeds that limit, should the agent reject it or request correction from the originating record? action
Gregorian correspondence Support conversion and reconciliation across the March year boundary.
The Saka year offset changes within a Gregorian year, making simple year subtraction unsafe.
Date conversion
Establish a complete, reversible correspondence between civil dates.
Anchored date mapping
Record the selected Chaitra anchor, elapsed civil days and resulting date in the other calendar.
- Does the Gregorian input fall before or on or after that year's Chaitra 1, and which Saka year follows? measurement
- Does conversion back to the original calendar reproduce the same year, month and day at Chaitra and Phalguna boundaries? measurement
Conversion preconditions
Distinguish civil date mapping from instant interpretation and unsupported historical extension.
Mapping readiness
Record missing date components, supported ranges and any external time-zone convention needed before conversion.
- Is the input a complete civil date, or an instant requiring an explicit time zone and day-boundary convention first? boundary
- When the calendar identity, year or supported historical convention is unresolved, which conversion must remain pending? action
National date expression Interpret and produce date labels without losing their calendar identity.
Multilingual spellings and shared Indic month names can make a correctly calculated date ambiguous in use.
Month-name interpretation
Resolve language, script and transliteration variants to national month positions.
Evidenced month alias
Preserve the supplied spelling and the evidence for interpreting it as a particular national calendar month.
- Which language-specific or official reference maps this spelling to a national calendar month? provenance
- Could the same label denote a regional lunar month, and what surrounding information resolves that ambiguity? boundary
Dual-date representation
Keep Saka and Gregorian labels explicit and mutually consistent.
Paired date integrity
Record which component belongs to each calendar and whether both designate the same civil day.
- Are the national calendar designation, Saka year and Gregorian companion date distinguishable in the document's notation? definition
- If the two dates disagree, what evidence determines which value can be corrected and which must remain disputed? action
Official application and conformance Assess the calendar's applicability to a particular publication or workflow.
An agent needs evidence about the receiving institution as well as correct date arithmetic before choosing an official representation.
Institutional use
Record requirements for the named institution, document type and period.
Document-specific applicability
Distinguish an evidenced dating requirement from an example of use or an unsupported assumption.
- Which dated instruction or publication establishes how this institution uses national calendar dates for this document type? provenance
- Does that evidence support a national date alone, a paired Gregorian date or another required presentation? action
Calendar output assurance
Evaluate a converter or calendar publication against evidenced civil rules and task boundaries.
Civil rule conformance
Record agreement with reference dates and prevent civil calendar correctness from being extended to unrelated holiday or ritual claims.
- Which independently sourced date pairs demonstrate correct behaviour around Chaitra 1, Chaitra 31 and Gregorian century exceptions? provenance
- Does the requested output require a separate holiday declaration or religious calendar calculation beyond national civil date conversion? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Official Indian national calendar (Saka Era, civil solar, 1957 reform)
- Traditional Saka / Shalivahana lunisolar calendars still used regionally
- Saka year numbering as an era overlay on other Indian calendars
- Which of these kinds and varieties hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q1134072 - Item for the Indian national calendar / Saka calendar as a calendar system.
- Which of these identifiers and schemes hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Calendar Reform Committee report (Government of India, 1955) leading to official adoption from 22 March 1957 / 1 Chaitra 1879 Saka
- Gazette of India practice: dual Gregorian and Saka dating of official notifications
- Which of these standards and regulation hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Printed on the Gazette of India, All India Radio news, and many Government of India communications together with the Gregorian date
- Used as the civil calendar for some official year-counts (Saka Era) while daily life and most business remain Gregorian
- Which of these real-world use hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Months per year - 12 - month
- Days in Chaitra - 30 (common year) or 31 (leap year) - day
- Saka year offset from Common Era - Saka year = CE year − 78 (from Chaitra/22 March onward) - year
- Which of these typical measurements hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Confusing the civil Saka calendar with regional Hindu lunisolar calendars that share month names but different new-year and leap rules
- Off-by-one year errors around 1 January-21 March, when the Saka year has not yet incremented
- Which of these failure modes and hazards hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Hindi and other Indian-language official use of Saka month names versus English Gregorian dating in most urban and commercial contexts
- Southern and eastern India more often use Tamil, Malayalam, Bengali, or other regional calendars rather than the national Saka civil calendar
- Which of these regional variation hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Hindu lunisolar calendar (panchanga) - The national calendar is a fixed solar civil scheme; a panchanga intercalates lunar months and is used for festivals and rites.
- Vikram Samvat - Vikram Samvat is a different era (about 57 BCE) used in parts of North India and Nepal; Saka Era epoch is 78 CE.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of Indian national calendar this model covers, and on what evidence? provenance
Sources
- Indian national calendar - Definition, month lengths, leap-year rule, 1957 adoption, official uses, and distinction from lunisolar Saka usage.
What the second pass must settle
- Which original adoption instrument and subsequent instructions establish the exact official-use requirements applicable to each institution and document type?
- Which authoritative conventions govern proleptic national calendar dates, year zero and dates before the modern calendar's adoption?
- Which official multilingual references settle accepted month spellings and aliases without importing regional calendar meanings?
- Which day-boundary and time-zone conventions should govern conversion from instants, especially for records created outside India?
- Which authoritative reference date pairs and software documentation establish supported ranges and correct treatment of Gregorian century exceptions?