Julian Gregorian Old Style Offset Converter
Proleptic Julian civil date to proleptic Gregorian using existing JDN decoder. Positive years1–9998, no jurisdictional adoption, old-style year-start or era inference. Offset is the conventional calendar-rule difference evaluated at the resulting Gregorian date, not subtraction of potentially invalid Gregorian labels for Julian leap days.
Description
Julian and Gregorian calendars assign different nominal dates to the same civil day.
Julian and Gregorian calendars assign different nominal dates to the same civil day.1
A proleptic conversion applies ideal rules without establishing a place's historical adoption date. Use Julian Gregorian Old Style Offset Converter to evaluate the supplied inputs under the model explained below.
When to use Julian Gregorian Old Style Offset Converter
Use Julian Gregorian Old Style Offset Converter to evaluate the supplied inputs under the model explained below. Choose the applicable era, source or grammatical convention and independently establish the annotations or numerical assumptions.
How to use Julian Gregorian Old Style Offset Converter and understand its results
- Choose the applicable era, source or grammatical convention and independently establish the annotations or numerical assumptions.
- Enter Julian year, Julian month, Julian day using the field table and validation rules below, then run the tool.
- Read Proleptic Gregorian Date, Gregorian Minus Julian Nominal Days in the Result object; interpret the units, signs, ordering and unknown-value placeholders described below.
- Correct reported input errors and rerun. Apply successful results according to their specific meanings and check the assumptions before using them in a decision.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| julianYear | Julian year | number | Required; constraints below |
| julianMonth | Julian month | number | Required; constraints below |
| julianDay | Julian day | number | Required; constraints below |
Enter a real ideal-Julian date with integer year 1 to 9998, month 1 to 12 and valid day; years divisible by four are leap years. Convert through the Julian day number to a proleptic Gregorian date. Report the nominal calendar offset using the converted Gregorian year, adjusted to the preceding year for January/February. The offset can change by century and can be signed. No regional adoption, BCE input or historical intercalation is reconstructed.2
Julian date→JDN→proleptic Gregorian date; offset=floor(adjustedYear/100)−floor(adjustedYear/400)−2 Use the field order, units and branch conditions described above.
| Output field | Meaning | Value type |
|---|---|---|
| result | Object containing the named result fields below. | object |
| result.prolepticGregorianDate | Proleptic Gregorian Date | string |
| result.gregorianMinusJulianNominalDays | Gregorian Minus Julian Nominal Days | number |
{
"input": {
"julianYear": 1900,
"julianMonth": 2,
"julianDay": 29
},
"output": {
"result": {
"prolepticGregorianDate": "1900-03-13",
"gregorianMinusJulianNominalDays": 13
}
}
}Limitations and assumptions
A proleptic conversion applies ideal rules without establishing a place's historical adoption date. Apply the exact scope and assumptions explained above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse arrays fail validation. Domain-specific bounds, alignments and supported tokens are explained above; extremely large inputs or outputs can also be rejected. Input errors differ from successful false results, empty match lists and unknown-evidence placeholders.
Alternative or Complementary methods
Use Roman Calendar Kalends/Nones/Ides Converter for a related task: Roman date labels count inclusively toward Kalends, Nones or Ides.
Use Cleopatra Time Scale Moon Landing Pyramids Closer for a related task: Comparing BCE and CE events requires accounting for the absence of civil year zero.
References
Similar or alternative tools
- Roman Calendar Kalends/Nones/Ides Converter
Roman date labels count inclusively toward Kalends, Nones or Ides.
- Cleopatra Time Scale Moon Landing Pyramids Closer
Comparing BCE and CE events requires accounting for the absence of civil year zero.