Julian Date Converter
Ancient Near Eastern research model
Babylonian Date Converter
Convert Gregorian dates to a schematic Babylonian lunar calendar model with a 19-year leap-month cycle, or convert model dates back to Gregorian.
Live output
Result
Choose a direction, enter a Gregorian or Babylonian schematic date, and the model result appears here.
Guide
Babylonian Date Converter for a schematic lunar model
This Babylonian Date Converter changes Gregorian dates into a schematic Babylonian lunar calendar model and converts model dates back into Gregorian dates. It uses alternating lunar month lengths and a 19-year leap-month cycle.
The page is a repeatable arithmetic research model, not an observed Babylonian month table. Historical Babylonian dates can depend on first visibility, local observation, royal administration, and tablet evidence that this converter does not reconstruct.
What this converter handles
Schematic Babylonian years, months, and leap Addaru II
The converter routes both directions through a Julian Day Number. Years are measured from the configured epoch, month lengths alternate 30 and 29 days, and schematic leap years add Addaru II as month 13.
Reverse input validates the leap-month suffix. A month 13 date is accepted only when the year is a leap year in this model and the input ends with -L.
Gregorian to Babylonian schematic
Enter a Gregorian date and return the model year, month name, day, 19-year cycle position, and reference JDN.
Babylonian schematic to Gregorian
Enter YYYY-MM-DD for regular months or YYYY-13-DD-L for leap Addaru II in a schematic leap year.
Leap-cycle disclosure
The page states its arithmetic leap cycle so results are not mistaken for observed historical month starts.
How to use it
Enter regular dates or leap Addaru II with -L
Choose Gregorian to Babylonian when your source date is Gregorian. Choose Babylonian to Gregorian when your source is already written in this schematic model's numeric format.
Regular input uses YYYY-MM-DD. Leap Addaru II uses month 13 plus the -L suffix, for example 1398-13-02-L when that year is a leap year in the model.
Convert from Gregorian
Enter a date such as 2026-06-30 to see the schematic Babylonian month and cycle-year position.
Convert from Babylonian schematic input
Enter values such as 1398-06-21 for regular months. Add -L only for month 13 leap Addaru II dates.
Do not infer observation records
Use the output as this page's arithmetic model result, not as proof of a historically observed lunar month start.
Reference examples
Reference conversions from the local implementation
These examples are calculated by the same local schematic functions used by the form. They show the regular month syntax and the JDN bridge used internally.
Gregorian to Babylonian schematic
The Gregorian date 2026-06-30 converts to Babylonian schematic 1398-06-21, shown as Ululu 21, Year 1398, with reference JDN 2461222.
Babylonian schematic to Gregorian
The Babylonian schematic date 1398-06-21 converts back to Gregorian 2026-06-30 in this 19-year model.
FAQ
Babylonian conversion questions
Babylonian calendar dates are historically complex because real months were observational and administratively recorded. These answers keep the page within its implemented schematic scope.
Is this an observed Babylonian calendar table?
No. It is a schematic arithmetic model with alternating lunar months and a fixed 19-year leap cycle.
What does -L mean?
-L marks leap Addaru II. The converter accepts it only with month 13 in years that are leap years in this schematic cycle.
Can this date a cuneiform tablet exactly?
Not by itself. Tablet chronology may require observed month starts, regnal years, location, and specialist historical evidence.
Reference
Calendar implementation reference
The implementation follows calendrical calculation practice by using an absolute day count and an explicitly stated arithmetic model. That makes the result repeatable and keeps the limitations visible.