Aside from the Gregorian Calendar System there is a widely used Persian Calendar System also known as the Jalali Calendar System which Coda does not support. This doc has a simple solution for supporting Persian Calendar System alongside the native date.
It simply includes a table of 366 records (equivalent to the amount of days in a leap year), named with auto generated columns (all formulas) mimicking the current Persian Calendar year (). Since its a simple Coda table, you can easily convert any Gregorian Calendar Date to any part of its equivalent Persian Calendar Date (or vice versa), using lookup or filter.
This solution is useful until Coda introduces a simple way of creating custom functions (e.g. using JavaScript) that could be used in formulas. Something like VBA scripts in Microsoft Excel or user-written Google Scripts that could be used as Add-ons on Google Sheets.
2023 Update: Since this solution only allows for working in one calendar year, I added ability to easily switch Jalali years with leap year considerations.
Use Case Examples
from Gregorian: to Jalali: () from Jalali: () to Gregorian: from Jalali Names: () to Gregorian: from Jalali (picked by date) to Gregorian
from Jalali (picked by name) to Gregorian
from Jalali (entered parts) to Gregorian
from Gregorian (entered) to Jalali (+ parts)
Changing the Jalali Year:
You can change the active Jalali Year for the whole JalaliCalendar table, by changing the JalaliActiveYear in the Page. A note about TimeZones (Troubleshooting):
When you pick a date from a date picker it uses the current timezone of the doc and stores the value. you can adjust the JalaliBaseEpoch variable accordingly to reflect your timezone, otherwise filters and lookups may not find the date in the JalaliCalendar table. Also do not forget to update all of your dates after changing the timezone of the doc.