The calendar settings control:

  • the first day of the week (any day Monday - Sunday)
  • which day(s) to mark red, and
  • week numbers

Week Numbers

Week Numbers are used in many countries but do not universally follow the same rules.

aCalendar offers the following choices for week numbers:

  • OFF (don't show)
  • Android OS (use the week numbering as determined by Android for your region)
  • ISO/Europe (starts on the Monday nearest to January 1)
  • America/Japan (starts on Sundays, January 1 is in week#1)
  • Custom (aCalendar offers 2 different custom week number definition methods) NEW in version 2.4
    • annually, e.g. starting every 1st Monday in April
    • fixed cycle, e.g. a 72-weeks cycle starting on January 20, 2018 


If you see week numbers shown as events, these are subscribed to from Google Calendar, and should best be turned off in the Calendar List.