open the file _Prtg.DateTimePicker.js in an editor of your choice. It resides in the following folder:

C:\Program Files (x86)\PRTG Network Monitor\webroot\javascript

Search forfirstDay:1and change it tofirstDay:0

Of course you can use any other day of the week as well:

  • 0 - Sunday
  • 1 - Monday
  • 2 - Tuesday
  • 3 - Wednesday
  • 4 - Thursday
  • 5 - Friday
  • 6 - Saturday

  • Note

    This setting is not officially supported and you'll have to do these steps every time PRTG gets updated.