Working out Financial Week Number 2019/20 and beyond

lennox25 , Try like

FY Week = QUOTIENT(DATEDIFF(Minx(FILTER('Date',[FY Start Date]=EARLIER([FY Start Date])),'Date'[Start of Week]),[Date],DAY),7)+1

or go to a sunday/monday  of FY Start date

FY Week Start = [FY Start Date] - weekday([FY Start Date],2) +1 // Monday

FY Week = QUOTIENT(DATEDIFF(Minx(FILTER('Date',[FY Week Start ]=EARLIER([FY Week Start ])),'Date'[Start of Week]),[Date],DAY),7)+1

Creating Financial Calendar - From Any Month
https://community.powerbi.com/t5/Community-Blog/Creating-Financial-Calendar-Decoding-Date-and-Calendar-1-5-Power/ba-p/1187441
https://medium.com/chandakamit/cheat-sheet-calendar-of-any-standard-month-just-one-variable-apart-5ee47de6a208