Trend line - rolling 12 months

[Anonymous]

Hi everyone, I'm looking to create a trend line on a chart that shows a rolling 12 month calculation of % of Referrals that have work baskets .

My calculation is as follows which works perfectly to show a bar graph however I want to add a trend line to this.  Any help would be greatly appreciated!

=sum({1<[RECEIVED_DATE.autoCalendar.Date]={'>=$(=MonthStart(Max(RECEIVED_DATE.autoCalendar.Date),-12))<=$(=MonthEnd(Max(Today()),-1))'},WB_10,

[RECEIVED_DATE.autoCalendar.Year]=,[RECEIVED_DATE.autoCalendar.Month]=,[RECEIVED_DATE.autoCalendar.YearMonth]=>}WB_10)/

count({1<[RECEIVED_DATE.autoCalendar.Date]={'>=$(=MonthStart(Max(RECEIVED_DATE.autoCalendar.Date),-12))<=$(=MonthEnd(Max(Today()),-1))'},REF,

[RECEIVED_DATE.autoCalendar.Year]=,[RECEIVED_DATE.autoCalendar.Month]=,[RECEIVED_DATE.autoCalendar.YearMonth]=>}REF)