filter visually but not the underlying calculation?

Anonymous , if there is no date filter. using a date table

use today if needed

Rolling 12 Sales =
var _max = maxx(allselcted(date),date[date]) // or today()
var _min = date(year(_max), month(_max)-12,1)
return
CALCULATE(SUM(Sales[Sales Amount]),filter(date, date[date] <=_max && date[date] >=_min))

if you have a date selected and you want to show trend , then you need an independent date table

//Date1 is independent Date table, Date is joined with Table
new measure =
var _max = maxx(allselected(Date1),Date1[Date])
var _min = eomonth(_max, -12) +1
return
calculate( sum(Table[Value]), filter('Date', 'Date'[Date] >=_min && 'Date'[Date] <=_max))

Need of an Independent Date Table:https://www.youtube.com/watch?v=44fGGmg9fHI