AppleScript Date calculation
Maybe using a different approach will accomplish what you were looking for?

set someDate to "09/ 09 / 2019"
set theDate to date someDate
set currentDate to (current date)

set secondsBetweenDates to (theDate - currentDate)
set timeInDays to (secondsBetweenDates div days)
set timeInWeeks to (secondsBetweenDates div weeks)
set extraDays to (timeInDays mod timeInWeeks)


display dialog ((timeInWeeks as text) &amp; " Weeks &amp; " &amp; extraDays &amp; " Days Remaining Until " &amp; someDate) ¬
    buttons {"Cancel", "OK"} default button "OK"


Obviously change the value of someDate to whatever you need