Sorry to bring up the past, but I'd use Token Identifiers, and not $mid() because you're only getting the first number.
I used:
[color:red]$duration($calc($duration($duration($ctime($fulldate))) - $duration($duration($ctime(March 22 1987 00:00:00),2)))))[/color]
to calculate the number of days since my birthdate.
It returns
947wks 2days 13hrs 12mins 47secs for me. We want to get the 947, so we use:
[color:blue]$gettok([/color]$duration($calc($duration($duration($ctime($fulldate))) - $duration($duration($ctime(March 22 1987 00:00:00),2))))[color:blue],1,119)[/color]
the same goes for the number of days:
[color:blue]$gettok($gettok([/color]$duration($calc($duration($duration($ctime($fulldate))) - $duration($duration($ctime(March 22 1987 00:00:00),2))))[color:blue],1,100),2,32)[/color]
which returns 2.
Which is a bit more efficient if you have more than 1 number.

alias f12 {
var %time = $duration($calc($duration($duration($ctime($fulldate))) - $duration($duration($ctime(March 22 1987 00:00:00),2)))))
echo -a $calc(7 * $gettok(%time,1,119) + $gettok($gettok(%time,1,$asc(100)),2,32))
}