Calculate No of days elapsed

Hi Experts,

I am stuck on a calculation to find out no of days elapsed in a month.For eg:If i Select Jun it should show 30 and if i select Jul it should show 13.

I am using a calculation which doesn't seem to be working:

if year(ATTR([Complete Date Of MFG]))=YEAR(ATTR([Complete Date Of MFG]))

then DATEDIFF('day',ATTR([Start of month]),ATTR(TODAY()))+1

end

and if i am using max instead of ATTR then result is not coming as expected.

Start of month is also a calculated field:

if year([Complete Date Of MFG])=year(TODAY())

then DATETRUNC('month',[Complete Date Of MFG]) end

Please help

Thanks