How to use COUNTIF formula to calculate open/closed issues

I'm attempting to build an Issue Register for projects I work on; I've got some formulas to track how many issues were opened or closed on any day, but I also want to keep a running tally of issues opened and closed over a 30 day period.
I can't figure out how to do it!

I have my data range for issues opened on a day and closed on a day, and I have my running 30 days, how do I calculate open and closed for a given 30 day period?

Any help appreciated!

If I've understood - you could combine 2 SUMIFs, eg:

=SUMIF($J$7:$J$307,">"&$N7-30,K$7:K$307)-SUMIF($J$7:$J$307,">"&$N7,K$7:K$307)
copied across matrix O7:P43

or you could use a single SUMPRODUCT - I'd be inclined to use the SUMIFs myself.

(note the upload is seemingly running on 1904 date system - ie J7 is showing as 13-Aug-2014 rather than 12-Aug-2010)