Formula Contradiction

[Irwell]

Morning,

I created this formula (see below) yesterday and I've just realised that it's not working and I've figured out the reason... How would you change it?
=COUNTIFS('Tier 3 Tracker'!$F:$F,"<=30/09/2017",'Tier 3 Tracker'!$Z:$Z,">=12")-COUNTIF('Tier 3 Tracker'!$AT:$AT,"<30/06/2017")

Basically I want it count all those in column F, minus those in column AT then tell me how many of those that are left are over 12... (Does that make sense)

 

[inactiveuserps07]

Steve, I agree, except there seem to be variables we don't know about. For instance, if the end-of-quarter numbers are generated on the last day of the quarter OR if no new hires happen after the end of the quarter, your formula would seem to work. But if reports aren't done for the 3rd quarter until, say, October 15 and new hires were made between October 1 and October 15, the count would be off (as it will be anyway, however, if new records meet or exceed 12 during that period). I'm feeling like there are more controls to ... well, control for ... which we can't see or don't know quite yet.