Easy Date Incrementation in a formula

Hi guys,
I run an analysis sheet each month where the dates in the formula increase each month to give me a years figure in each cell.

For instance, I would get data that shows my current fleet levels, and I need to pull data out to give me totals of those drivers that have been with us between 12 and 23 Months. I currently use a formula as below:
=COUNTIFS('National Working Fleet'!$E:$E,">=01/06/2014",'National Working Fleet'!$E:$E,"<=31/05/2015",'National Working Fleet'!$F:$F,"",'National Working Fleet'!$G:$G,"On-Circuit").

In the row below I would change the dates in the formula to give me those that have worked for us between 24 and 35 months, using the formula:
=COUNTIFS('National Working Fleet'!$E:$E,">=01/06/2013",'National Working Fleet'!$E:$E,"<=31/05/2014",'National Working Fleet'!$F:$F,"",'National Working Fleet'!$G:$G,"On-Circuit").

What I am looking to do is find an easy way of incrementing the dates by one month each month, rather than have to manually change each cells formula.

Is there an extra bit of formula I can add (and where can I add it), so that I can just fill downwards from one cell and it changes accordingly?

Many thanks in anticipation

Martin