Let's say I have these two dates:

4/5/2013
1/9/2015

I want to calculate how many bi-weekly pay periods there are between those two dates INCLUDING the first date, but NOT including the second date. So far I have used the good ol' count the days on the calendar, but now I have dates that are much earlier and thought it would be much more efficient to use a formula instead of counting manually.

I haven't really used formulas for dates before, so I don't really know where to start. Any help is appreciated!!