I'm actually not sure how many days my luteal phase is. How would I go about working that out?
You'd count the days from when you ovulate to when you get your period. The 'average' is 15 days from ovulating to the day you get your your period, which makes a 14 day luteal phase. I agree with trill, cycle length doesn't matter so much if you have a good LP. Like I said before, mine was always off and was anywhere between 10-15 days.