What will be my wife's ovulation period?

We are trying 2 concieve 4 more than a year now. My wife's last 3 months menstrual cycle dates r Mar 7th, Apr 12th & May 15th. Before these 3 months her cycle was regular for 32 days i.e Oct 31st 2012, Dec 2nd, Jan 3rd 2013, Feb 4th. But now 4 the past 3 months her cycle has increased more than 32 days. Please let me know what will b her ovulation period this month. Serious answers please.