Understanding Your Menstrual Cycle Length & Ovulation

Question
Hi.  I have been trying to conceive for 8 months now and starting to get little frustrated. I thought my cycle is 28 days but when I downloaded the fertility software that calculate your cycle, it says 25 days.  Last 3 months of dates are:

5/29
6/22
7/24
8/18

when I add the days and devided by 3, it shows 28. 28day cycle and 25 day cycle ovulation differs by a WEEK and if I have been aiming for the wrong week, I really need to know.  Now I'm confused and unclear what my real cycle is.  I will start using ovulation predictor kit but not sure what day of the cycle I should start.
The software is predicting the next period starts on 9/12 and ovultion between 9/19-21. Is this correct?

Would you please help?

Thanks!


Answer
If you have a normal 28 day cycle, ovulation occurs on cycle day #14. However, if you have a cycle that is longer or shorter than 28 days, ovulation occurs 14 days BEFORE the first day of your next period. If  the first day of your period in May was 5/29, and the next period started on 6/22, then you had a 25 day cycle and ovulated on June 8  (fourteen days before 6/22)(cycle day #11). If your next period started on July 24, then you had a 33 day cycle and ovulated on July 10 (fourteen days before your period began). That was cycle day #19. If your period in August was August 18, then ovulation (before that) occurred on August 4 which was cycle day #12. It appears that you are ovulating around cycle day #11-14 each month. (Ignore the long cycle). Therefore, I would concentrate on having sex on cycle day #12-16 each month. You can purchase an ovulation predictor kit from the pharmacy to further pinpoint the exact day of ovulation. Don't use the software. I doubt that you are ovulating as early as cycle day #8.