Hi, and thanks for your medical question on eHealth forum!
If you have been trying to conceive for a year, it is time you saw an infertility specialist. One can calculate the date (approximate) by subtracting 14 from the average duration of cycle. So in a 28 day cycle the ovulation occurs on 14th day from start of menses, in a 30 day cycle the ovulation will occur on (30-14=16) 16th day of the cycle. In your case, you would be ovulating anytime between Day 13 to Day 18.
The day is counted from the first day of the period. 2-3 days before this day to 2-3 days after the day is the most fertile period. Having intercourse during this time can result in pregnancy. Keep an eye for these days and try. Please also consult an infertility specialist and undergo a few tests with your partner to know if everything is fine with both of you. Hope this helps. Take care!