Hello Rachel Thanks for your query. Actually during a menstrual period, the gap between ovulation and next period is fixed, but not the gap between start of period and ovulation. For example , if your period was 29th April, reasonably speaking, your calculation of ovulation is correct, but if the next period is irregular, then the ovulation would have occured 14 days before period, not 14 days after it. Also, within each cycle, the days of ovulation are variable. So just based on that , do not plan a pregnancy. Keep track of your basal body temperature, changes in cervical mucus etc . to track ovulation. You can seek help of a gynecologist for follicular monitoring ifyou are really desperate to have a baby. Take care.