Women often ask how to determine the “fertile time” or “fertile window”. They are actually asking when are they ovulating and fertile. The question is easily answered when menstrual periods arrive predictably every month. The timing of ovulation is quite uncertain if menstrual periods occur at variable, unpredictable intervals.
If menstrual periods are consistently near the average of 28 days, ovulation is occurring on or near the 14th day after the first day of full menstrual flow. If a woman experiences menstrual periods consistently every 32 days, she is ovulating on or near the 18th day after the first day of full menstrual flow. Yes, it is that simple.
Fortunately, for the woman whose cycles are variable, (e.g. 28 days one month, 35 days the next and back to 26 days in another month) there are urine ovulation testing kits readily available in stores. They are relatively easy to use, fairly reliable and usually easy to interpret. Testing should always begin well BEFORE the expected day of ovulation so that the first day(s) are negative. It is the change and positive test that helps.