charting your cycles and finding your fertile window can be confusing. the good news is that you are putting in the most important day the day your period starts. a period start usually coincides with the time that our ovary hormones are at there lowest when the cyst of ovulation from the last cycle has gone away and the body is just starting to pick our next cycle's egg. this is the most important date for your monitor. a period end date is much less helpful because length of cycle is affected by too many factors. i recommend continuing to do exactly what you are doing: enter the first day best guess on the last day or just let it calculate the date.
i am trying to get pregnant. the ovulation calendar needs an exact date my period ends. how do i calculate that?