Finding out the regular schedule of your menstrual cycle will help if you are trying to have a baby. Once you know the regular number of days between periods, you can figure out your ovulation cycle. The ovulation period is when conception is most likely, and this is the best time to try for a baby; this occurs near the halfway point of your menstrual cycle. From there, you can figure out the projected due date should you get pregnant during that ovulation time.
Count and track the number of days in your menstrual cycle. Mark down the days on a calendar from the first day of your menstrual period -- the first day that menstrual bleeding occurs -- to the day before the next period begins.
Divide the number of days in the menstrual cycle by half. If the menstrual cycle is 28 days, this number (14) is the last day of your three-day ovulation period.
Subtract two days from the divided number if your cycle is fewer than 28 days to get the ovulation end date; round up if the cycle is longer. For cycles shorter than 26 days or longer than 30, add/subtract three days instead of two.
Count off the weeks from the last date of the ovulation period using your calendar. Mark down the date 38 weeks after the ovulation date to get the estimated due date should conception occur in the aforementioned period.
Count 10 weeks from the ovulation end date -- the most likely day of conception -- to get the end of what would be your first trimester. Count 26 weeks for the end of the second trimester.
If your menstrual cycle is an odd number of days, round down when dividing for the ovulation date if the cycle is less than 28 days. Round up if it is more.