The due date for the last menstrual period on April 16th is January 23rd of the following year. The due date can be calculated from the time of the last menstrual period. If you have a regular menstrual cycle, the due date is calculated from the first day of your last menstrual period by adding 9 or subtracting 3 to the month and adding 7 to the day. If the last menstrual period is April 16th, then the expected date of delivery is January minus 3, and the date plus 7 is the 23rd, so the expected date of delivery is January 23rd of the following year. If your menstrual cycle is irregular, you should recheck your due date during pregnancy according to the size of the fetus on the obstetric ultrasound, and recheck your due date based on the week of pregnancy as projected by the obstetric ultrasound.