Last menstrual period: February 12 — What is the estimated due date?
Apr 28, 2022
Source: Cainiu Health
Dr. Chen Zhe
Introduction
If your menstrual cycle is typically very regular and your last menstrual period (LMP) began on February 12, your estimated due date (EDD) would be around November 19, with delivery likely occurring up to one week earlier or later. The EDD is generally calculated by adding 9 months (or subtracting 3 months) to the month of the first day of the LMP and adding 7 days to the date. However, if your menstrual cycle is shorter or longer than average, the EDD should instead be determined based on the gestational age established during the first ultrasound examination that detects fetal cardiac activity.
If your menstrual cycles are typically very regular and your last menstrual period (LMP) began on February 12, your estimated due date (EDD) would be approximately November 19, with delivery likely occurring up to one week earlier or later.
Generally, the EDD is calculated from the first day of the last menstrual period. A full-term pregnancy lasts about 40 weeks, and gestational months are calculated as 28-day intervals—i.e., four weeks per gestational month. Thus, the EDD falls nine calendar months and seven days after the LMP. For example, if the LMP was February 12, adding nine months yields November; adding seven days to the 12th gives the 19th—hence, the EDD is November 19. However, if the LMP was April 28, adding nine months would exceed December; instead, subtract three months to arrive at January, and add seven days to the 28th, yielding 35 days. Since January has only 31 days, the EDD becomes February 4.
Therefore, the standard method for calculating the EDD is to add nine months (or subtract three months, if necessary) to the month of the LMP’s first day, and add seven days to the date—assuming a typical menstrual cycle length of 28–30 days. If the cycle is significantly shorter or longer, the EDD should be adjusted based on the gestational age determined by the first ultrasound examination that visualizes the fetal heartbeat. The ultrasound-determined gestational age is used to retrocalculate the likely date of the LMP, which then serves as the basis for recalculating the EDD.
