A due date calculator is an online tool used to estimate the date of a baby’s birth. The user types in the first date of her last period, and the calculator adds 280 days or 40 weeks to the date. For example, if a woman’s last period began on July 7, 2017, she would have her baby on or around April 13, 2018.
Assumptions of the due date calculator
The designers of due date calculators make several assumptions. First off, they tend to assume that a woman’s menstrual cycle follows the average 28 days. Some women, of course, have menstrual cycles that are shorter or longer than that average.
The due date calculator is also designed to calculate the day exactly 40 weeks after the beginning of the woman’s last period. Normal pregnancies actually last anywhere between 38 and 42 weeks. In fact, only about five percent of women deliver their baby on the exact due date; most deliver within a week before or after the stated due date.
Due date calculators can therefore only provide an estimated date of birth for any given baby.
Features of due date calculators
Some due date calculators are very bare-bones; they provide the estimated date of birth, and that’s it. Others are more elaborate.
For example, one calculator from a popular website provides a report that includes such details as the probable date of conception and the dates covered by each trimester. Their sample report, for example, assumes a woman is giving birth on September 13, 2017. Her first trimester thus ran from December 7, 2016, to March 7, 2017. It also calculates the due dates for multiple births, since such children tend to be born earlier than singletons. Twins, for example, would probably be born around August 23, 2017.
Are there other ways to determine a due date?
Yes, there are other ways to determine a due date – but only a doctor can use most of them. For example, a doctor can administer an early ultrasound test and estimate the due date from the results. They can also measure the size of the patient’s uterus and calculate the due date from those results.
Finally, developing babies always follow a certain trajectory. Their heartbeat, for example, is typically heard between the ninth and twelfth weeks of pregnancy. A woman starts to feel her baby moving when between 16 and 22 weeks pregnant. Both the woman and her doctor can use such pregnancy milestones to calculate an estimated due date.