When a woman discovers she is pregnant, her estimated due date may be one of the first things that pops into her head. Although it is possible for women to calculate this date manually, pregnancy calculators are typically easier to use and offer the information more quickly.
Function
Pregnancy fertilization calculators predict an estimated due date. These calculators use the date of the last menstrual period, date of ovulation, average length of menstrual cycle and whether it is a first pregnancy to provide this information. Some pregnancy calculators also estimate a date of conception from an estimated due date.
Types
Many types of pregnancy calculators are available. Most calculators that are available online use the 280-day method to calculate an estimated due date. This involves simply adding 280 days to the first day of the woman's last menstrual period to get the due date. Other online pregnancy calculators use Naegele's method or Wood's method to calculate estimated due dates. Naegele's method adds seven days, subtracts three months and then adds one year. Wood's method adds one year to the date of the last menstrual cycle, then subtracts two months and two weeks and adds the number of days the woman's menstrual cycle varies. Calculators using Naegele's method or Wood's method may adjust the estimated due date if it is a first pregnancy.
Benefits
Many pregnant women don't have their first prenatal appointment until they are at least eight weeks pregnant, according to the American Pregnancy Association. Since waiting this long before getting an estimated due date is undesirable for many women, pregnancy calculators are a good way for pregnant women to obtain this information sooner.
Considerations
Since pregnancy calculators use averages to predict due dates, they are not always accurate. Pregnant women should consider using multiple pregnancy calculators or methods to predict their due dates to get a more accurate range of their baby's arrival. A doctor or midwife may use an ultrasound or palpate the abdomen to find out the size of the uterus to confirm or adjust the estimated due date obtained by a pregnancy calculator.
Misconceptions
Contrary to what some believe, most babies are not born on their due dates. In fact, Marjorie Greenfield, M.D., a contributor to DrSpock.com, points out that while 80 percent of babies are born within two weeks of their due dates, only 5 percent are actually born on the exact due date. Pregnant women should not rely too much on the specific due date and view it as an estimate instead.
