How Accurate Is A Pregnancy Date Calculator?

When a woman learns she is pregnant, the very next question she has is usually "When am I due?" Expectant mothers need to have an "end date" in mind, a date for them to work towards. That also helps her know how far along she is, and at what stage the development of the baby is at. The secret is to check with a pregnancy date calculator.

It is common for an expectant mother go to an online pregnancy date calculator to figure out these things. If she knows the first date of her last monthly menstrual period, she can input that date and it will calculate for her when her due date is. Or she can figure it out by hand, using a calendar to count forward 40 weeks from her last period. Or she can wait until her first visit with her midwife or doctor, and they will be happy to figure out her due date, often using a handheld calculation wheel as a pregnancy date calculator.

Should I Trust The Due Date I'm Given?

As any woman who talks to friends knows, the date is not precise. It is not uncommon to have the date modified. How many times have you talked to a pregnant friend who says, "well, they said my due date was March first, but today my doctor says that I'm probably due February 22rd…" or something like that. Pregnancy due dates change based on what information the doctor or midwife uses to determine the date. If the baby isn't growing at a rate that agrees with what is expected, the doctor can second guess the due date, and sometimes tell the mother to be prepared for a baby earlier than she thought it would arrive.

What Affects The Accuracy Of Pregnancy Date Calculators?

Since most pregnancy date calculators use the first date of the last menstrual period from which to approximate the due date, if that date is faulty, the due date will be off, as well. Some women have longer cycles than the average of 28 days. If the woman's cycle is longer than 28 days, the woman got pregnant later than the norm. Alternately, if her cycle is shorter than 28 days, she got pregnant sooner. Many women know how long her cycle is, but others have no clue, or have an irregular cycle. In the case of a woman with an irregular cycle, she wouldn't be able to use her date of last period to input in her pregnancy due date calculator.

Though pregnancy date calculators can tell a mother approximately when her baby will come, only 5% of babies are actually born on their due date. That means 95% of them come another day, with the vast majority of them arriving within the two weeks before or after the due date. Anything within that month's time is considered "on time," and unless the baby is earlier or later, generally the doctor or midwife – and mother! - has nothing to worry about.