Naegele’s rule involves a simple calculation: Add seven days to the first day of your LMP and then subtract three months. For example, if your LMP was November 1, 2017: Add seven days (November 8, 2017). Subtract three months (August 8, 2017).

The rule estimates the expected date of delivery (EDD) by adding a year, subtracting three months, and adding seven days to the origin of gestational age. The result is approximately 280 days (40 weeks) from the start of the last menstrual period.

Because few women know the exact day they ovulated or conceived, an ultrasound done in the first trimester of pregnancy has been shown to the be the most accurate way to date a pregnancy. If an ultrasound date in the first trimester differs from your LMP date by seven days or more, we would go with the ultrasound.

That’s the day you conceive. So without knowing the day of conception, how does anyone determine a due date? The most common way to calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period (LMP). And that’s how most healthcare providers do it.

First, Get a Lawyer If you even have an inkling that a child isn’t yours, whether or not the child has been born yet, speak with an attorney. An attorney can help guide you through the steps you need to take to determine paternity and go through any potential court proceedings in the future.

Researchers pawed through a host of scientific articles published around the world from 1950 through last year. The perceived “paternal discrepancy rate,” as it is called, ranges from less than 1 percent to as high as 30 percent in the various studies. Most researchers believe the rate is less than 10 percent.

To answer our first question – can you “get a refund” if you’ve paid child support for a child who is not yours? – that answer is no, because when you made those payments, you were meeting a legal obligation that you accepted when you signed an Acknowledgment of Paternity.

A non-biological father is a parent who is not related to the child by blood. Despite not being biologically related to the child, a non-biological parent can still obtain legal parental status by formally adopting the child.

Once an unwed father establishes paternity, he needs to determine his custody status. An unwed man who is legally designated as the father has the same custody rights as a married father. But if at any time they separate, the father will need to petition a court to establish custody rights.