One of the most common questions you'll hear when you're pregnant is, "When are you due?" Most likely, your prenatal care provider gave you a specific day, which you circled on your calendar.
But like most questions about life and about children, the answer is usually more complicated than that.
Our language about due dates reflects our need for things to be on time. Even the baby is considered "early" or "late." We have such a social stigma around being late, but due dates are estimations, not deadlines. But because most due dates (bills, library books) are deadlines, we tend to project that framework onto birth. People who tell their family and friends a due date may have to endure 50 calls a day asking, "is the baby here YET?" for an extra week.
But babies are not library books--no one's going to charge your baby an overdue fine. We'd prefer not to see babies come very early or late, but most babies come within a window of 2-3 weeks on either side of the due date--right on time.
Most doctors use Naegele's Rule, which is where we get the 40 week due date. Those fun little due date wheels usually follow Naegele's Rule.
The Wood's Method, sometimes called Nicol's Rule, is based on research and reflects the following important points:
All that said, here's a fairly comprehensive, queer-friendly, IVF-inclusive due date calculator. I'm pretty proud as I did most of the coding and math myself!