One of the first questions on every expectant parent's mind is, "When will the baby arrive?" Knowing your estimated due date (EDD) helps you prepare for the baby's arrival, schedule prenatal appointments, and track weekly progress. While only a small fraction of babies arrive exactly on schedule, a reliable due date is a critical guide.
Depending on your pregnancy starting point, the tool uses three distinct calculation methods: - Last Menstrual Period (LMP): The standard medical method. Since the exact date of fertilization is often unknown, doctors add 280 days (40 weeks) to the first day of your last period. - Conception Date: If you tracked ovulation or used an ovulation test, you can calculate from the date of conception. This method adds 266 days (38 weeks) to the conception date. - IVF Embryo Transfer: For IVF pregnancies, the due date is calculated by adding 266 days to the transfer date and subtracting the age of the embryo (typically 3 or 5 days).
To track weekly developmental details, check out our gestational timeline tracker. To log recommended pregnancy weight gain, visit our gestational weight gain targets helper.
You might notice that the LMP method assumes a 40-week pregnancy, whereas the conception method assumes 38 weeks.
This difference of two weeks represents the phase between the start of your period and ovulation. During these first two weeks of an LMP-based timeline, you are not actually pregnant yet. However, this clinical convention is used globally to standardize medical charting.
To identify your likely fertilization day, see our estimated conception date finder. For checking calendar day spans, use our day difference counter.
While mathematical calculations provide a solid estimate, your doctor may adjust your official due date after your first trimester ultrasound.
An early ultrasound measures the crown-rump length of the fetus, which is a highly accurate way to assess gestational age in the first 12 weeks of development. If the ultrasound estimate differs from your LMP estimate by more than a few days, the ultrasound date is typically used as the official clinical standard.
Additionally, standard mathematical cycle models assume a regular cycle length. If your cycle is regularly irregular, or if you became pregnant shortly after discontinuing oral contraceptives, estimating due dates using LMP alone is much less reliable, making early ultrasound tracking the primary standard for defining your gestational milestones.
To check clock durations between dates, visit our time duration calculator. For standard arithmetic checks, try our everyday daily math helper.
Suppose the first day of your last menstrual period was January 15, 2026.
Using the standard LMP calculation method: - Add 280 days to January 15, 2026.
- 280 days is exactly 40 weeks. - Adding 40 weeks to Jan 15 results in an estimated due date of October 22, 2026.
This means the baby's birth is projected for late October. The actual delivery will likely occur within a week or two of this date.