Your baby’s due date is usually estimated as about 40 weeks (or 280 days) from the first day of your last menstrual period (LMP). This is often called Naegele’s rule and is what most clinicians start from, then adjust if needed after an early‑pregnancy ultrasound.

Quick‑and‑easy way to estimate

If you tell me the first day of your last period , I can do the math for you in text. Generally:

  • Start with the first day of your last menstrual period.
  • Add 40 weeks (280 days) to that date.
  • Many calculators also let you enter conception date instead, which then uses 38 weeks (266 days) from that date.

For example, if your LMP was January 1 , adding 280 days would put your estimated due date around October 8 (not on the dot for everyone).

When the “official” due date is set

  • Ob‑gyns often confirm the due date after your first‑trimester ultrasound , which may nudge it a few days earlier or later depending on fetal measurements.
  • If you used IVF or know your exact conception/trans‑fer date , the due date is typically calculated as 266 days from that date.

Forum‑style “when is my baby due?” pattern

On parenting forums, people usually phrase it like:

  • “LMP: Jan 10 → when is my baby due?”
  • “Conceived around Feb 8 → EDD?”

If you want, reply with your LMP (first day of last period) or conception/transfer date and cycle length , and I’ll walk through the exact calculation and show what the due‑date window is for you specifically.