How is due date calculated?

From last menstrual period we use Naegele's rule: LMP plus 280 days (40 weeks), adjusted if your cycle is not 28 days. Conception adds 266 days; ultrasound and IVF use clinical offsets. Your provider may revise dating after early scans — treat this as an educational estimate.

How accurate is due date?

Only about 5% of babies arrive on the exact estimated due date. A range of roughly two weeks before or after is common. Irregular cycles reduce LMP accuracy. Your clinician's dating from ultrasound often overrides calendar estimates when they differ.

How is IVF due date calculated?

We add 266 days minus the embryo day (3, 5, or 6) to the transfer date, matching common clinic practice for fresh and frozen transfers. Enter the transfer type and date your clinic recorded. This is not a substitute for prenatal care or ultrasound confirmation.

Early ultrasound dating is often preferred when cycles are irregular or LMP is uncertain. Choose the ultrasound method and enter gestational age at the scan. First-trimester measurements in early pregnancy typically refine due dates more accurately than calendar math from LMP alone.

Gestational age is counted from the estimated LMP, not conception, in standard obstetric dating. We show weeks plus days from that reference to today or your chosen date. Only a small share of births occur exactly on the computed EDD.