Due date calculator

Frequently asked questions

What is the difference between dating from LMP versus conception date?

The last menstrual period (LMP) method adds 280 days from the start of your last period, while the conception-date method adds 266 days from the estimated day of conception. Both approaches target the same endpoint; the LMP path is more commonly used because the exact conception date is often unknown.

How accurate is a calendar-based due date estimate?

Calendar estimates are useful planning benchmarks, but only about 5% of births occur exactly on the projected date. First-trimester ultrasound measurements are generally considered more precise for confirming gestational age when there is uncertainty about cycle length or conception timing.

What does "gestational week" mean and how is it counted?

Gestational age is counted from the first day of the last menstrual period, not from conception. Week 1 begins on that LMP date, so at the point of a positive pregnancy test most people are already around 4–6 weeks gestational age.

Can I use a conception date if I know it from IVF or tracking?

Yes. Selecting the conception-date option lets you enter a known fertilization or transfer date. The calculator adjusts the interval accordingly and still reports gestational age on the standard obstetric week scale.