Ultrasound Due Date Calculator

Use the age the ultrasound measured, often labeled GA by US or GA by CRL. Do not use the age worked out from your last period, often labeled GA by LMP or from dates. Report labels vary between clinics, so ask your sonographer if you are not sure. If your report only shows a due date, enter it in the due date option of the gestational age calculator.

Sometimes. ACOG advises keeping the LMP due date when the scan is close to it, and using the scan due date when the gap is larger than a set number of days. That number depends on how far along you were at the scan: more than 5 days up to 8 weeks 6 days, more than 7 days from 9 weeks to 15 weeks 6 days, more than 10 days from 16 weeks to 21 weeks 6 days, more than 14 days from 22 weeks to 27 weeks 6 days, and more than 21 days from 28 weeks. Add your last period date above to see where your own scan falls. For a plain-English walkthrough of why dating scans move due dates, see gestational age vs fetal age.

A first trimester ultrasound is considered the most accurate way to date a pregnancy, because babies are most similar in size early on. A last period date works well when your cycle is regular and you are sure of the date, but it can be off if you ovulated earlier or later than day 14. When the two agree closely, providers usually keep the last period date.

Usually not. ACOG advises that once your due date is set from your first reliable dating scan, later changes should be rare. Scans later in pregnancy check growth, and a baby measuring a little ahead or behind then is normal variation, not a new due date. If your only scan was late in pregnancy, ask your provider how your due date was set.

Subtract 266 days from the ultrasound due date. The calculator shows a window of about three days either side, because conception timing varies. If that window does not match the date you expected, that is common. Sperm can survive for up to 5 days, so sex earlier in the week can still lead to a later conception. To work it out from other dates, use the conception date calculator.

Pregnancies from IVF are normally dated from the embryo transfer date, which is more precise than a last period date. Ask your clinic how they use scans alongside that date. Use the IVF due date calculator.

It is an estimate. A first trimester scan gives the most reliable dating, and accuracy drops the later in pregnancy the scan is done, because babies grow at different rates. Full term runs from 39 weeks 0 days to 40 weeks 6 days, and most babies arrive somewhere between 37 and 42 weeks.