Scan dates say im 12 weeks and 2 days pregnant but i of conceived until 11 ago is the scan based on your last period or did you conceive ago?

The scan date is typically based on the date of your last menstrual period (LMP), not the date of conception. This is because it is easier to determine the date of your LMP than the date of conception.

When you have an ultrasound scan, the sonographer will measure the length of the embryo or fetus to estimate how far along you are in your pregnancy. This measurement is called the crown-rump length (CRL). The CRL can be used to estimate the gestational age of the pregnancy, which is the number of weeks since the first day of your LMP.

In your case, the scan date says that you are 12 weeks and 2 days pregnant, but you think that you conceived only 11 weeks ago. This is possible if you had a late ovulation. Late ovulation occurs when you ovulate more than 14 days after the start of your menstrual period. If you ovulate late, the CRL of the embryo or fetus will be smaller than expected for the gestational age based on your LMP. This can lead to the sonographer estimating that you are less pregnant than you actually are.

If you are concerned about the accuracy of your scan date, you can talk to your doctor. They can help you to determine the most accurate gestational age for your pregnancy.