You are here
Usually it's between 16 and 20 weeks, but with my son I was able to find out when I was only 13 weeks pregnant.
Between 18-20 weeks when you go in for the ultrasound that measures the baby and checks for all the vital organs, halves of the brain, development, etc. They can do a gender reading at that point (if baby is cooperating). It's not the purpose of that ultrasound, so you may have to ask them to check the sex for you. My doctor told me that the sex has nothing to do with the medicine and science of your baby's development and you have to request it if you want to know.
I found out at 20 weeks, i had to wait till then, and at 30 weeks he is still a boy, the say you should wait till then so you can be sure.