If I am 6w4d today today (10/16/14), when was my baby conceived?

Anywhere during a 4 week window. Two weeks before to two weeks after 6 weeks and 4 days ago. If you slept with more than one man that month... you will NEED to have a DNA test done to prove who the father is. So tell them ASAP if that's the case.

Most people asking this question have slept with more than one person and are hoping to not have to tell more than one person, which simply isn't possible.