If my due date is 09/13/2010 what day did I have sex on

Sometime in Oct, due dates are estimates based on your last period and size of baby.

There is no way to determine really an exact due date, it is just a estimate there is no way to know an exact sex date ( of course you should know and normally it really does mot matter unless you where having sex with more than one person during that same period.

In that case you will have to wait till baby is born and do a DNA test

Well this is interesting! My child is due 9/12/10 and I can tell you according to what my doctor told me. Conception had to have occurred between 06DEC09 through 21DEC09.

Congratulations!

No two women are the same. Unless you know the exact day that you ovulated, then there's no way to know for sure when you conceived.

Like Chuck said, if you had sex with more then one person and you're wondering who the father is, you'll have to wait until the baby is born and get a DNA test done.