My due date is July 21st what month and date did I get pregnant

We can't tell you an exact date, it all depends on when you ovulated.

Is this a question about paternity? If so, the only way to know who the father is is a paternity test after the baby is born. Everything else is only a guess.

If your due date is July 21, you most likely conceived on or about October 28.

If this is a question about paternity, a DNA test will have to be done after the birth of the baby.