When’s the best time to try to conceive baby? During her mid-cycle 16 days before her period? Her period was on July 17th.?

The answer by Pippin tells it all - there is never certainty within a day or three as to the best time. And always bear in mind that one or other of you might have fertility problems. If no joy within a year or so, both of you should visit the doctor.

Nobody here can say wxactly when she is fertile. Most women ovulate ABOUT 14 days before the first day of the next period, but there can be several days variation either way. So 16 days before her period would probably be a fertile day -- but not necessarily.

If you can't track her ovulation more reliably (with physical signs or a predictor kit), just having sex every 2-3 days from the end of her period onward should hit her fertile days without particularly trying or timing anything.