What is the latest date i could have conceived if my periods are regular and come around the same time each month. my last period was may 3.?

Today: It ultimately depends on when you ovulated. If you haven't had a period since may, you need to see your obgyn to see if you are pregnant already. If not, he/she can help figure out why your period is so late. Good luck.

It depends: If your cycle length is 28-30 days, that is, the number of days from the first day of your period until the day before the first day of your next period, then you can conceive on d14 until d17. The exact last day depends on each cycle length, which are always a few days different. When you conceive, your next period doesn't arrive, so you never know exactly.