Generally you ovulate mid cycle- based on a 28-day cycle. If you're cycles are not normal, i.e. you don't have the same regular cycle each month, then it's harder to tell when you ovulate. In that case use ovulation prediction kits to help determine when you ovulate. In general (textbook) based on a 28 day menstrual cycle you will ovulate about the 14th day...then you should get your period 14 days later. The egg survives for about 12 to 24 hours . So it's within this time that the sperm has to meet egg. Your fertility window is about 2 to 3 days before you ovulate. So you could essentially have intercourse two days before you ovulate and get pregnant. Sperm lives for about 48 to 72 hours. Girls sperm live longer than boy sperms, but they are slower swimmers.
So about day 10 or 11 of your cycle to day 14 you could get pregnant, assuming you have regular menstrual cycles and you cycle comes every 28 days.
There is no time that you will definitely get pg. If it were that easy, we wouldn't be here ttc for so long. A normal, healthy couple has about a 20% chance of conceiving each cycle. Knowing your cycle will help determine when you o. All women are different and every cycle is different. Try using opks to narrow down your personal fertility window. Good luck!