Pregnancy depends upon many factors like ovulation, normal pH of vagina, normal intact uterus, normal hormonal levels and normal sperm count of your partner. Ovulation usually takes place at mid of the cycle. If you have 28 days cycle then you might ovulate after 5-6 days. So, intercourse on day 12-13-14 and 15 can lead to pregnancy if every thing is alright.
My cycle has always been that I ovulate on day 7, 8, or 9 in a 21-29 day cycle. I found this out trying to get pregnant. You can buy a $1 ovulation test kit at futuremoms.org or take your basal temperature. The day 14 is a myth. I have no idea why they tell women that.
The odds are pretty low. Most women ovulate 12-16 days into their cycle. But any sex from day 10 on is cutting it pretty close.