Chances of conception depends upon many factors. Usually, ovulation in ladies occur at mid of the cycle and egg after ovulation can live only for 24 hours during which fertilization is needed. Sperms that are released during intercourse can take some time to reach to fallopian tube and can live there for 5-7 days. So, intercourse at least 4 days before and 10-12 hours after ovulation can cause pregnancy. But some ladies ovulate early and some late. Under normal conditions, conception is possible at almost mid of the cycle or 2 weeks before periods for a 28 days cycle.