If you have intercourse and ejaculate on the day before the onset of menstruation, you will not get pregnant if you have a regular menstrual cycle. Ovulation occurs 14 days before the next menstrual period. If a woman’s menstrual cycle is regular, the chances of conception are higher if she has intercourse during ovulation, or if she has intercourse every other day for 2-3 days before and after ovulation. However, a woman’s ovulation period may be altered by many factors. If the menstrual cycle is irregular, it is not possible to determine the ovulation period as well as the safe period, so it is possible to have a very low chance of getting pregnant on the day before your period. If your period starts the day after intercourse, you are not pregnant. However, if your period is delayed after intercourse, you should consider applying a pregnancy test to determine if you are pregnant. It is advisable to use a reliable method of contraception, such as condoms or the short-acting pill, rather than unprotected intercourse.