Some sperm can reach an egg within 30 minutes and then possibly penetrate the egg in order to fertilize it. Sperm can live in the female reproductive tract for about 48 to 72 hours and can cause fertilization at any point during that time frame, according to New Health Guide.
Healthy men produce about 40 to 150 million sperm per each ejaculation. Only several hundred of these sperm are able to get near the woman's egg, according to New Health Guide, because of the natural barriers that exist within the woman's reproductive tract. If fertilization occurs, it is caused by whichever sperm first reaches and then penetrates the egg.