There is only one window of about 8 to 20 hours where you can conceive. That is the time from ovulation (an event that takes about 15 minutes) until the unfertilized egg dies.

Your fertile window is usually calculated to start 5 days before the predicted ovulation day, ovulation day, and the day after ovulation day. That is the days that his sperm can stay alive inside your body to wait for that live egg.

In order for fertilization to take place while your egg is alive, there needs to be live healthy sperm around it in your fallopian tube. After ejaculation, your partner’s sperm will swim up your cervix, uterus, up the fallopian tube to wait for your egg to be released. The sperm can stay alive there for about 3 to 5 days, in some extraordinary cases even as much as 7 days, waiting to mate with your released egg.

That is where the fertile week comes from. It is the predicted time where his sperm can stay alive to wait for your egg until the egg dies.

It is not smooth sailing for his sperm. After ejaculation there are hundreds of millions of sperm in his semen (typically 100 million to 200 million sperm per ml of semen). His semen liquifies in waves over the next 20 to 30 minutes to allow the sperm to escape. Then it has to find the cervix opening and fight its way in through your cervical mucus.

Outside your fertile week, your cervix opening is usually tightly closed and the mucus inside it is thick and unfriendly to sperm. During your fertile week, the cervix opens up and you There is an absolute slaughter of his sperm along the way. A lot of his sperm are just faulty, badly formed, unable to swim forward, or dead. Roughly 1,000 to 10,000 makes it through your cervix, and only a few hundred at most makes it to the fallopian tube where it waits for your egg to be released. In the few hours after ovulation, it may even meet your egg while they swim up your fallopian tube if you have intercourse then.

So you can see that your ability to conceive depends on accurately predict your ovulation day, and timing intercourse around that. You are basically very fertile for 3 days, fertile for another 2 days, and maybe somewhat fertile for an extra 2 days making up 7 days in every cycle. So in a typical menstrual cycle of 28 days, you are infertile for 21 days and only fertile for 7 days.

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