While sperm can survive for three of four days inside a woman, it only takes the egg between 12 and 24 hours to make its way through the fallopian tube after ovulation. The best chance of conception comes when a couple have intercourse one to two days before ovulation.

A woman typically ovulates 14 days before her period. If a woman has a regular cycle length of 28 days, she will ovulate mid-cycle - 14 days after day one of her period. If the cycle is longer, say 34 days, ovulation occurs around 20 days after day one of a period - not mid-cycle.

Using this calculation will tell you when the best chance of conception will be.

Some women know when they are ovulating from changes in their body and the way they feel. Some typical indicators are breast soreness, heavier and more opaque vaginal discharge, tightness in the abdomen.

Many others have no noticeable symptoms.

Basal body temperature (BBT)

Two days after ovulation, your temperature rises slightly - around 1/4 to 1/2 a degree. While this is not useful for that particular cycle, recording your temperature every morning for a few months can show if your cycle is regular, and help predict your best day for conception.

If you are looking for more information, there are any number of web sites dedicated to BBT tracking. Just remember that it is a useful indication rather than an exact science.

Regular intercourse

Knowing that sperm can survive inside a woman for a number of days, if a couple is having regular sex (two to three times a week) there is a good chance that there will be some sperm there to meet your egg when it arrives.

It is a myth that men should "store" their sperm by abstaining from sex. Long periods of abstinence can lead to a decrease in sperm quality. Our best advice is to have sex two or three times a week, no matter where a woman is in her cycle.