Fertility NZ is a registered charity dedicated to providing information, support and advocacy to people experiencing fertility issues.

Timing of Sex

Timing sex for conception - at a glance

  • Identifying ovulation is the most important knowledge you can have when trying to conceive
  • The best time to attempt conception is when a woman’s cervical mucus is wet, slippery and of egg white consistency, usually over a 2–3-day period immediately before ovulation
  • Timing of sex relative to ovulation is vital
  • As sperm can live for up to 3–5 days in good quality mucus it is best to try and have intercourse in the 2–3 days preceding and on the day of egg release (ovulation)
  • Couples who have intercourse every one to three days around the time of ovulation, and do not have any diagnosed fertility issues, do not need to time intercourse specifically and this may be detrimental
  • Other tools such as temperature recording and ovulation kits can be of some use, but use with caution as they identify ovulation, and the ideal time for conception is prior to ovulation.  When they give it a positive result, the fertile window is nearly over
  • Don’t save sperm - fresh sperm is better than aged.  Ejaculation at least every three days is recommended


Intercourse timing and frequency relative to ovulation is possibly the most important factor affecting the chances of conception. It is also the element over which couples trying to conceive have the greatest degree of control.

Couples who are aware of their fertile time and have intercourse during this time become pregnant more quickly.  Having sex during the fertile window also makes it easier for couples and their healthcare provider to decide whether not becoming pregnant is likely to be due to infertility rather than poor timing.

The ‘fertile window’ is determined by the lifespan of the sperm in the female reproductive tract and the life of the egg once it has been released at ovulation. Sperm live up to 3–5 days and the egg survives for 12–24 hours.  In fact, there is evidence that egg quality declines after 6–12 hours after ovulation, meaning the fertile window is shorter than commonly thought.  In this regard, it is imperative to have sex prior to ovulation, so there are sperm available when the egg is released.   Based on studies, the maximum fertile window has been determined to include the day of ovulation and the five days preceding ovulation. The most probable days for intercourse to result in pregnancy are 1 or 2 days before ovulation. 

The currently available evidence suggests that methods that prospectively identify the window of fertility are more effective than calendar calculations or basal body temperatures, for optimal timing of intercourse. These include fertility charting of vaginal discharge and using commercially available fertility monitors.  However, caution is advised when relying on urinary LH detection kits alone. The quality of cervical mucus falls rapidly as progesterone rises in response to the LH surge. Hence by the time the LH is detected by urinary ovulation kits, the cervical mucus quality may have already declined in most women.  It is the ‘ovulatory’ type mucus which enables the sperm to enter the uterus and thus reach the egg.

The best time to attempt conception is when a woman’s cervical mucus is wet, slippery and of egg white consistency, usually over a 2–3 day period. The last day of this fertile type mucus is usually the day of ovulation and should be followed by a temperature rise. The temperature rise confirms that ovulation has taken place. As sperm can live for up to 3–5 days it is best to try and have intercourse in the 2–3 days preceding and on the day of egg release (ovulation).

Basal temperatures

Recording temperature is a retrospective tool to help understand your cycle, as it is important to have sperm already present when the egg is released – it will be too late once the temperature rise is detected. 

Your temperature readings confirm whether you have ovulated.   Your temperature rises because the ovaries switch from making estrogen to progesterone after ovulation.   You will have relatively low temperatures from the time of your period until you ovulate. Ovulation will then cause a rise of about 0.2°C. The beginning of the rise in temperature signifies ovulation. Once you have ovulated, the temperatures remain high until there is a dip just before your next period. Temperatures must be taken under the tongue with a digital thermometer first thing in the morning before getting out of bed. It is also important to note that your temperature may fluctuate in response to other factors, such as infections.