Women’s guide to getting the timing right

Apart from being healthy, what might help you get pregnant? Sex! (Or intercourse at the right time, to be technical about it.)

The best time to try and conceive is during the ‘fertile window’ of the menstrual cycle; this is different for different women.

The fertile window

We’re talking about the days in a woman’s menstrual cycle when pregnancy is possible. Pregnancy is technically only possible during the five days before ovulation through to the day of ovulation.

These six days are the ‘fertile window’ in a woman’s cycle, and reflect the lifespan of sperm (5 days) and the lifespan of the ovum (24 hours).

If a woman has sex six or more days before she ovulates, the chance she will get pregnant is virtually zero. If she has sex five days before she ovulates, her probability of pregnancy is about 10%.

The probability of pregnancy rises steadily until the two days before and including the day of ovulation.

At the end of the ‘fertile window’, the probability of pregnancy declines rapidly and by 12-24 hours after she ovulates, a woman is no longer able to get pregnant during that cycle.

For those women who are not aware of their ‘fertile window’ or when they ovulate, sexual intercourse is recommended every 2 to 3 days to help optimise their chance of conceiving.

The likelihood of actually becoming pregnant is dramatically increased if you have intercourse in the three days leading up to and including ovulation.

If a woman has sex on any of these three days, she has a 27-33% chance of becoming pregnant.

Adapted from data by Wilcox, A.J. et al. NEJM (1995) 333:1517

Myth conception

The myth:

"The best time to try to conceive is day 14 of your menstrual cycle. "

The truth:

The only time a woman can conceive is during the ‘fertile window’ of the menstrual cycle. This window will vary depending on the individual’s cycle, however timing intercourse in the 6 days leading up to and including ovulation is the window with highest chance of conception.

What is ovulation?

Ovulation is when a mature egg is released from the ovary, moves down the fallopian tube, and is available in the fallopian tube to be fertilised.

Tracking your ovulation

  • Work out the length of your average menstrual cycle. Day one is the first day of the menstrual period and the last day is the day before the next period begins.
  • Ovulation happens about two weeks before the next expected period. So if your average menstrual cycle is 28 days, you ovulate around day 14.
  • Remember the ‘fertile window’ is the six days leading up to and including ovulation.

If you have a 28 day cycle, with ovulation typically happening on day 14, the ‘fertile window’ starts on day 12. If you have longer cycles, say 35 days between periods and ovulation happens on day 21, the ‘fertile window’ starts on day 19. If you have very short cycles, say 21 days and ovulation happens on day 7, your ‘fertile window’ would start on day 5.

Fertile window calculator for different cycle lengths

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  • Fertile window
  • Most fertile time
  • Predicted ovulation day

Your fertile window is between days:

9 & 14

Your most fertile time is between days:

12 & 14

Your predicted ovulation day is:

14

How do you know you’re ovulating?

Women’s cycles can vary and are not always as regular as clockwork, so to know that you are ovulating and on which day of your cycle you are ovulating, observe your fertility signs throughout your cycle and record them on a chart.

The most accurate methods of working out when ovulation is about to occur are:

  • Keep an eye out for changes in your mucus. Around the time of ovulation, you may notice your vagina’s mucus is clear, slick and slippery, the consistency of egg white. This is the best sign of when ovulation is actually happening. It’s prime time for action.
  • Use an ovulation predictor kit. You can start testing with your ovulation predictor kit a few days before your estimated day of ovulation. Subtract 17 days from your average cycle length and start testing from this day of your cycle, e.g. if you have a 28 day cycle, you would start testing from day 11. A positive result means you are going to ovulate within the next 24 to 36 hours.
  • Record your basal body temperature (BBT) each day before getting out of bed. A special basal body temperature thermometer will ensure accurate measurement. Your BBT rises about half a degree Celsius after ovulation has occurred. By charting your temperature, it’s easy to see when the rise in temperature and ovulation happens. This can help you work out your own pattern of ovulation. However, because at that stage ovulation has already passed, it does not help you pinpoint the fertile window but may guide you for next month.
  • Use the ovulation calculator on this site. If you know the date of your last period, the length of your cycle and your cycle is regular, this will identify your ‘fertile window’ and predicted ovulation date.

Fertility Factors: Timing

When you’re trying to get pregnant, timing is everything, as Justine and Mick are well aware.

Read the transcript

Ovulation calculator

Please select the first day of your last menstrual period:

Usual number of days in your cycle:

Other factors affecting women's fertilityMen and fertility