calculate when you're ovulating: an egg with sperm

According to fertility clinic Medfem, the best chance of conceiving is to have intercourse in the two to three days preceding ovulation and including the day of ovulation. Once ovulation has occurred the probability of pregnancy declines rapidly, and within 12 to 24 hours you won’t be able to get pregnant during that cycle. If a woman has sex on any of these three days, she has a 15-25% chance of becoming pregnant.

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.

How to track your ovulation

Work out the average length of your 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 should ovulate around day 14.

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Remember, the “fertile window” is the six days leading up to and including ovulation. The three days leading up to and including ovulation are the most fertile.

Depending on the length of your cycle, your most fertile days vary:

  • If you have 28 days between periods, ovulation typically happens on day 14 and the most fertile days are days 12, 13 and 14.
  • If you have longer cycles, say 35 days between periods, ovulation happens on day 21 and the most fertile days are days 19, 20 and 21.
  • If you have shorter cycles, say 21 days between periods, ovulation happens on day 7 and the most fertile days are days 5, 6 and 7.

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How do I know when I’m ovulating?

If you’re trying to conceive, it’s useful to observe and chart your fertility signs, so you know when you’re ovulating.

How to work out when ovulation is about to happen:

  • Keep an eye out for changes in your vaginal mucus. Around the time of ovulation, you might notice your mucus is clear, slick and slippery, like the consistency of egg white. This is the best sign of when ovulation is actually happening.
  • Use an ovulation predictor kit available from chemists.
  • Record your basal body temperature (BBT) every morning 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 there’s a rise in temperature, and when ovulation is happening.

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 the following month.