Ovulation – How to calculate and predict when you are fertile

If you remember sex education whilst at school, the teachers always said to use protection as you can fall pregnant any time you have sex. As you grow older and start to learn more about the menstrual cycle, you find out that this is not entirely true. I myself did not realise that there is only a small chance of being able to conceive every month; I only found this out when I decided it was time to start trying for a baby.

Ways to calculate ovulation?

The first is the oldest method still used by many today which is by charting basal body temperature every morning, checking cervical mucus and paying attention to the body throughout the cycle.

The second is to use ovulation calendars that calculate it for you but this only works if you have a regular cycle.

The third is to use ovulation sticks also known as OPK’s – you either use midstream urine or collect some in a cup, dip the ovulation stick in and it will detect if you are ovulating or not.

Some people use a combination of ways to track ovulation such as charting temperature daily and using ovulation sticks. Ovulation sticks do not work for everyone and they can be very confusing. The introduction of digital ovulation predictors has been a success but they are very expensive. Digital ovulation predictors show up a smiley face when you are ovulating as opposed to ovulation sticks that show up two lines. For a ovulation stick to be positive the test line has to be as dark or darker than the control line; this causes much confusion to many people. Ovulation sticks never show an evaporation line like home pregnancy tests so if it’s negative it will stay that way.

How ovulation works?

When you start your menses this is known as cycle day 1 (CD1) if you have a regular 28 day cycle you should ovulate around CD14 but not everyone has a textbook cycle. So you may ovulate later or even earlier. It takes between 6-10 days for the egg to implant into the uterus and for the body to start producing HCG hormones that are detected by pregnancy tests. If two weeks after ovulation you start your menses again, then this is the end of your cycle and your new one starts on the day of your next period. The time in between periods is your cycle length.


25.03 – 30.03 menstruation (CD1-6)

08.04 – ovulation (CD 15)

21.04 – menstruation (end of cycle)

So the cycle length would be 27 days