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For those asking how to calculate ovulation and fertile days, here we go again.

First you need to know your cycle length before you can know your likely ovulation day. Note that a normal cycle length ranges between 21-35 days, anything below 21 days or above 35 days is abnormal, so see a doctor).

To know your cycle length (that is how many days it takes before you see your menstrual period) you start counting from the FIRST day you saw blood to the FIRST day you’ll see blood of your next period (which can be within the same month or the next month, it doesn’t matter so long as the number of days is within the normal range of 21-35 days, when you count the interval between previous & present).

If your period started on, 9th June and that of July started may be on 5th July.

If you count from 9th June to 5th July, you have 27 days, so 27 days is your cycle length. It might not be 27 days for every month but always count from the FIRST day of an existing period to FIRST day of the next one to get your cycle length.

When you can accurately calculate your cycle length, you can then be able to know when to likely ovulate and also your fertile window.

To calculate ovulation/fertile days after you have known your cycle length which can be anything between 21-35 days.

ALWAYS USE 14 as a constant factor that should be applied to know your ovulation day irrespective of the cycle length.

If the cycle length is 27 days.
You subtract 14 from 27 to know your ovulation day.


The 13th day counting from the first day your period started is likely your ovulation day (and it lasts for 24 hrs).

Your fertile window is 5 days before the ovulation day & a day after (7 days altogether).

_To illustrate better;_
If your period started on 9th June and you have already calculated your cycle length to be 27 days, applying the 14 factor to calculate ovulation (27-14=13) you are likely to ovulate on 21st June (counting 13 days from 9th June which is the first day your period started) and fertile window will be 16th, 17th, 18th, 19th & 20th & 22nd June (that is five days before ovulation day & a day after).

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