Unwanted 21 Days

Ways to Track your Fertile Days and Prevent Pregnancy


Being aware of the science behind your menstrual cycles, what happens in each phase, you can easily figure out your safe period – the best time to have sex, without risking getting pregnant. Find out all that you need to know about calculating your fertile days so that you can avoid unplanned pregnancies.


Calculating your fertile days gives you a clear picture of where you are in your menstrual cycle, and which days you can have sex to avoid getting pregnant.

What is your safe period?

Also known as the unfertile period, this refers to the time in the menstrual cycle, when the chances of a woman getting pregnant are minimal. So, if you don’t want an unplanned pregnancy, then this is the time to have sex.

Biologically, there is no egg in your ovaries during this period. When you have sex during this period, there is no chance of you getting pregnant. Tracking your infertile period and limiting intercourse to these days is one of the most common ways to prevent pregnancy.

How to calculate your safe window?

Generally, ovulation occurs 14 days before the next menstrual cycle starts. An egg can get fertilised only within a short window – 4 days before and 3 days after ovulation. However, this may vary from one woman to another.

If your periods are regular, then you can easily track your ovulation days, and avoid having intercourse during these days, to prevent an unplanned pregnancy.

How to calculate fertile days in your menstrual cycle?

To calculate safe days of your pregnancy cycle, you must start by tracking your fertile days. There are several ways to do this.

Method 1: Using length of menstrual cycle to find your fertile days

If you are looking for a simple method of how to track your fertile days, then here’s a guideline for you to follow.

Length of Cycle Most fertile days of your menstrual cycle


Days 5 to 10


Days 9 to 14


Days 11 to 16


Days 16 to 21

If you want to avoid getting pregnant, then you need to avoid having intercourse on your most fertile days, based on the length of your menstrual cycle. Since menstrual cycles have varying lengths; this isn’t the most trustworthy method to use.

Method 2: Calculate your safe window based on your individual menstrual cycle lengths

If your menstrual cycle length varies from one month to another, then you can use this method to calculate your infertile days.

  • Step 1 – Start by tracking your periods for the next six months. Note down your cycle length for each month.

Let’s assume, these were your cycle lengths for the last six months.

Month Cycle Length
Month 1


Month 2


Month 3


Month 4


Month 5


Month 6


  • Step 2 – Find out your shortest cycle. In this case, the shortest cycle is 26 days. Subtract 18 from this number, which is 26 – 18 = 8. Now, note the start date of your next periods. This is your day one. Count forward using the number you got from subtracting.

Let’s say, your next cycle starts on the 1st of the coming month. In this case, you have to count 8 days forward. You will reach 8th. Note down this date.

  • Step 3 – Find out your longest cycle. In this example, the longest cycle is 30 days. Subtract 11 from it. 30 – 11 = 19.

Now, count forward from the start date of your next period (day one), using the number you got from subtracting.

Let’s say, your next cycle starts on the 1st of the coming month. In this case, you have to count 19 days forward. You will reach 19th. Note down this date.

  • Step 4 – You would have marked a window in your calendar. In this case, the window is from the 8th to 19th. The dates between the 8th to the 19th are your fertile period.

You can have unprotected sex on any date outside this window during the coming menstrual cycle and reduce your chances of getting pregnant.

If that seems plenty of work and lots of calculations, you can use the next method to track your infertile days.

Method 3: Use technology to help you track your cycle

Numerous apps help you track your menstrual cycle to calculate your fertile and infertile days. These apps provide you with the required data for your handy reference.

Keep in mind that no method is 100% safe

While these methods are reliable, they aren’t foolproof. For instance, if your periods are irregular, then you may risk getting pregnant, even if you have sex on days outside your fertile window. The success rate of these methods depends on the regularity of your periods, the calculator you use, hormonal ups and downs, and how religiously you follow it.

If you are looking for an easier and 100% safe solution for how to prevent pregnancy, then you can choose easy to use birth control pills and contraceptives. These are highly reliable and free from meticulous and complicated calculations and planning.


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