How to Calculate Your Fertile Window

by Jul 17, 2019

If you are trying to get pregnant, finding the fertile window is everything. Having sex within the most fertile days significantly increases the chance of getting pregnant. Our calculator at the bottom of this article finds your fertile window and helps to get prepared in advance, and so you know the best time to try.

woman

What is a fertile window?

Your fertile window is the most fertile days of a menstrual cycle. It is the few days that you are likely to get pregnant if having sex. The chance of conceiving outside the fertile window is not zero, but it is very small. So, if you really want to get pregnant, don’t miss the fertile window of every cycle!

The fertile window is the few days around your ovulation. Usually, it means 4-5 days leading to ovulation, until 24 hours after ovulation. Ovulation happens when the egg is released from the ovary, and it is ready to be fertilized by a sperm if they meet each other at this time.

The egg has a short life span. It only lives up to 24 hours after the release. Therefore, sperm must meet the egg before degradation happens. That is why there is usually only one fertile day after ovulation.

The good news is sperms could live up to 4-5 days within women’s mucus, given its good quality. So, up to 4-5 days leading to the ovulation, is generally calculated as part of a fertile window.

When am I most fertile?

Days within a fertile window don’t have an equal fertility level. Your most fertile days are the day leading to ovulation and ovulation day. These 2 days are called peak fertility.

Your Luteinizing hormone often surges during these 2 days. The ovulation predictor kits (OPKs) measure this hormone surge. However, since women’s cycles vary from month to month and woman to woman, sometimes OPK gives false-positive or false-negative results. If you notice your cycles vary greatly, you may want to see a fertility specialist.

Your chance of pregnancy is zero beyond 24 hours after ovulation as the egg degrades, and your fertility level gradually increases as you approach the ovulation day.

How does conception happen?

Conception happens when a sperm penetrates the outer layer of an egg, which will then divide and form an embryo. Good sperm, egg, and cervical mucus quality, as well as the best timing, are must-haves to ensure fast conception and healthy baby!

The fertilized egg moves down the fallopian tube to the uterus, within 4-6 days after fertilization. It then implants onto the uterus lining and grows there. You should take your pregnancy test two weeks after ovulation.

How to calculate your fertile window?

You need to calculate when you ovulate, to determine a fertile window. On average, women ovulate 14 days before the starting day of the next menstrual period, which is also the starting day of her next cycle.

To calculate this, you should note the starting date of your last menstrual period, which is considered as the beginning of your last cycle, and your average cycle length, which means how many days have passed between the starting date of your last menstrual period and the starting date of the next. Let’s follow this ovulation calculator steps below:

  • Note the starting date of your last period
  • Calculate your average cycle length
  • Ovulation day = Starting date of your last period + average cycle length – 14 days
  • Fertile window = 4 days leading to the ovulation day and ovulation day itself

 

What are the limitations of the calendar method?

Calculating the fertile window by counting calendar days is called the calendar method. However, even for women with a regular cycle, their timing varies hugely. We may not always have the same length of your menstrual cycles. We may not always ovulate 14 days before the next period.

It is no surprise that the calendar method usually takes 6 months or more of continuous logging, to get an accurate prediction.

What are some other ways to calculate a fertile window?

Basal body temperature (BBT), cervical mucus, and hormone tests are commonly used ways to calculate a fertile window.

  • BBT method looks for a 0.5F temperature increase after ovulation. Although this methodology sounds convenient, the egg only lives up to 24 hours after ovulation. You may miss the majority of the fertility window by testing BBT alone to track a fertile window.
  • The cervical mucus turns egg-white texture when we are in our fertile window. Watching mucus is a great way to pay more attention to our bodies. It is natural and non-invasive. However, it may take 3-6 months to learn the quality and change of our own mucus to know what we are looking at.
  • Hormone test is one of the most scientifically trusted ways to detect a fertile window. Testing the Estrogen and LH hormones often tells the full fertile window.

To know exactly what’s happening with your body, Mira measures the actual fertility hormones with a urine test, just like bringing the lab test to your home. Mira tracks fertility hormones continuously, and the Mira App tells you what to do to either try for or avoid a baby.

Calculate ovulation

First day of your last period

Length of your cycle

Limitations of the calendar method

Calculating fertile window by counting calendar days is called the calendar method. However, even for women with regular cycle, their timing varies hugely. We may not always have the same cycle length. We may not always ovulate 14 days before the next period. It is no surprise that calendar method usually takes 6 months or more of continuous logging, to get an accurate prediction. To know exactly what’s happening with your body, Mira measures the actual fertility hormones with a urine test, just like brining the lab test to your home. Mira tracks fertility hormones continuously, and the Mira App tells you what to do to either try for or avoid a baby.

Order Your Mira Today

Ready to easily, precisely, and automatically track your ovulation cycles? Let Mira take the guesswork out of getting pregnant, so you know exactly when to conceive.

Reserve Your Mira Today

Ready to easily, precisely, and automatically track your ovulation cycles? Let Mira take the guesswork out of getting pregnant, so you know exactly when to conceive.

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