Calculate Infertile Days: Know When It Is Safe

Planning a pregnancy it is important to use several contraceptive methods, including being knowledgeable about your infertile days. Specifically, if you learn to calculate infertile days, you can plan a pregnancy better, including the timely use of contraceptives. Below you find a detailed guide to calculate infertile days.
At a Glance
  • Being aware of your infertile days also requires awareness of your fertile days.
  • There are several methods you can use to determining infertility: (1) ovulation test kits, (2) basal body temperature, (3) cervical mucus test, and (4) calendar method.
  • Never rely on infertility or fertility predictors alone, use at least 2 methods to calculate infertile days. This increases your changes to be right.
  • Signs and symptoms of ovulation or fertility include (1) increase in basal body temperature, (2) thicker cervical mucus, (3) tender and sore breasts, (4) light spotting in between periods, (5) increase in libido, and more.
  • If you’re using the calendar method, be consistent when taking note of the start of your period every month. Make sure you always have at least 6 months of marked cycles. Keep in mind, however, that the calendar method used to find out infertile days does not apply to those whose menstrual cycles are all under 27 days.

The Advantages of Infertility Awareness

For couples who want to get pregnant:

  • A proper conception can be planned for the soonest pregnancy possible.
  • Couples can take extra measures during fertile days to increase chances of pregnancy.
  • Couples can choose the best time to conceive according to their preferences.
  • Avoidance of unnecessary efforts during days when pregnancy is unlikely to occur.

For couples who want to delay or avoid pregnancy:

  • Couples can enjoy sexual contact without worries of any unplanned pregnancy during their infertile days.
  • One of the couples or both of them can use contraceptives accordingly and properly at the right time.
  • Couples can be aware of the days when they must abstain from unprotected sexual contact.

However, to be able to distinguish between fertile and infertile days, it will be vital to know the process that takes place in both phases. So let’s get down to the nitty-gritty.

Couple talking about unfertile days

The Pregnancy Process

Have you always thought that the pregnancy process is quite easy? Well not really. We all know that it just needs a sperm cell and egg cell to unite, right? In reality, however, there are many complicated factors required before pregnancy happens. To start, an egg cell is not always there for sperm cells to easily find it. Second, there are many factors that may affect the quality of sperm cells and even that of the egg cell. In essence, there has to be a perfect timing for the egg cell to be found and fertilized by a sperm cell. Once the fastest and strongest sperm cell penetrates an egg cell, fertilization will begin. Note: Sperm cells can live for up to 72 hours [Source: Corion Fertility Clinic].

Fertilization is typically complete in around 6 days from conception. Afterward, the fertilized egg travels from the fallopian tube down to the uterus for implantation. From fertilization, it often takes 3-4 days for the fertilized egg to travel and implant itself in the uterus to develop and grow. After a successful implantation, pregnancy hormones are released, which prevents the uterus wall from shedding (or menstruating, in other words). These are the hormones that are detected by pregnancy test kits, which is why such tests are not recommended for at least 2 weeks.

Menstrual Cycles

A monthly period or menstruation is simply a missed pregnancy. A woman’s body is designed to carry a child, hence the entire function of the uterus dedicated to preparing for it. Once an egg cell is released into the fallopian tube, the uterine walls will thicken to prepare an ideal environment for pregnancy. The egg cell will then slowly travel towards the ovary to wait for a sperm cell. When there is no sperm cell to fertilize it, the egg cell will break apart, signaling hormones to drop and start shedding the uterine wall lining. This lining is made of blood, which then becomes menstruation during the shedding process. This cycle repeats every month until a successful fertilization or pregnancy takes place.

The Stages of Ovulation

Are you now familiar with the fertilization process and the science behind it? Continue by acquainting yourself with these specific stages for more useful knowledge:


A cycle begins on the first day of bleeding, counted as day 1. Although this means that pregnancy did not happen, this phase ends by preparing the uterus yet again for a possible pregnancy. Bleeding can last for an average of 7 days but often varies per woman.

Follicular Phase

The stage when the egg cell takes time to mature and be ready for release. Typically, only one egg cell will successfully mature, unless the woman carries the genes for twins. This phase may begin around the 10th day of the cycle.


This is the phase where the egg cell is released into the fallopian tube and is ready for fertilization. In some women, this comes with a quick, sharp pain in the lower left or right abdomen where the fallopian tubes would be. This often occurs during the 14th day. Once the egg cell is released, it will take a few days for it to travel down to the uterus. After it reaches the uterus, the egg cell usually only have 24 hours before it disintegrates when fertilization does not happen [Source: American Pregnancy Association].

Luteal Phase

During this phase, the hormones create and maintain a thick uterine wall lining ideal for a fertilized egg. If fertilization occurs, this wall will not be shed. This also means there will be no menstruation. Instead, the fertilized egg will attach to it and begin to grow.

The lengths of each phase will vary per woman, which is why fertility calculation methods are based on the number of days from menstruation to the last phase. To find this out, mark your calendar or take note every time your menstrual cycle begins. The number of days will normally be different each month. This is why you will need at least 6 months of continuous marked months to get reliable figures.

Signs and Symptoms of Ovulation or Fertility

During the days when you are fertile or likely to get pregnant, you will notice the following changes:

  • An increase in basal body temperature or BBT (will require a BBT thermometer)
  • Thicker cervical mucus that is stretchy and slippery similar to a raw egg white
  • Increased sense of smell or sensitivity to odors
  • Tender and sore breasts that feel swollen
  • Light spotting in between periods
  • Libido may increase
  • Mild pelvic pain on either side from the release of an egg cell

These signs are a must for you to notice and take note of. Keep a journal or organize a note on your smartphone if possible. This will tell you which days you need to abstain from sexual contact or when you need to use contraceptives.

Methods Used in Determining Infertility

  • Ovulation Test Kits – These are home test kits that you can buy over-the-counter in most pharmacies. A typical kit needs a urine sample.
  • Basal Body Temperature – Use a BBT thermometer to take your temperature every morning soon as you wake up before getting out of bed. An abrupt increase of 0.5 to 1 degree Celsius often means an ovulation or fertile period.
  • Cervical Mucus Test – Stretch a bit of your cervical mucus between your thumb and index finger. If it can stretch for at least an inch, then you are fertile.
  • Calendar Method – a technique that uses a formula based on the shortest and longest menstrual cycle to determine fertile days. More on this below.

Keep in Mind! Do not base your infertile days on calculators and predictors alone. Use contraceptives in case you want to avoid conception by all means.

Using the Calendar Method to Calculate Infertile Days

Record your monthly period

1.) Make sure you have noted the start of each menstrual cycle for at least six continuous months. Your menstrual cycle will be the days from the first day of bleeding to the day before the next one starts.


If your period started on January 8, and then February 5, then you have a 28-day cycle for the month of January (count from January 8 to February 4).

Note: If all your cycles are below 27 days, the calendar method won’t be applicable.

2.) Using six months or more of marked cycles, find your shortest and longest cycle.


  • January – 28 days
  • February – 30 days
  • March – 26 days
  • April – 27 days
  • May – 29 days
  • June – 29 days

Shortest Cycle: 26 days

Longest Cycle: 30 days

Calculate infertile days

3.) From your shortest cycle, subtract 18.



This means your first fertile day will be on the 8th day of your cycle. So, if your period started on July 10, then your first fertile day is on July 17 (count 8 from July 10).

4.) From your longest cycle, subtract 11. For example:


This means your last fertile day will be on the 19th day of your cycle. From the example above, this will fall on July 28.

5.) Take note of these periods (8th day and 19th day). These will be your bases to predict your fertile days every month. However, considering that sperm cells can live for up to 3 days, it will be wise to add a margin of 3-4 days before the start date. You can also add a few days at the end if you want to be safe. These are the days when you should completely avoid vaginal intercourse to avoid pregnancy. If you wish to engage in any sexual activity, make sure to use some form of contraception.

What Can I Do to Avoid Conception

  • Always combine two or more calculation methods to predict both fertile and non-fertile days.
  • Use contraceptives when engaging in sexual activity during your fertile days.
  • Be diligent and consistent enough to mark your calendar each time your period starts.
  • Awareness of your fertile days also enables you to be aware of your non-fertile days.
  • Add margins before and after your fertile days to cover for borderline days.
  • If possible, involve your partner in the process to make better plans.
  • Consult with a doctor for methods that will best suit you and your partner.

It is a bittersweet truth that women often shoulder all the problems that come with an unplanned pregnancy. Every woman should be knowledgeable enough to take charge when it comes to fertility awareness. You must take care of your body, know your limits and educate yourself enough to be assertive when needed. The world wide web is a fountain of knowledge for those who know where to look. If you still feel uncertain, you can always consult with your doctor to deal with it professionally.


Calculate Infertile Days: Know When It Is Safe
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  1. This help enhance my understanding in calculating ovulation period.


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