How to Calculate Your Fertile Period and Natural Family Planning

The practice of natural family planning relies on understanding your menstrual cycle so that, as a form of birth control, you can choose when or when not to have sexual intercourse with your partner. Natural family planning provides an alternative to using birth control drugs or products and is a favorable option for women who do not believe in interfering with natural processes or who prefer natural birth control based on religious grounds.

Things You'll Need

• Pen
• Annual calendar (with boxes to write in for each day of the month)
• Tissue
• Calculator
• Thermometer

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Instructions

• 1

  Write down the first day of your period on your calendar. This is day one of your cycle, and your cycle ends the day before your next period starts. Mark day one of your period in your calendar every month from now on.

• 2

  Note anything else of importance in your calendar that happens during the month before your next period arrives. For example, watch for changes in your cervical mucus, which can help you to identify when you are ovulating and are, therefore, most fertile. In the days leading up to ovulation and during, your cervical mucus will become thick, clear and stretchy when you wipe with a tissue, similar to the appearance and texture of raw egg white, so avoid intercourse during this time.

• 3

  Examine the dates on your calendar (once you have been filling it in for at least three months), so you can calculate the average length of your cycle. Add up the amount of days that each cycle has lasted in the past three to six months, depending on how long you have been keeping a calendar, then divide that by the number of months you used in the first calculation. For example, in the past six months, if your cycle lengths were as follows: 27, 27, 28, 28, 27, 28, you would add those figures together, which equals 165, then divide that by the number of months, which is six; your average cycle length would equal 27.5 days.

• 4

  Determine which days of your cycle are your most fertile by calculating when your ovaries are likely to release an egg (ovulation) and, therefore, could be fertilized by a sperm. According to Parents, a woman ovulates midway through her cycle, approximately 14 days before her next period. Now that you understand your cycle and when to expect your next period, you can subtract 14 from the date of your next due period to give you an indication of when you will be ovulating. For example, if your next period is due on December 27, you could expect to be ovulating around the time of December 13. Because a sperm can live up to five days inside your womb, NHS Choices advises that if you are trying to avoid pregnancy, you should not have intercourse with your partner seven days before the expected day of ovulation and one day afterward (a female egg can only survive for 12 to 14 hours).

• 5

  Take your body temperature every morning during your cycle, using a thermometer, and note it in your calendar to provide another method of natural family planning. After six days, you can calculate the average temperature of your body using the method given in Step 3. During the days leading up to and during ovulation, your body temperature will rise for three consecutive days. NHS Choices advises that when your temperature drops again, it is unlikely that you will be able to conceive during the rest of your cycle because ovulation would have finished when your body temperature dropped.