The Fertile Window

The fertile window represents the days during a woman’s menstrual cycle when she is considered more fertile, meaning more likely to conceive from having unprotected intercourse.

1. When is the fertile window?

The exact answer is based on a “textbook” menstrual cycle of 28 days. Ovulation (release of the egg) occurs day 14. The fertile window begins about day 11 and ends about day 16. The peak fertility days are days 13-15. Being fertile means capable of conceiving, which is only possible around the time of ovulation.

2. When exactly is day one of the cycle?

Day 1 of the cycle is the first day of normal menstrual bleeding. It’s okay not to count slight spotting as day 1. Many women count day 1 as the first day after their bleeding has stopped. This is incorrect and can lead to improper calculation of the fertile window.

3. I have 32-day cycles. How can I determine my fertile window?

As long as the cycles are regular in timing, the fertile window can be recalculated. For every day longer than 28, add 1 day to the above numbers, and for every day shorter than 28 days, subtract one day from the fertile window numbers. For example, for a 32 day cycle, the fertile window would be days 15 to 20 and ovulation would be on day 18.

4. My cycles range from 26 to 30 days. How can I determine my fertile window?

You need to determine 2 fertile windows, one based on the shorter cycle and one based on the longer cycle and then combine them. For a 26-day cycle, the window is from days 9-14 and for a 30-day cycle, the window is from days 13-18, so for you the window is from days 9 to 18, and ovulation is between days 12 and 16.

5. I have very irregular cycles. How can I determine my fertile window?

If your menstrual cycles are irregular and unpredictable, you may not be ovulating at all. This condition should be evaluated by a gynecologist.

6. How often should we have sexual relations during the fertile window?
Ideally sexual relations should be every other day, or 3 times per week. Having intercourse every day does not improve the odds of conception, and can be rather tiring. Additionally, the peak fertility days are 13-15 (for a 28-day cycle), so sexual relations should occur at least once or twice on these peak days.

7. What is wrong with “taking my temperature?”

The Basal Body Temperature (BBT) is a well-known fertility technique, but can be misleading. About 2 days after ovulation, the body temperature rises slightly, and this can be detected. However, the first day that the temperature is elevated is also the day after the fertile window has closed. In other words, once the temperature is up, the window is closed! However, the BBT charts are helpful when trying to determine when someone has ovulated, but only after the fact.

8. How are urine ovulation kits useful and how are they potentially misleading?

The urine kits are designed to check for the presence of a hormone called LH. This hormone is normally present in very low levels, but before ovulation, there is an increase in production of this hormone, called the “LH surge.” The urine kit identifies the LH surge. This tells us that ovulation will occur from 12-36 hours later. For a 28-day cycle, the LH surge is usually on day 13.

However, if you wait for the LH surge, you have missed about half of your fertile window. This is because your body is fertile (capable of becoming pregnant) a few days before the LH surge occurs.

9. What is a computerized fertility monitor?

A device called the Clear Plan Fertility Monitor can detect the onset of the fertile window days before the standard urine ovulation kits do. The monitor is a hand-held electronic device that uses special urine test sticks which the device can read. The device checks for two hormones. One is the LH surge but it also checks for the increased estrogen production that precedes the LH surge. The combination allows for the earliest possible detection of the onset of the fertile window.

10. What if I don’t want to track any of this stuff?

If you have sexual relations about every 2-3 days when not on your period, you are already close to maximizing your chances of conceiving. However, if you generally have relations about once a week or less often because you and your partner are so busy/tired/away etc., you may be missing the “window.”

11. What else can I do to improve my chances of conceiving?

Men should avoid excessive prolonged heat or pressure in the genital area. This means reducing or eliminating Jacuzzi’s, saunas, steam rooms, intense exercise and bike riding (there are now special seats for those who must ride). Trading in jockey shorts for boxers can also help.

Women should be aware of their bodies. When the fertile window begins, there may be an increase in watery vaginal mucous production (almost like egg white). There may be an increased libido (sex drive). These signals should not be ignored, even if they occur at the “wrong” time. Female orgasm during intercourse has been shown to improve fertility by creating a small suction effect that can pull sperm into the uterus. Also, lying down on the back for 10-15 minutes after ejaculation may help improve the odds of conception. Avoid chemical agents such as gels, oils or lubricants during intercourse (water-based lubricants, used sparingly, are okay). If there is any chance of a vaginal infection being present, see a doctor right away as infections can interfere with conception.

12. For more information:

See our article called Planning for Pregnancy