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Fertile period calculator

Allows patients to calculate their fertile period.

What is a fertile period?

You're more likely to become pregnant in any particular month if you have intercourse during your most fertile period. Your fertile period starts about 3 days before ovulation, and ends about 1-2 days after it. This is because sperm can survive in the womb and fallopian tubes for three to four days and occasionally as long as a week, and the egg can live for 24 to 48 hours after being released. For pregnancy to occur, sperm must reach the egg within 12 - 24 hours of release.

The average monthly cycle (from the first day of one period to the first day of the next) is 28 days. Many women have shorter or longer cycles, varying in length from one cycle to another, are also completely normal.

Ovulation usually occurs about two weeks prior to the next period. For example, in a 28 day cycle ovulation usually occurs around day 14. While in a 21 day cycle ovulation will occur around day 7, and in 35 day cycle ovulation will occur around day 21.

Researchers from Australia surveyed 204 infertile women at two assisted reproductive technology centers in Melbourne, Australia. They found only 13 percent of the women could correctly identify the specific days of the menstrual cycle, just before and during ovulation, when they could become pregnant. (Journal of Advanced Nursing, 2012)

Calculating the fertile period

If your cycles are regular, you may be able to determine your fertile period from using the calculator below.

Length of cycle:

Fertile Period:

Please discuss with your specialist if your cycle is shorter than 21 days or longer than 35 days.

Other methods used to predict ovulation

  • Some women experience a small amount of spotting or abdominal pain at ovulation. Ovulation pain may last anywhere from a few minutes to a day.
  • Do it your self ovulation kit which you can buy it over the counter from drug stores. These are very popular, can be used at home and allow you to predict, with great accuracy, your most fertile, Thes ovulation kit work by measuring the LH surge in an early morning urine sample. A surge of LH is a key indicator that ovulation is about to occur, usually within 12 – 48 hours. Once the surge is detected, intercourse over the next day or two has the most chance of resulting in conception.
  • Checking for changes in your cervical mucus. As your cycle progresses, your cervical mucus increases in volume and changes texture. You are most fertile when the mucus becomes clear, slippery, and stretchy.
  • Basal body temperature chart. Taking your temperature when you awake each morning, before you get out of bed and plotted in a chart (BBT Chart). After ovulation your basal body temperature increases about half a degree due to the effect of the hormone progesterone. Once your temperature rises, you have already ovulated. This means it is likely too late to conceive.