Ovulation Calculator

Select the first day of your most recent period and the average number of days from the start of one period to the start of the next. The calculator projects your likely ovulation date and fertile window for six cycles, along with the due date a pregnancy conceived in each cycle would have.

Ovulation and Conception

Ovulation is the release of a mature egg from one of the ovaries, usually once per menstrual cycle. It is triggered by a sharp rise in luteinizing hormone (LH). After release, the egg travels into the fallopian tube, where it can be fertilized for only about 12 to 24 hours.

Sperm last much longer: in fertile cervical mucus they can survive in the reproductive tract for up to five days. That is why the fertile window spans about six days, the five days before ovulation plus the day of ovulation itself. Research led by the US National Institute of Environmental Health Sciences found that nearly all pregnancies came from intercourse in this six-day window, with the highest chances in the two or three days just before and on the day of ovulation. Having sex every one to two days during that time gives the best odds; there is no benefit in saving sperm by abstaining.

Ovulation Prediction

A menstrual cycle has two halves. The follicular phase runs from the first day of bleeding until ovulation, and its length varies a lot between people and even between cycles. The luteal phase runs from ovulation until the next period and is much steadier, typically about 14 days. Counting back 14 days from the expected start of the next period therefore gives a reasonable guess at ovulation. In a 28-day cycle that is day 14; in a 32-day cycle it is around day 18; and in a 24-day cycle around day 10.

Calendar estimates work best when cycles are regular. Stress, illness, travel, breastfeeding, recent hormonal contraception, thyroid problems and polycystic ovary syndrome (PCOS) can all delay or prevent ovulation. If your cycles vary by more than a week, a calendar alone will often miss the fertile window, and the methods below become more useful.

Ovulation predictor kits are urine tests that detect the LH surge. A positive result means ovulation is likely within about 24 to 36 hours, so the day of the positive test and the next two days are prime time. Cervical mucus changes too: as estrogen rises before ovulation it becomes clear, slippery and stretchy, like raw egg white. Basal body temperature, measured with a sensitive thermometer before getting out of bed, rises by about 0.5 to 1 °F (0.3 to 0.5 °C) after ovulation and stays up until the next period; it confirms ovulation after the fact, which helps you learn your pattern over several months. Some people also notice one-sided pelvic twinges, breast tenderness or a change in libido around ovulation.

Most couples conceive within a year of trying. ACOG recommends seeing a doctor after 12 months without pregnancy if you are under 35, after 6 months if you are 35 or older, and sooner if periods are very irregular or absent or there is a known fertility concern. Starting a daily supplement with 400 micrograms of folic acid at least a month before trying is advised for anyone who could become pregnant.

Ovulation ≈ next period start − 14 days; fertile window = ovulation − 5 days through ovulation day

The luteal phase, from ovulation to the next period, is fairly constant at about 12 to 14 days, so longer or shorter cycles move ovulation later or earlier.

Frequently asked questions

Sources

• ACOG – Fertility awareness and trying to conceive
• NICHD – Infertility and fertility
• Office on Women's Health – Your menstrual cycle