Predict your ovulation window, fertile days and due date based on your menstrual cycle.
Ovulation in humans is the process by which ovarian follicles rupture and release one or more mature eggs from the ovaries. On average, ovulation occurs within the 4 days before or after the midpoint of a woman's menstrual cycle (14 days before the start of a woman's next menstrual period).
Day 10-18 of the menstrual cycle (on average) is the most fertile phase of the menstrual cycle. This is important when trying to conceive because fertilization of the egg can only occur for 12-24 hours after release during part of the luteal phase, when a mature egg travels through the fallopian tubes towards the uterus.
Since sperm can survive inside a woman's body for up to five days, regular sex five days before and on the day of ovulation can improve the likelihood of conception. If fertilized, the egg will implant in the uterus 6-12 days later. Otherwise, menstruation occurs, and blood and mucosal tissue from the inner lining of the uterus is expelled.
This calculator uses standard menstrual cycle physiology to estimate fertile windows:
The calculations are based on the standard 14-day luteal phase, which is relatively consistent between women. The follicular phase (before ovulation) varies more and accounts for most differences in total cycle length.
This ovulation calculator uses the method of tracking menstrual cycles in order to predict when ovulation occurs. Since day 10-18 of the menstrual cycle is typically the most fertile phase, women with regular cycles can fairly easily determine when they are ovulating and most likely to conceive.
The first day of the menstrual cycle is the day that bleeding starts, and it ends the day that bleeding starts again. It can be helpful to maintain a menstrual calendar to determine how regular your periods are. If they are irregular, other methods may be more accurate for estimating when ovulation will occur.
Basal body temperature (BBT) is measured using a special thermometer. This is your temperature when you first wake up in the morning. BBT is generally at the lowest level right before ovulation occurs. It starts rising by about ½ a degree a day during ovulation.
Tracking BBT over a few months can help you determine when you are ovulating. However, there are other factors involved that can affect your BBT, such as having a cold or infection, making it less reliable in some cases.
Over-the-counter ovulation tests detect a surge in luteinizing hormone (LH) that precedes ovulation by 24-48 hours. While these tests are 99% accurate in detecting the specific hormones, they cannot guarantee when exactly ovulation will occur within the two-day period.
There are also ovulation predictor kits that test changes in estrogen levels in saliva or salts in sweat. These changes generally occur earlier than LH increases, and can therefore predict ovulation earlier, but require more baseline tracking.
| Date | Timing | Significance |
|---|---|---|
| Intercourse Window | 5 days before ovulation through ovulation day | Days when intercourse is most likely to result in pregnancy (accounts for 3-5 day sperm survival) |
| Ovulation Window | 2 days before through 2 days after ovulation | Peak fertility period when fertilization is most probable |
| Ovulation Day | ~14 days before next period | Day the mature egg is released from the ovary |
| Pregnancy Test Date | ~9 days after ovulation | Earliest date a sensitive pregnancy test may detect hCG hormone |
| Implantation | 6-12 days after ovulation | Fertilized egg attaches to uterine wall |
| Due Date | 280 days from LMP | Estimated delivery date if conception occurs this cycle |
All dates provided by this calculator are estimates based on average cycle physiology. Actual ovulation timing can vary significantly between cycles and between individuals due to stress, illness, travel, hormonal fluctuations and other factors. This calculator is for informational and planning purposes only and does not constitute medical advice. It should not be used as a form of birth control or to guarantee conception. Always consult with a qualified healthcare provider for fertility concerns, family planning and reproductive health guidance.
1. American College of Obstetricians and Gynecologists. "Understanding the menstrual cycle."
2. Wilcox AJ, et al. "Timing of sexual intercourse relative to ovulation: effects on the probability of conception, survival of the pregnancy, and sex of the baby." NEJM 1995.
3. National Institute of Child Health and Human Development. "Ovulation prediction methods."