When Does Ovulation Occur? Calculate the Best Time to Conceive.
Medically reviewed by Nicole Galan, RN on August 16, 2019
Knowing when you ovulate is one of the most important ways you can increase your chances of getting pregnant. Your chances of conceiving are highest when you have sex in the days just before ovulation. But how do you know when ovulation will occur?
How many days after your period are you the most fertile?
Ovulation is what determines when you are most fertile—not when your last period ended. You can use online ovulation calculators to estimate when ovulation will occur, but these are not very accurate. The only data these calculators use is your average cycle length.
The most common pattern is for ovulation to occur 14 days before your next period is due. But if your cycles aren’t regular, this method won’t be very helpful, since you don’t know exactly when to expect your next period.
The reason why ovulation calculators make this assumption is because the average luteal phase (the time between ovulation and the next menstrual period) is 14 days long. But relying on this type of assumption could cause you to completely miss your fertile window. In fact, for up to 70 percent of women, the fertile window does not fall entirely within the days predicted by clinical guidelines. It’s much more accurate to track physiological signs and symptoms of ovulation.
What are the signs that you are ovulating?
Before ovulation, estrogen levels increase, and afterward, progesterone levels increase. You can look for signs of increased estrogen levels to know that your body is preparing to ovulate, and you can look for signs of increased progesterone to confirm that it occurred.
Estrogen-related signs (to predict ovulation):
- Cervical mucus
- Ovulation predictor kits (OPKs)
- Increased resting pulse rate
Progesterone-related signs (to confirm ovulation):
- Increased temperature
- Additional increase in resting pulse rate
Even when you track all of these signs, it can be difficult to know exactly what day ovulation occurred. The good news is, you don’t need to know exactly when you ovulated in order to get pregnant. The most important thing is to have sex on the days when you know you are fertile—when your body is exhibiting signs of preparing for ovulation. For your best chances, keep having sex at least every other day until you have confirmed that ovulation has occurred.
Vaginal Discharge (aka Cervical Mucus)
Cervical mucus nourishes and protects sperm inside the female reproductive tract, helping them along on their journey to the egg. Chances of conception are highest when fertile-quality cervical mucus is present.
Cervical mucus follows a predictable pattern throughout the menstrual cycle. After menstruation ends, cervical mucus is scant. As estrogen levels rise, cervical mucus increases and changes in consistency, from sticky, to creamy, and finally to the most fertile kind: raw egg white or watery.
These changes are driven by estrogen: when estrogen levels increase, it directly affects the quality of cervical mucus. Since estrogen must increase in order for ovulation to occur, observing the changes in your cervical mucus is an excellent and effective method for estimating when ovulation will occur. Typically, ovulation occurs on the last day of fertile cervical mucus (but of course, you never know when the last day of fertile mucus is until the next day).
Cervical mucus does not confirm that a mature egg was released, only that estrogen levels are increasing as your body gears up to ovulate. It’s important to combine cervical mucus observations with temperature in order to know when ovulation occurred.
Ovulation Predictor Kits
Ovulation predictor kits (OPKs) are urine tests that look for the presence of luteinizing hormone (LH) in your urine (some OPKs can also detect the presence of estrogen, as well as LH, but for this article, we will refer to the LH tests only). LH is the hormone that tells your ovaries to release an egg.
For most of your cycle, LH levels are low and variable. But when estrogen levels get high enough, it triggers a surge in LH. Most women ovulate about 24 hours after the beginning of the LH surge.
The length of the LH surge can vary from woman to woman, and so can the time lag from the beginning of the LH surge to ovulation.If you have a short LH surge, you may need to use OPKs multiple times per day to catch it. A positive OPK doesn’t tell you exactly how close to ovulation you are—it could be a few hours or a few days away. The probability of conception drops abruptly after the LH surge, meaning that if you wait for a positive OPK to have sex, you could be missing some of your most fertile days.
Resting Pulse Rate
According to a 2017 clinical study, resting pulse rate (RPR) begins to increase in the days before ovulation. RPR is lowest during your period, and increases by about two beats per minute up to five days before ovulation. After ovulation, RPR continued to rise, reaching a peak during the mid-luteal phase.
RPR is one of the seven parameters tracked by the Ava bracelet.
Basal Body Temperature
Basal body temperature (the lowest temperature your body reaches in a 24-hour period) increases by about .5 degrees Fahrenheit after ovulation, and remains elevated until the next period begins. If you take your temperature with a sensitive thermometer every morning at the same time, before getting out of bed or moving, you can see the increase in temperature that occurs after ovulation.
One of the biggest problems with using temperature to track ovulation is that by the time you see your temperature increase, it is already too late to conceive that cycle. Your fertile window is the five days before ovulation and the day of ovulation itself (the days with the highest chances of conception are the two days before ovulation). Since temperature does not rise until after ovulation,
Another problem with tracking BBT is that there is some variability in how long it takes for temperature to rise after ovulation. In a 2003 study that compared various cycle tracking methods with ultrasound-determined day of ovulation, it was found that temperature often does not increase until several days after the mature egg is released.
A biphasic temperature pattern is a strong sign that ovulation has occurred within the past several days, but it does not tell you the exact day that ovulation occurred.