Can you get pregnant after ovulation?

How ovulation works

Occurring at the end of the follicular phase (the first phase in the menstrual cycle), ovulation is the release of a mature, dominant egg cell. Once released, the egg lives for 12 to 24 hours in the female reproductive system, during which it is receptive to fertilization by a sperm cell. If it is fertilized, this is the beginning of pregnancy. If it is not fertilized, pregnancy does not occur, and your period begins, marking the start of a new cycle [1]. 

The fertile window and how to calculate it

The fertile window is the time in each cycle when there is a high likelihood that unprotected sex can lead to pregnancy. It lasts for six days and is determined by the timing of ovulation. Sperm cells can survive in the female reproductive system for up to five days and still fertilize an egg [2]. So the fertile window includes the five days before ovulation, plus the 24 hours during which the egg cell can survive for [3].  

Since the fertile window relies on the timing of ovulation, you need to know when you are going to ovulate to calculate your fertile window. If you regularly track your ovulation and menstrual cycle, you can get a good idea of when your fertile window is likely to occur in future cycles. Use our period calculator below to get an estimation of when your ovulation and fertile window might occur. Period calculators are a great initial guideline, but do not give the most accurate results and should not be used as birth control.

What affects ovulation?

Many tracking methods assume ovulation happens around day 14 of the menstrual cycle. But a Natural Cycles study of over 600,000 cycles found that the average day of ovulation was day 18, highlighting that ovulation timing can vary widely between individuals [4]. There are also external factors that can impact ovulation, for example: 

• Age: If you are over the age of 45, ovulation may be affected by the onset of perimenopause, when hormone levels fluctuate erratically, and your menstrual cycles (and ovulation) can become more irregular [5].

• Reproductive conditions: Some medical conditions can impact ovulation. For example, those with polyendocrine metabolic ovarian syndrome (PMOS, formerly PCOS) can often experience irregular and anovulatory cycles [6]. 

• Stress: Experiencing excessive stress can affect how your body produces and regulates hormones, potentially delaying or preventing ovulation [7].

Ovulation and irregular periods

Irregular periods are menstrual cycles that deviate from the norm of a typical cycle. Symptoms include: 

• Unexplained bleeding or spotting between periods

• Bleeding or spotting after sex

• Very heavy period bleeding, that soaks through one or more tampons or pads every hour

• Bleeding that lasts more than 7 days

• A menstrual cycle that is more than 35 days or less than 21 days

• Cycle length that varies by more than 7 to 9 days

• Not having a period for 3 to 6 months

• Bleeding after menopause

[8]

Many of us experience occasional irregular periods, which are usually nothing to worry about. However, cycle irregularities can sometimes be a sign of an underlying condition and, in some cases, indicate a problem with ovulation. When ovulation doesn’t occur (or is delayed), we don't experience the usual hormonal fluctuations that follow the release of an egg, and our periods can become unpredictable. A cycle in which we do not ovulate is called an anovulatory cycle [9]. 

Experiencing regular anovulatory cycles can cause difficulties if a person is trying to conceive. If you have any concerns about your menstrual cycle, often experience signs of irregular periods, or are having difficulties getting pregnant, speak to your doctor. 

Can you get pregnant after ovulation?

As we explained earlier, once ovulation occurs, the egg cell can survive for up to 24 hours. This is known as the ovulation window, during which pregnancy can occur. So, yes, you can get pregnant for up to one day after ovulation. Once the 12 to 24-hour ovulation window has passed, the egg cell is no longer viable and cannot be fertilized, so pregnancy is unlikely to occur [1]. 

What is the likelihood of becoming pregnant each day before or after ovulation?

Unprotected sex can lead to pregnancy at any time during the fertile window. But your chances vary each day within said window. An older study from 2000 looked at the menstrual cycles of 881 European women to predict when sex is most likely to lead to pregnancy. Using basal body temperature (BBT) as a guide for ovulation, the study found that within the fertile window, the best chance of conception is most likely two days before ovulation, and the lowest chance is five days before ovulation, at the window’s start. The table below shows the probability of getting pregnant for each day before and after ovulation [109]: 

While statistics like this can be useful for understanding fertility, it is worth remembering that many factors can impact your ability to get pregnant, including age, medical conditions, frequency of sex, fertility of both partners, and lifestyle influences. 

What methods are available to track or predict ovulation?

There are several ways you can track your cycle and predict when ovulation and the fertile window will occur. Each tracking method has its drawbacks, so it is better to use a mix of a few for a more accurate experience. We’ll first introduce a few fertility awareness methods before discussing ovulation tests and how Natural Cycles helps predict ovulation. 

Calendar method

The calendar method relies on counting cycle days and tracking your period to predict your fertile window. This is a common method used by cycle trackers, and there are a few different ways to use it. However, all versions of the calendar method rely on simplified assumptions about the menstrual cycle, such as cycle length and ovulation timing [11]. For example, the average menstrual cycle length is often quoted as being 28 days. However, our analysis of over 600,000 cycles found that the average cycle length was 29 days, ranging from 21 to 35 days [4, 12]. 

This leaves a lot of room for error using a calendar method that assumes a 28-day cycle. A second Natural Cycles study of more than 543,000 cycles found that calendar-based tracking frequently miscalculated “safe” days to have sex when avoiding pregnancy, and the risk of unintended pregnancy in users was higher than when using a regulated, digital contraceptive [13, 14]. 

Basal body temperature charting

Your basal body temperature (BBT) is your body’s lowest resting temperature, taken during sleep or immediately after waking [10]. BBT is closely linked with the menstrual cycle, and right after ovulation, your temperature will increase by approximately 0.5-1°F [15]. It then stays high until your cycle ends and your period begins. 

Since BBT rises after ovulation — and your fertile window is the five days before ovulation and the day of — the BBT method can’t predict your fertile window in advance. But once you have tracked your temperature for a while, you can begin to get an idea of where you are in your menstrual cycle and predict when your fertile window is likely to occur. If you are trying to prevent pregnancy, you can use BBT to indicate when it is best to have sex and when to avoid it or use additional protection. For those trying to conceive, it can help to know when the likelihood of conceiving is greatest.   

To use the BBT method effectively, there are a few things to keep in mind. You should use a special BBT thermometer with two decimal places to capture the subtle but significant change in temperature. There are different versions of the BBT method with varying guidelines, but you generally need to have three consistently high temperatures before you can assume ovulation has occurred [16]. If you want to use the BBT method to prevent pregnancy, you will need to abstain from sex (or use another method of contraception, such as condoms) until you have ovulated and confirmed with three consecutive high temperature days [16].

Cervical mucus tracking

Have you ever noticed your discharge change as you move through your cycle? Cervical mucus is a natural fluid secreted by the cervix. At the start of your cycle, it is usually drier. In the later follicular phase, it can look creamy before turning wet and clear as ovulation approaches. Around the time of ovulation, our bodies produce more “fertile quality” mucus to help protect and nourish sperm as it moves through the reproductive system. This mucus is stretchy and resembles egg white [11]. 

Since cervical mucus changes are linked to hormonal shifts and ovulation, you can use them as a marker of when you are most fertile by tracking them. However, this method comes with its limitations. To use it effectively, you need to be dedicated to accurate measuring and recording. Determining the quality and characteristics of cervical mucus can also be impacted by vaginismus, the presence of an STI, sexual arousal fluid, or residual semen [11].

The symptothermal method

Some individuals may choose to incorporate cervical mucus tracking in the “symptothermal method”. This is less a method in itself and more a way to combine multiple fertility awareness methods. The most common combination is using both the BBT method and the cervical mucus method. Fertility tracking can sometimes be more accurate with a combined symptothermal method than with a single method [11].  

If you are using any fertility awareness method (sometimes referred to as natural family planning) to prevent pregnancy, we recommend speaking with a healthcare professional or trained specialist to ensure correct use [17].

Ovulation predictor tests

A day or two before you ovulate, your level of luteinizing hormone (LH) rises, helping to trigger the ovulation process [187]. You can use at-home ovulation predictor tests to test for this hormone and know whether ovulation may be about to occur. These tests can be an excellent tool for predicting ovulation. But a positive test only indicates a surge in LH and suggests that ovulation is likely on the way, not a confirmation that it will definitely occur. The test also only indicates what is happening in our body at the exact time it is taken, so you may need to take a few tests at different times. 

Natural Cycles 

Unlike other fertility awareness methods or cycle trackers, Natural Cycles is FDA-cleared for use as hormone-free birth control. It uses a one-of-a-kind algorithm and biomarkers, such as BBT or body temperature, to analyze your unique cycle characteristics and predict ovulation, the fertile window, and your period. Compared to the calendar method or BBT charting, there is less need for doing calculations yourself. Instead, the app does the hard work for you and shows you your fertility status each day. You just need to enter your BBT data when you wake up in the morning, or use a compatible integrated wearable device that measures skin temperature trends while you sleep, such as the NC° Band. 

When to speak with a doctor about fertility

Always speak to your doctor if you have concerns about your fertility, especially if: 

• You have been trying to get pregnant for over a year (or six months if you are over the age of 35)

• You have a known condition that affects fertility, such as PMOS (formerly PCOS)

• You are experiencing symptoms of irregular periods (listed above)

• You are experiencing pain during sex

• You have a sexually transmitted infection (STI)

• You would like assistance using a fertility awareness method

More than a cycle tracker 

Natural Cycles makes tracking your fertility easy by combining temperature tracking with a one-of-a-kind algorithm to predict your fertile window. Whether you are looking to prevent pregnancy or plan pregnancy, you just need to check in with the app each day and log your biomarkers as needed to get your up-to-date fertility status. You can also enter ovulation test results and log symptoms, including cervical mucus characteristics, to better understand your body. There are different Natural Cycles experiences to match your fertility goals. NC° Prevent Pregnancy can be used as certified hormone-free birth control, whereas NC° Plan Pregnancy helps you confirm ovulation and get pregnant faster.