How to Calculate Your Ovulation Period Using Your Menstrual Cycle
Ovulation is the phase in a woman's menstrual cycle when an unfertilized egg is released from the ovary and travels through the fallopian tubes and into the uterus. This is the stage of the menstrual cycle during which pregnancy can occur, if the released egg is fertilized by sperm.
I will explain how to use the length of your menstrual cycle to determine when you may be ovulating. I will also go through other ways of predicting and detecting ovulation, such as tracking your basal body temperature, cervical mucus, or purchasing an ovulation kit.
How Many Days After Your Period Do You Ovulate?
According to Ob/Gyn Dr. Tami Prince, MD, "Ovulation, which is the release of an egg from the ovary, usually occurs approximately 14 days prior to the next period." Count the number of days from the first day of your period to the day before you next period to determine the length of your cycle. Then subtract that number by 14 to determine what day after your period you will ovulate. If your average menstrual cycle is 30 days, you will ovulate 16 days after your period starts (30-14=16).
Predicting ovulation is not foolproof, meaning there can be a margin of error in pinpointing the exact time of ovulation. Prediction can be off by at least 2 days.
How to Figure Out When You're Ovulating
1. Calculate the Length of Your Menstrual Cycle
- Make a note of when your next period starts. This is the first day of your cycle.
- Then, make note of when your period comes again in the following month. This is the beginning of the next cycle.
- When you count the days in between, this gives you the length of your cycle.
Here's an example:
- Period starts: January 1
- Next period starts: January 31
- Days in between (including January 1 but not January 31): 30 days. The menstrual cycle length, therefore, is 30.
You might want to do this for more than one month, as menstrual cycles can vary in length from month to month. This will also help you determine if you have an irregular cycle, in which you may skip periods for a month or more at a time. An irregular cycle will make predicting ovulation more difficult.
2. Calculate When Ovulation Starts
If you have a 30-day cycle, then ovulation will occur approximately on day 16 of your cycle. Ovulation occurs 10-14 days before your next period, so you will get an approximate ovulation date by subtracting 14 from the number of days in your cycle (eg. 30 days minus 14 = 16). This means that ovulation will occur 16 days after your period starts. If you have your period on January 1, ovulation will take place on January 17.
Use the chart below to determine when you're most likely to ovulate based on the length of your menstrual cycle. Find the length of your cycle in the left-hand column to see how many days after the beginning of your period you will ovulate and when you're at your most fertile.
When Does Ovulation Start?
Cycle Length (Days)
Most Fertile Days
How Do I Calculate My Fertile Window?
In a regular cycle, a woman's fertile window is the day of ovulation (usually 10 to 14 days before her period begins) and the five days before it. For an average 28-31 day cycle, the fertile window would be somewhere between days 14 and 17. Many doctors recommend having sex a few days before ovulation because sperm can live up to five days in a woman's reproductive tract and will already be present in the woman's body and be ready to meet the egg when it eventually releases.
What Are the Most Fertile Days After Your Period?
You are most fertile the day before ovulation and the day of ovulation. According to Dr. Hanh Cotrell from IVF Michigan, "Your fertile window is about a week prior to anticipated ovulation." So if you are trying to conceive, she recommends having sex every day to every other day during that week to give you the highest chance of pregnancy. You are not likely to get pregnant right after your period, although it can happen if you have an abnormally short menstrual cycle, in which ovulation could happen just a few days after your period ends.
Here's an example of your most fertile days for a 30-day cycle:
- First day of period is January 1
- Next period will begin on January 31 (30 days after January 1)
- Ovulation will take place anywhere from January 17 to January 21 (10-14 days before your next period). These are your most fertile days.
- You can have sex up to 5 days before this period and still get pregnant.
Can You Get Pregnant During the Luteal Phase?
It is very unlikely. The luteal phase occurs after ovulation when a woman's body stops releasing eggs, so it is impossible for sperm to find an egg to fertilize during this phase. However, an unfertilized egg survives up to 24 hours before dissolving, so if you have sex 12-24 hours after ovulation, there is still a small chance that you could get pregnant.
How Long Does the Luteal Phase Need to Be to Get Pregnant?
Your luteal phase length should be 12 to 16 days. It begins after ovulation and ends with the onset of your next period. During this time, progesterone rises and signals the growth and thickening of your uterine lining where the fertilized egg will implant itself and develop into a baby. If your luteal phase is shorter than 10 days, the fertilized egg will not be able to attach, and you will experience an early miscarriage.
For Women With Irregular Cycles
Keep in mind that women with irregular cycles may not be able to predict when ovulation happens because the length of their cycle varies month to month. It is possible for some women with irregular cycles to ovulate right after their period, though this is uncommon.
Other Ways to Detect or Predict Ovulation
Basal Body Temperature
Your basal body temperature (BBT) is your lowest temperature in a given 24-hour period, most likely early in the morning when you first wake up. Two or three days after you ovulate, your BBT should rise about 0.4 to 1.0 degrees Fahrenheit due to hormonal changes and stay that high during your period. To track your BBT, follow this step-by-step guide on how to chart your basal body temperature. Only tracking your BBT for one month will not help you predict ovulation as the temperature rise occurs after the fertile window. But by tracking your BBT over several months you can see patterns in your hormonal fluctuations, and then predict when you may be ovulating.
An ovulation kit can be easily purchased and used to test your urine for elevated levels of luteinizing hormone just before ovulation. Ovulation kits can accurately predict ovulation 12 to 36 hours ahead of time, and unlike other methods, can predict ovulation during the first month of using them.
Monitoring Cervical Mucus
The consistency and color of vaginal discharge will change over the course of a month, due to hormonal fluctuations. Examining your cervical mucus can give you some indication of where you are in your cycle. Right before ovulation, your vaginal discharge will become clear and develop the consistency of a raw egg white. The last day you see mucus of this consistency is the day before or day of ovulation, when you're most fertile.
Cervical Mucus Stages
- After Period (1-3 days): Dry
- After Period (days 4-6): Sticky. You might find white globs.
- Before Ovulation (days 7-9): Thick, white or cloudy discharge. Abundant.
- During Ovulation (days 10-14): Clear, stretchy, and slippery, like raw egg white.
- After Ovulation: Thick and creamy white or yellow.
Remember, you are most fertile during ovulation, so if you see clear slippery mucus similar to egg white, you are ovulating!
Signs and Symptoms of Ovulation
According to Dr. Kelly Kasper, an OBGYN from Indiana University Health, the extent of the following ovulation symptoms vary from woman to woman, but the majority of women will experience at least one of these symptoms as they approach their ovulation period.
- As a woman nears ovulation, her body produces more estrogen causing the cervical mucus to become thick, clear, and stretchy, which helps the sperm swim to the egg that is released during ovulation.
- Some women will experience breast tenderness or sensitivity due to the change in hormones before and after ovulation.
- A woman may experience a heightened sense of smell in the second half of the cycle after ovulating in order to be more attracted to androsterone, a male pheromone.
- A woman may experience light spotting or brown discharge, which is normal. When ovulation occurs, the follicle that surrounds and protects the egg can rupture and result in a small amount of bleeding. This blood turns brown as it gets older, hence why the vaginal discharge can be red to dark brown.
- A woman may notice that her sex drive (libido) increases during ovulation.
- Some women will complain of a mild ache or pain on one side of the pelvis during ovulation. This pain is known as Mittelschmerz, or "pain in the middle." When a follicle matures prior to releasing an egg, the follicle can contain a small amount of fluid like a cyst. When the egg is released, the follicle ruptures releasing the fluid causing an ache or pain. This discomfort can last for minutes or hours and often alternates sides each month. Over-the-counter anti-inflammatory medications can be used to help alleviate the pain. If the pain is persistent or severe, a woman should see a doctor.
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.