How to Calculate Your Ovulation
How Do I Know When I'm Ovulating?
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.
This Hub will explain how to use the length of your menstrual cycle to determine when you may be ovulating. It also explains other ways of predicting and detecting ovulation such as tracking your basal body temperature, cervical mucus, or purchasing an ovulation kit.
Step 1: Calculate the Length of Your Menstrual Cycle
You should make a note of when your next period starts. This is the first day of your cycle. Then, make note 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. 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.
Here's an example:
- Period starts: 1 January
- Next period starts: 3 February
- Days in between (including 1 January but not 3 February): 33 days.
The menstrual cycle length, therefore, is 33.
Step 2: Figure Out When You're Ovulating
Use the chart below to determine when you're most likely to be ovulating, based on the length of your menstrual cycle. Find the length of your cycle in the left-hand column, and determine how many days after the beginning of your period you are ovulating, and when you're at your most fertile.
Cycle Length (Days)
Most Fertile Days
Step 3: Determine Your Most Fertile Days
Use the same chart above to calculate the days of your cycle when you're most likely to conceive.
In the example below:
- Cycle length: 33
- First day of most recent period: 3 February
- Ovulation is 19 days after 3 February: 22 February
- Most fertile days are between 18 and 20 days after 3 February: 21-23 February
As a general rule, you are most fertile the day before, during, and the day after ovulation. That said, because sperm can survive for up to seven days in the right conditions, you could be fertile before and after these days. Also, research indicates that it is possible for some women with irregular cycles to ovulate during 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. 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.
- Monitoring Cervical Mucus: The consistency and color of vaginal discharge will change over the course of a month, due to hormonal fluctuations. Since one component of this discharge is cervical mucus, it can give 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.
- Ovulation Kit: 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.