Ovulation occurs when one of your ovaries releases a mature egg, which makes its way through the fallopian tubes, to be fertilized by sperm. Each woman’s cycle is different, and ovulation timing is complex, so tracking your ovulation cycle will require some degree of studying your body and its cycle. However, by employing a combination of methods—including tracking your periods, checking your basal body temperature and observing your cervical fluid—you can better determine when you’re ovulating. This group of methods, commonly referred to as fertility awareness or natural family planning, is about 90 percent effective in calculating your ovulation cycle if used correctly and consistently.
Method 1: Figuring out your cycle
Your monthly cycle begins on the first day of your menstrual period and ends on the first day of your next period. The average monthly cycle lasts between 28 and 32 days, though some women’s cycles may be shorter or longer.
Tracking your menstrual cycles each month can help you determine when you’ll be most fertile and narrow down when you’ll ovulate, which only lasts about 24 hours. The American Pregnancy Association recommends tracking your cycles for about eight to 12 months, as menstruation and ovulation can easily change each month.
Once you’ve compiled a solid diary of your cycles, choose the longest and shortest cycles from your records. You can calculate your fertility window—the time period in which you are most likely to get pregnant—using your diary and simple math.
To figure out the first day that you’ll be fertile, take the length of your shortest cycle and subtract 18 days. For example, if your shortest cycle was 28 days long, so you’ll subtract 18 from 28. The remainder—in this case, 10—indicates your first day of fertility will occur on the 10th day of your cycle.
To determine which will be your last fertile day, you’ll take the span of your longest cycle and subtract 11 days. For instance, if your longest cycle was 30 days, you’ll subtract 11 from 30, which leaves you with 19. Your last day of fertility will be the 19th day of your cycle.
Based on these examples, then, your fertility window will span between days 10 and 19 of your cycle, during which you will ovulate for 12 to 24 hours. The majority of women ovulate sometime between the 11th and 21st day of their cycle, starting from the first day of the last menstrual period. However, ovulation can happen on any day during your fertility period. Because menstruation and ovulation can easily change each month, it’s wise to track your ovulation using the other methods as well.
Method 2: Taking your basal body temperature
Another method that can help you determine when you’ll be most fertile and likely to ovulate is by tracking your basal body temperature, which increases between 0.4 and 1 degree Fahrenheit when you are ovulating.
Using a basal thermometer, take your temperature each morning before getting out of bed and record your temperature readings. You’ll see your temperature will remain normal and pretty consistent before you ovulate. When ovulation is about to occur, you may notice a slight decrease in your temperature. Once you have ovulated, however, your body temperature will rise and remain elevated until you start your next cycle.
Method 3: Examining your cervical mucus
You may have noticed that your cervical mucus increases and changes consistency throughout your cycle. Following a menstrual period, you will experience about three to four days in which you don’t have much vaginal mucus. Your mucus production will then begin to increase, which will last for about nine days until you experience the wettest day, where your mucous will have a consistency much like egg whites: slippery, clear and stretchy. You will ovulate within one to two days when the mucous is its slipperiest, clearest and most stretchy.
Using this methodical triad to figure out when you’re most fertile and ovulating can be highly effective—and cost-effective, costing little to nothing—if you diligently track and record your cycles, temperatures and vaginal mucus consistencies. However, if you find it unappealing to track these three ovulation predictors but still want to know when you’ll be ovulating, you may want to consider using an ovulation prediction kit, which can indicate your fertile days and alert you to an increase in the luteinizing hormone (LH), which happens about a day or two prior to ovulation.