How far in advance can I tell when I'm ovulating?

The biology of making a baby sounds simple. Combine sperm and egg, and in nine months, you have an infant, right? Unfortunately, some of us need a little more planning. Body temperatures, calendars, rhythms … getting pregnant can certainly seem more like an art than a science. Just how well can you determine the most optimal time to conceive?
Conception can happen after a woman ovulates. Ovulation occurs every month about midway through a woman's menstrual cycle. During ovulation, a woman's ovary releases a mature egg, which then travels through the fallopian tube, where a sperm can fertilize it. If an egg isn't fertilized, it passes out of the body, and the cycle begins again.
After ovulation, you have a 12- to 24-hour window for the sperm to fertilize the egg, and when you're trying to conceive, that's not much time to get it right. On top of that, ovulation doesn't always occur at the same time during each monthly cycle. Factors such as significant weight changes, excessive exercise, stress and illness can all prevent you from ovulating regularly.
However, pinpointing the moment you ovulate doesn't have to be a roll of the dice. Your body does send signals to help you figure it out. Pay attention to these signs, and you may know when you're ovulating.

• Cervical mucus: Your cervical mucus changes throughout your menstrual cycle. Just before you ovulate, the amount of mucus increases and becomes sticky and slippery.
• Basal body temperature: Basal body temperature is your resting temperature. When you're ovulating, your temperature may rise slightly.
• Cramping: Some women experience slight abdominal cramping when they ovulate.

Now that you know what to look for when you ovulate, let's see if you can predict your actual day of ovulation.

Predicting Ovulation

Predicting when you're going to ovulate may take many months of data gathering, and even then, you might not get an exact day of ovulation. Still, knowing the days you'll be most fertile can help you conceive. Several tracking methods can help you notice the patterns in your menstrual cycle:

Basal body temperature -- Use a basal body thermometer to track your temperature to hundredths of degrees. You'll have to take your temperature right when you wake up because if you get out of bed, you could affect the reading. Chart your results for several months. If you see a rise in temperature, that denotes when you're ovulating. This method doesn't pinpoint the exact date of ovulation, but many women ovulate within three days of this temperature shift.

Calendar -- Take note when your period starts and mark it on a calendar. This is day one of your menstrual cycle. Also, keep track of how many days it lasts. Ovulation tends to occur two weeks before you begin your period, so if you track several months' worth, you'll be able to learn how long your average cycle is, which will help you estimate ovulation. For a 28-day cycle, this will be around day 14. If you have a longer or shorter cycle, you'll likely ovulate on a different day, possibly even while you're menstruating.

Cervical mucus -- The mucus your cervix produces changes throughout your menstrual cycle. During ovulation, it becomes thin, slippery, more translucent and stretchy.

Ovulation tests -- Over-the-counter ovulation predictor kits help pinpoint your most fertile days. They test either urine or saliva for the presence of luteinizing hormone (LH). LH increases dramatically for about two days before ovulation. When you see a surge of LH, an egg will be released within 35 to 44 hours. These tests can be pricy, and like the other methods, they only tell you when you're likely to ovulate. However, you don't have to track data for months.