Ovulation Calculator

If you happen to have irregular periods, or just want to know more about how to calculate ovulation, there are several other ways to pinpoint when you’re most fertile.

How to Calculate Ovulation

Barring fertility procedures, sex is obviously essential when you’re trying to conceive. But there’s a bit of science and math involved too. Not up for crunching numbers by hand? An online ovulation calculator is a quick and easy way to figure out the days on which you’re most likely to conceive. Simply plug in the first day of your last menstruation and your average cycle length into The Bump ovulation calculator above. It’ll create an ovulation calendar marking your estimated ovulation date in green and other top fertility times in a lighter shade. Now it’s up to you and your partner to have sex on days designated by the fertility calculator. But that doesn’t mean you have to have sex every single day during your fertility window to conceive—since sperm can live in your body for up to three to five days, having sex every other day, or even every third say, is perfectly sufficient.

Of course, you can use other methods to calculate ovulation as well. Keep reading to learn how to put together an ovulation calendar.

Tracking Menstrual Cycles

You may have heard that ovulation happens on day 14 of your monthly cycle and that “normal” cycles are 28 days—but that’s actually not true for most women. (In fact, one study found that only 13 percent of women had 28-day menstrual cycles.) The average menstrual cycle for most women is between 21 and 35 days, and ovulation usually occurs 14 days (give or take a day) before you get your next period again. This means the exact day that ovulation takes place depends on your unique cycle length. Keep a menstrual calendar for at least three months to get a good sense of your cycle length, then mark the first day of your next period and count 14 days backward to calculate ovulation by hand.

Once the egg is released, it has 12 to 24 hours to be fertilized before it’s no longer viable—but you don’t have to have sex on the precise day of ovulation in order to get pregnant. In fact, you’re fertile for six days: the five days leading up to ovulation and the day you ovulate. Within that window, you’re most fertile during the two to three days before ovulation and the day of ovulation itself. That’s because while your egg only lasts for a day, sperm can live inside your body for three to five days—so it's possible to have sex before you ovulate and still conceive a few days later.

Ovulation Kits

An ovulation kit is another easy, accurate way to put together an ovulation calendar. An over-the-counter ovulation tracker tests your urine to detect specific hormones that your body produces in the lead up to ovulation. For example, while the luteinizing hormone (LH) is always present in your urine, the levels spike 24 to 48 hours before ovulation. (This LH surge is what actually triggers ovulation.)

The instructions in your ovulation kit will direct you when in your cycle to begin testing. Much like an at-home pregnancy test, you’ll pee on a stick and wait for the results. The ovulation tracker will then indicate whether you’ve reached a high fertility or peak fertility day. When used correctly, ovulation kits are said to be about 99 percent accurate in detecting the LH surge that happens before ovulation, and therefore can serve as a reliable ovulation calculator. When you get the positive sign that your LH surge is happening, the best times to have intercourse are that day and the following two days. Note, though, that the test can’t confirm whether ovulation actually occurs a day or two later. It is possible for women to have the LH surge and then not release an egg.

Signs of Ovulation

An ovulation calculator and ovulation calendar based solely on your menstrual cycle or an over-the-counter ovulation kit aren’t your only indicators of when you’re most fertile. Your body actually gives off ovulation symptoms, which serves the same purpose as an ovulation tracker. Here are a few signs to keep a lookout for:

• Clear, stretchy cervical mucus that resembles egg whites
• Heightened sense of smell
• Sore breasts
• Mild pelvic pain on one side
• Light spotting
• Spike in your libido

Keep in mind that these symptoms are different for each woman; some women may notice all of them and others may notice only a few or none of them.

Tracking Basal Body Temperature

Keeping track of your Basal body temperature—aka your morning body temp before you get out of bed—is yet another way you can pinpoint your ovulation calendar. After the egg is released, your Basal body temperature rises by about half a degree. (Because the change in body temperature is so slight, you’ll need to pick up a special thermometer.) Keep in mind, though, that the change in temperature happens 12 to 24 hours after ovulation, so it’s not a sign that the egg is about to be released, but a sign that ovulation already occurred. If your cycle is regular, tracking your Basal body temperature for a few months will clue you into when in your cycle you ovulate. In that way, it can be a useful ovulation calculator.

Whatever method you use to put together an ovulation calendar—an online ovulation calculator, an ovulation kit, your body’s signs of ovulation or detecting a rise in your Basal body temperature—The Bump is here to help you on your journey from conception to growing your family.

Medical content was reviewed August 2020 by Temeka Zore, MD, a board-certified ob-gyn and reproductive endocrinologist and infertility specialist at Spring Fertility in San Francisco.