Ovulation calculator: Figure out your most fertile days

If you’re trying to get pregnant, it pays to know what ovulation is and when it might happen for you. This is the big event each cycle when one of your ovaries releases an egg and is when you’re most fertile. We only have a small fertile window each month during which we can conceive, so if you’re trying, it’s handy to know when this is for you. 

By using some basic information about your cycle, such as the first day of your last period, Flo’s ovulation calculator can predict when you might ovulate, so you know your most fertile days. Here’s everything you need to know. 

Key takeaways on calculating your fertile window

• Knowing when you ovulate helps you identify your fertile window and, therefore, the best time to have sex to get pregnant. Ovulation calculators use one set of your cycle dates and can help you figure out your time of ovulation. 
• If you’d like even more accurate predictions for when you might be in your fertile window, you can download an app like Flo. 
• While the average menstrual cycle is considered to be 28 days, and ovulation generally happens midway through or around day 14, this isn’t the case for everyone. If yours is between 21 to 35 days, then it’s still considered to be typical. 
• There are signs of ovulation to know, such as changes to your cervical mucus and a slight increase in your basal body temperature (BBT, your natural temperature when you’re resting).
• Some people also say they feel cramps, breast tenderness, and increased sexual desire at this point in their cycle.

How are your fertile days calculated in the ovulation calculator? 

Once you’ve decided that you’d like to start a family, it’s natural to want to do all you can to maximize your chances of conceiving. One way you might do this is by ovulation tracking and using an ovulation calculator to establish when you’re most likely to conceive during your cycle. 

Firstly, ovulation is the point in your cycle when your body releases an egg to be potentially fertilized by a sperm. Once it’s been released, your egg will travel down one of your fallopian tubes, and for the next 12 to 24 hours, it’s what doctors call “viable” or able to be fertilized. If you have sex during this time, then you might become pregnant. 

A wild fertility fact is sperm can live in your body for up to five days after sex. That means your fertile window spans around six days in total: the five days before ovulation plus one day after. 

Having lots of sex around ovulation can indeed boost your chances of getting pregnant. And using an ovulation calculator can help you time this. 

Since your time of ovulation can change from cycle to cycle to cycle, Flo can’t give you an exact day of ovulation. However, using the first day of your last period and your average cycle length, Flo can help you predict the window of when you might ovulate. 

“The standard for ovulation time is midway through your cycle,” explains obstetrician and gynecologist Dr. Charlsie Celestine, New Jersey, US. “So a 28-day cycle generally ovulates on day 14. However, if your cycle is longer or shorter, then this midpoint date fluctuates along with that. For example, a 21-day cycle might ovulate on day 10 or 11.”

What’s the average length of a menstrual cycle? 

When it comes to our menstrual cycles, it can be tough to make generalized predictions. Everyone is slightly different. The average cycle length is considered to be about 28 days. However, research shows this textbook 28-day cycle isn’t the case for most people. 

Normal menstrual cycles can range from every 21 days to every 35 days. The time between ovulation and your next period will usually be about 14 to 16 days, though. Again, this can slightly differ. Sometimes, you might experience early ovulation, for example. Using a cycle-tracking app like Flo can help you understand what your normal is. 

What are the signs of ovulation? 

There are lots of ways to track ovulation. You can use an app like Flo, and your body also gives off subtle signs of ovulation. Some people prefer to monitor body signs as well as using ovulation tests. These can include: 

• A change to your cervical mucus: One sign that ovulation is happening soon is a change in your vaginal discharge (cervical mucus). This discharge may be different from what you might usually see in your underwear; it could be clear and have a thinner, more slippery consistency, similar to raw egg whites.
• Increase in basal body temperature: After ovulation, you might also experience a small rise in your BBT. This is the temperature of your body when you’re resting. It may rise by around 0.5ºF (0.3ºC). We aren’t expecting you to notice this without a little help. You may be able to notice the change on a digital BBT thermometer if you consistently track your temperature around the same time each day, preferably first thing in the morning. 
• Changes to your cervix: Examining your own cervix can be tricky, so before we dive into this, know that checking changes to your cervix isn’t recommended if you’re monitoring ovulation. Checking your BBT and tracking changes to your discharge can be much easier. However, if you’d like to get to know your body better, then it’s handy to know that your cervix changes in texture and position during your cycle. You might notice that during ovulation, it will be higher and feel soft. You’ll also notice that after ovulation is over, it becomes much harder again. 

You can think of the changes to your cervical mucus as a big sign that ovulation is about to happen, and changes to your BBT mean that you’ve just ovulated. However, some people report feeling different symptoms, which can mimic how you feel just before your period starts. They include: 

• Cramps 
• Breast tenderness 
• Changes to your sex drive 
• Bloating 

Can ovulation tracking increase your chances of pregnancy?

Ovulation tracking can increase your chances of pregnancy by helping you identify your fertile window — the days when you are most likely to conceive. Research suggests that couples who have sex one to two days before ovulation are most likely to conceive.

But ovulation tracking using dates or apps isn’t foolproof, explains Dr. Celestine, as your cycle length can change from month to month. 

“The best way to track it yourself would be an ovulation predictor kit where you urinate on a stick, similar to a pregnancy test,” she reveals. They measure levels of a hormone called luteinizing hormone (LH) in your urine, as this surges right before you ovulate. 

The surge in LH happens on average around 36 hours before ovulation, so start testing two or three days before the ovulation calculator says you’re likely to ovulate. It’s a good idea to track your ovulation over two or three months using ovulation tests, explains Dr. Celestine, to give you useful data to show a health care professional. 

“If there’s no ovulation at all in this time, or if you are getting positive ovulation results but have been trying to get pregnant for over a year (if you’re under 35) or six months (if you’re over 35), then see your doctor.” If you have an irregular cycle or have a condition like polycystic ovary syndrome (PCOS), the results from ovulation predictor kits may not be accurate or helpful, so reach out to your doctor.