Implantation calculator: When does implantation occur?

How to use the implantation calculator

Did you know that during every menstrual cycle, you have a fertile window — the six days when you’re most likely to get pregnant? During this time, your body releases an egg (this is called ovulation), and if it’s fertilized by a sperm, it may implant into the wall of your uterus and become an embryo. This is implantation in a nutshell and marks the 1st day of pregnancy. 

Knowing the date your last period started (when you had full flow), the date you may have ovulated, and the date that implantation may have happened gives you a better idea of when to take a pregnancy test. Trying for a baby really can feel like a numbers game. This is where Flo’s implantation calculator comes in. Keep reading to find out how it works plus everything else you need to know about implantation.

Remember that implantation predictors, calendars, and fertility calculators can help you learn more about your most fertile days and when you may have conceived. But they are for informational purposes only and cannot and should not be used to prevent pregnancy. Menstrual periods are different from person to person and month to month. Results are estimates, and actual implantation can vary for everyone.

How is your implantation date calculated?

If you know the day you ovulated 

After your ovaries release an egg during ovulation, there is only a 12- to 24-hour period where it will remain viable. It will start to make its way down your uterine tube, and if it is met and fertilized by a sperm in that period, then it may implant in your uterine wall. This process can take six to 10 days and is described as ‘days past ovulation’ or DPO.

You may already track your cycle using an app like Flo and know the day that you ovulated. If this is the case, then all you need to do is input the day that you ovulated and add six to 10 days to find out when your egg may have implanted.

Here’s what we mean: If you know you ovulated on day 18 of your cycle, then you’d figure out your implantation date by inputting 18 + (6 to 10 days) = potential implantation on day 24 to 28 of your cycle. If you’ve conceived naturally, without knowing when you ovulated, then it’s impossible to pinpoint the exact day that implantation may have occurred. However, this is slightly different if you’ve undergone in vitro fertilization (IVF). Keep reading to find out why. 

If you don’t know the day you ovulated 

If you aren’t sure what day you ovulated during your cycle, then you’ll need to figure that out before you can determine which day implantation may have happened. Don’t stress — you can do this by using an ovulation calculator or tracking your cycle using an app like Flo. 

Alternatively, you can estimate the day that you last ovulated by taking the date of your last period, adding how long your average cycle is, and subtracting 14. You might be curious where the number 14 comes from. The average menstrual cycle length is anywhere between 21 to 35 days long, and on average, the luteal phase is 14 days (hence subtracting 14 days). However, this can differ from person to person. Your cycle starts on the first day of your period and ends on the day before your next period. 

For example, if your last period was on the third of the month, and your average cycle length is 29 days, you would input 3 + 29 - 14 = ovulation around day 18 of the month. Once you have this information, you can figure out when implantation may have happened using the calculator above. 

Understanding implantation calculator results

Once you’ve inputted the day you ovulated, plus the six- to 10-day range that it takes for your fertilized egg to travel down your uterine tubes, you’ll be left with a time frame of around four days when implantation may have happened. So, what does this mean?

“There are lots of ways to track how far along a pregnancy is,” says Dr. Jennifer Boyle, obstetrician and gynecologist at Massachusetts General Hospital, Massachusetts, US. “This can be done by tracking menstrual cycles and trying to notice when ovulation takes place. Knowing when implantation may have occurred can help someone know when to take their first pregnancy test.”

What is implantation, and when does it happen?

Implantation is the term used to explain when a fertilized egg (sometimes called an embryo) attaches to your uterine lining. On average, implantation happens around six to 10 days after you’ve ovulated and the egg was fertilized. 

What happens with the pregnancy hormone human chorionic gonadotropin (hCG) during implantation?

You might be curious about the link between implantation and when you can take a pregnancy test. When a fertilized egg implants into the lining of your uterus, it triggers your placenta to start forming. The placenta is a new organ that develops during pregnancy to provide nutrients and oxygen to your baby. As it starts to grow, your placenta releases the pregnancy hormone human chorionic gonadotropin (hCG) into your bloodstream and urine. It can be detected in a blood test from around six to 10 days after you’ve conceived but takes longer to show in a urine test. It’s considered to be one of the earliest indications of pregnancy. 

HCG plays a crucial role in your 1st trimester of pregnancy. It triggers your body to produce more progesterone. These hormones signal for your body to stop releasing eggs (stopping ovulation) and support your pregnancy as it develops.

Your hCG levels rise rapidly in the first few weeks of pregnancy. In fact, during the first 8 to 10 weeks, your hCG levels can almost double every 48 hours. However, this can differ from person to person. HCG levels can really vary in early pregnancy, so if yours don’t double during this period, then don’t worry. Your doctor may examine your hCG levels during your initial prenatal appointment to establish how your pregnancy is progressing.

How soon can you test for pregnancy after implantation?

It’s hCG that many at-home pregnancy tests look for in your pee. If you’re thinking about taking a pregnancy test, then it’s key to know when your hCG levels might start showing up — and when they’ll be high enough to provide you with an accurate result. 

“At the time of a missed period, if a person is pregnant, their hCG level should be high enough to be detected using a standard home pregnancy test,” says Dr. Boyle. “It’s hard to wait, but it’s even more stressful and confusing to get a result you are not sure about.” 

Studies have highlighted that tests taken on the first day that you miss your period can be considered to have 90% sensitivity at detecting hCG. This rises to 97% if you wait one week after you’ve missed your period. So generally speaking, the best time to test for pregnancy after implantation is on the first day of your missed period or after that point. If you have a pregnancy test that comes back positive, then your doctor may also do a blood test to check your hCG levels. 

How can I know if implantation was successful?

Some people say they knew the day they got pregnant based on symptoms or signs they noticed around the days that implantation may have happened. While it can be fun to guess when you conceived, the only way to know if implantation was successful is by taking a pregnancy test. The best time to do this is after you’ve missed a period. Implantation symptoms aren’t medically recognized, but some people report feeling:

• Implantation bleeding: This is light spotting or bleeding around two weeks after conception. This may come around the time of your period but will be lighter. You might mistake implantation bleeding for your period. 
• Bloating: As your hormone levels rise at the start of pregnancy, you may experience some bloating. 
• Cramping: Some people report feeling minor cramps during implantation. 
• Fatigue: Following implantation, you may feel more tired than usual. Tiredness is a key symptom that many people experience throughout the 1st trimester. 

You won’t likely hear your doctor talk about implantation symptoms. Instead, they may talk about any symptoms you have as early signs of pregnancy. You may also notice some similarities between early pregnancy symptoms and symptoms of premenstrual syndrome (PMS). Period bleeding lasts longer than spotting around implantation — around two to seven days. If you’re unsure if the symptoms you’re experiencing are PMS or pregnancy, then reach out to your doctor. 

Is implantation different during in vitro fertilization? 

There is a key difference in predicting when implantation may have happened if you’ve undergone IVF. While it’s impossible to pinpoint the exact time that implantation happened if you conceived naturally, with IVF, you may have a better idea. “If a person undergoes IVF, they will know when the fertilized egg, or embryo, is transferred into the uterus,” says Dr. Boyle. “They will still not know, however, if the embryo has successfully implanted until their hCG test is positive.” 

IVF is made up of a series of procedures. After taking hormones to prepare your body, your doctor will retrieve mature eggs from your ovaries and will fertilize them with sperm in a lab. Once any viable embryos are ready, they will then transfer one or more (depending on what’s agreed beforehand) back into your uterus during a procedure called embryo transfer. An embryo implants within a few days after the transfer. If implantation is successful, then pregnancy may be detected in the days that follow.