Fertility tips

Implantation Calculator: When Did It Happen?

If you think you may have conceived this cycle, you might be looking for an implantation calculator. These little tools were developed to estimate when the fertilized egg may have burrowed into your uterine lining, thereby beginning your pregnancy. You’ll find a plethora of these nifty little calculators online promising to tell you your implantation date. But the reality is, they can’t.

Before getting into the details on why these calculators aren’t very accurate, here’s how they work. Implantation most often occurs 9 days after ovulation. Based on this information, there are two common ways to estimate when implantation occurs for you.

  1. If you know the date you ovulated, add 9 days.
Ovulation date + 9 days =  Implantation date
  1. If you know the first day of your last menstrual period (LMP), add 23* days.
Date of last menstrual period + 23 days =  Implantation date

*23 days =  14 (average number of days between LMP and ovulation ) + 9 (average number of days between ovulation and implantation)

Important note: The above calculations are a very oversimplified guess. The reality is that your cycle is variable and the day you ovulate won’t necessarily be consistent from cycle to cycle. So while using averages like 14 days (between LMP and ovulation) and 9 days (between ovulation and implantation) will tell you when implantation tends to happen on average for women as a whole, it won’t tell you much about when implantation happened for you.

What is implantation?

Implantation happens when a blastocyst (which started as a fertilized egg and is now growing while moving into the fallopian tubes) attaches to the uterine wall. This is the essential step for a viable pregnancy: once successfully attached, the blastocyst will continue to grow and become an embryo.

What does implantation mean for pregnancy?

When you’re trying to get pregnant, “When did I conceive?” is a pretty common question. However, a better question might be, “When did implantation occur?” Though many people think of conception—the moment a sperm fertilizes an egg—as the beginning of pregnancy, it’s probably more accurate to use the implantation date rather than the conception date. Implantation, or the process of the combined egg and sperm cells attaching to the wall of the uterus, marks the actual start of a viable pregnancy.

According to recent research published in Nature Biotechnology, conception occurs much more readily than implantation, but this does not ensure pregnancy. For the pregnancy to be viable, the cells must make contact with the endometrium and attach to the uterine wall. And only the fittest embryos—about one-third—manage to do that.

If progesterone hasn’t adequately prepared the endometrial lining to support life, or if the blastocyst contains abnormalities, implantation will fail. When this happens, the egg dies and is excreted during your next period.

When does implantation occur?

In most successful pregnancies, implantation occurs 8 – 10 days after ovulation. According to a recent study published in the New England Journal of Medicine, the estimated risk of early loss is strongly related to the time of implantation. The study found that early loss was least likely when implantation occurred by the 9th day past ovulation (DPO) and the risk increased with each successive day—most substantially after day 11*.

Here are the specific results:

Implantation Date (in Days Past Ovulation) Risk of early pregnancy loss
9 DPO 13%
10 DPO 26%
11 DPO 53%
after 11 DPO 82%

If implantation occurs later, it is more likely to result in early loss or a chemical pregnancy (chemical pregnancy is the term given to a miscarriage that occurs before the fifth week of gestation, and early loss is a miscarriage that happens in the first six weeks of gestation.). While it’s not fully understood why later implantation tends to result in early pregnancy loss, researchers speculate that embryos that are slow to implant must be impaired in some way. 

When did implantation occur for me?

Based on your knowledge of your last menstrual period or ovulation date, you can estimate when implantation might have taken place. (This is why tracking your cycle is incredibly valuable, as it can help you find out when ovulation occurs for your body, specifically.) If you have a pretty good idea of when ovulation happened, then you can estimate that implantation most likely happened  8 – 10 days past ovulation (DPO). 

How long does implantation last?

Most of the time, implantation follows a relatively stable timeline. Sperm can live for about five days, waiting for an egg’s release. Once an egg is released from the ovary, it begins a journey down the fallopian tubes and must be fertilized within 24 hours.

If a sperm does fertilize the egg, and the resulting blastocyst makes it to the uterus, it can still take several days to implant itself in the uterine wall. In all, the entire process usually takes 8 – 10 days, though, in some rare cases, implantation may occur as early as the sixth day, or as late as 12 days, after ovulation.  

What are the signs and symptoms of implantation?

Many women wonder when they can start expecting signs and symptoms confirming their hoped-for pregnancy. Who hasn’t Googled “early pregnancy symptoms” 24 hours after sex?

However, implantation symptoms are a debunked myth. Even though many sources use the word “burrowing,” which certainly sounds like it should feel like something, implantation involves only a few cells and causes no unique pain or cramping. In fact, the cramping people often associate with implantation cramps results from the high levels of progesterone already present during your luteal phase.

How about implantation bleeding? People talk about that all the time, right? Sorry, this one’s a myth, too. One study found that while 9% of women did experience light bleeding or spotting during early pregnancy, it was rarely on the day of implantation. Essentially, in the very early days of pregnancy, it’s nearly impossible to differentiate between the signs of an impending period and the signs of early pregnancy.

How long after implantation can I get a positive pregnancy test?

When you’ve got your fingers (and toes) crossed hoping for a positive result, there’s probably one insistent question looping through your mind: How soon can you take a pregnancy test?

Home pregnancy tests are most accurate when taken on or after the first day of your missed period, which usually occurs 12 – 14 days after ovulation. Pregnancy tests detect the presence of a hormone called human chorionic gonadotropin, or hCG, which is unique to pregnancy. Your body doesn’t even begin producing hCG until implantation is finished—most likely 8 – 10 days after conception. Once it does, the hormone doubles roughly every 48 hours.

Not all pregnancy tests are created equal. Here are some of the best pregnancy tests on the market. If you’ve ever stood in the pharmacy and examined all the different packets of tests, you’ve probably noticed that they’re usually sold in pairs, for a good reason. No matter what result you get from the first test, you should always test again two days later. If the second test shows a negative after a positive, it’s likely you’ve had a chemical pregnancy. If you get a positive result after a negative one, your body has produced enough hCG for the test to read it.

And, finally, if you get a positive after a positive—it’s time to make an appointment with your doctor.


*Note that studies approximate when implantation occurs based on the first appearance of chorionic gonadotropin in maternal urine.

View sources

Non-invasive imaging of human embryos before embryonic genome activation predicts development to the blastocyst stage

Time of Implantation of the Conceptus and Loss of Pregnancy

Vaginal bleeding in very early pregnancy

Urinary hCG patterns during the week following implantation

Lindsay Meisel

Lindsay Meisel is the Head of Content at Ava. She has over a decade of experience writing about science, technology, and health, with a focus on women's health and the menstrual cycle. Her work has been featured on The Fertility Hour, The Birth Hour, The Breakthrough Journal, and The Rumpus.

Related posts

Related posts

By continuing to use the site, you agree to the use of cookies. More information Accept

This site is using first and third party cookies to be able to adapt the advertising based on your preferences. If you want to know more or modify your settings, click here. By continuing to use the site, you agree to the use of cookies.