Implantation Calculator: Getting to the Bottom of the Dates

by Aug 6, 2019

If you think you are pregnant, you may wonder when implantation occurs. Implantation is a critical step of pregnancy, during which the fertilized egg attaches to the uterine lining. You’ll find plenty of calculators online that tell you your implantation time. But they often end up to be not accurate.

woman with an envelope and flowers

Here is how these calculators work. They assume implantation takes place 9 days after ovulation/fertilization. Here are two couple common ways to calculate your implantation date:

  • If you know your ovulation date, implantation date = ovulation date + 9 days
  • If you know the first day of your last menstrual period, implantation date = the first day of your last menstrual period + 23 days

The second method assumes a 28-day menstrual cycle and ovulation happens on day 14. Implantation date occurs 9 days after ovulation, so 14 days + 9 days = 23 days.

However, both methods are approved to be oversimplifying. Women’s health is regulated by hormones, which varies hugely from woman to woman and cycle to cycle. A 28 days menstrual cycle and ovulation happening on day 14 are just the averages. 

Tracking your ovulation and the fertile window is very valuable to understand when you ovulate specifically in this menstrual cycle. And then you can add 8-10 days to estimate when your implantation occurs.

Many women have more variable cycle length and ovulation timing than they may think. To precisely know your ovulation, try a fertility tracker such as Mira.


What is implantation?

The ovary releases a mature egg down to the fallopian tube during ovulation. If the egg meets sperm along the way, the union leads to fertilization. Implantation occurs when the fertilized egg attaches itself to the uterine wall and is considered as the beginning of pregnancy. 

This is the early stage of prenatal development. It can take place between 6 to 12 days after ovulation.

As soon as the implantation occurred, the pregnancy hormone hCG (human chorionic gonadotropin) rises in the mother’s blood. The hCG level in blood can be detected 3-4 days after implantation, followed by a urine test 1-2 days later. hCG indicates baby growth and pregnancy status during early pregnancy. It is commonly used by healthcare practitioners to assess your pregnancy health.

When does implantation occur?

For most women, implantation occurs between 7 to 11 days after ovulation. A study published in the New England Journal of Medicine has shown the estimated risk of early loss was strongly related to the time of implantation. They have found that the early loss was least likely when implantation occurred by the 9th day after ovulation. The risk increases with every additional day.

What are the implantation symptoms and signs?

Although many women don’t feel the implantation, a small percentage of women could find themselves bleeding or spotting during early pregnancy. You may also experience other implantation symptoms such as:

  • Cramps
  • Mood swings
  • Headaches
  • Breast swelling or tenderness

Implantation bleeding is often called implantation spotting. It usually doesn’t look like a regular menstrual period. It is usually brown or pink in color and happens about 9 days after ovulation when the egg attaches to the wall of the uterus. It can range between 6-12 days.

When can I get a positive pregnancy test?

To get an accurate result, you should wait until the week after your missed period. If you really want to see the result early, you should wait until at least two weeks after having sex to perform a home pregnancy test, assuming you have 28 days cycle.

The pregnancy test measured the hCG concentration of your body. And it takes time for your body to produce this hormone after implantation. If you feel implantation symptoms such as bleeding or spotting, cramp, or nausea, you could consider taking it earlier.

✔️ Medically Reviewed by Banafsheh Kashani, MD, FACOG

Banafsheh Kashani, MD, FACOGBanafsheh Kashani, M.D., FACOG is a board-certified OB/GYN and specialist in reproductive endocrinology and infertility at Eden Fertility Centers, and has been treatingcouples and individuals with infertility since 2014.

Dr. Kashani has conducted extensive research in female reproduction, with a specific focus on the endometrium and implantation.

Additionally, Dr. Kashani has authored papers in the areas of fertility preservation, and fertility in women with PCOS and Turners syndrome. She also was part of a large SART-CORS study evaluating the trend in frozen embryo transfers and success rates.

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