Implantation calculator

Enter the first day of your last period or your ovulation date. You will see when implantation is most likely, the full window and the day to take a pregnancy test. Your dates stay in your browser.

Your dates

First day of your last period Use the first day of your most recent period, the day full bleeding began.

Average cycle length Count from day 1 of one period to day 1 of the next. 28 days is a common starting point.

Adjust days between ovulation and your next period

Luteal phase length 14 days suits most people. Change it only if you have tracked a different pattern.

Dates stay in your browser. We never receive them.

Example: a 28-day cycle

Pick a date to see your own implantation window

In a 28-day cycle, ovulation falls around cycle day 15. Implantation is most likely 8 to 10 days later, on cycle days 23 to 25, and the full window runs from day 21 to day 27. Your dates replace this as soon as you enter them.

Ovulation
Implantation window, days 6 to 12
Most likely, days 8 to 10
Period due

Most likely8 to 10 days after ovulation

Full window6 to 12 days after ovulation

Test fromThe first day of a missed period

Implantation is most likely 8 to 10 days after ovulation. The full window runs from , 6 to 12 days after ovulation. In the study behind these numbers, 84% of pregnancies that continued implanted on days 8 to 10.

Estimated ovulation

Test from

Where you are today

Day by day after ovulation

Ovulation
Implantation window
Most likely days
Period due

More pregnancy calculators

See all pregnancy calculators

How the implantation window is worked out

1Find your ovulation day Next period minus 14 days Ovulation tends to happen about 14 days before your next period starts. Enter your cycle length and the calculator counts from your last period, or enter an ovulation date you already have.
2Add 6 to 12 days Ovulation + 6 to 12 days Implantation happens 6 to 12 days after ovulation, and in most pregnancies that continue it falls on day 8, 9 or 10. The calculator shows the full window and the most likely days.
3Pick your test day Next period due A pregnancy test is most reliable from the first day of a missed period. The calculator shows that date from your cycle, so you know when to test.

What these dates can and cannot tell you

The window is a good guide to when to expect spotting and when to test. It is an estimate, because ovulation and implantation both vary.

What the calculator uses

The first day of your last period and your usual cycle length, or an ovulation date.
A luteal phase of 14 days, which you can change from 10 to 16 days.
The timing from a 1999 study of 221 women who tested their urine every day.

What it cannot tell you

Show when your own implantation happened. That takes daily hormone testing, and it varies from one pregnancy to the next.
Know your ovulation day unless you enter a measured one. From a period date it uses a standard formula that has not been checked against measured ovulation.
Tell you whether you are pregnant. A test does that, and implantation can happen without any sign.
Estimate implantation after IVF, where timing depends on the embryo’s age and your clinic’s protocol.

When does implantation happen?

After an egg is fertilized, it divides as it travels toward the uterus. Implantation is when the ball of cells attaches to the lining of the uterus. It is the point at which the pregnancy hormone hCG starts to be made, which is why a pregnancy test cannot turn positive before it.

The timing comes from a study in the New England Journal of Medicine that followed 221 women who were trying to conceive. They collected urine every day for up to six months, so the researchers could find ovulation and the first day hCG appeared. In the 141 pregnancies that lasted past six weeks, hCG first appeared 6 to 12 days after ovulation, and 84% implanted on day 8, 9 or 10.

Woman writing on a paper wall-style calendar with a blue pen to mark important dates — Marking ovulation and test dates on a calendar. Photo by RDNE Stock project on Pexels.

Days past ovulation	What is happening	Your dates
0	Ovulation: an egg is released.	Enter a date above
0 to 1	Fertilization, if sperm are present. An egg can be fertilized for about 12 to 24 hours after it is released.	Enter a date above
1 to 5	The fertilized egg divides and travels toward the uterus. By about day 5 it is a hollow ball of cells called a blastocyst.	Enter a date above
6 to 12	Implantation window: the embryo attaches to the lining of the uterus, and hCG starts to be made.	Enter a date above
8 to 10	The most common days. In the study, 84% of pregnancies that continued implanted on day 8, 9 or 10.	Enter a date above
Day 14 on average	Your next period is due. This is the first day of a missed period and the day most tests become reliable.	Enter a date above

These are days past ovulation, often written DPO. If you count from your period instead, the calculator estimates ovulation first, so the dates move if your ovulation does.

Implantation bleeding and symptoms

A few people notice light spotting or a mild twinge around implantation, and most notice nothing at all. If spotting happens, it falls in the same 6 to 12 day window as implantation. It is usually lighter than a period and often pink or brown. A lack of spotting says nothing about the pregnancy.

Our guide to implantation bleeding compares it with an early period and lists other causes of light bleeding. Bleeding that is heavy, bright red or painful needs a call to your provider the same day.

When to take a pregnancy test

Implantation starts hCG production, and the hormone then has to build before a home test can detect it. That is why the day of implantation is not the day to test. The NHS advises testing from the first day of a missed period, and at least 21 days after the last unprotected sex if you do not know when your period is due.

The calculator shows the first day of a missed period as your test day. A blood test detects smaller amounts of hCG than a urine test. Our guide to when to take a pregnancy test explains how to get a reliable result, and the hCG calculator helps with a blood test result. Once you have a positive test, the due date calculator works out your due date.

What if it is earlier or later than the calculator says?

Ovulation can happen earlier or later than a formula predicts, so the whole window moves with it. If your cycles vary by more than a few days, use ovulation tests and enter the ovulation date they point to. Our best time to get pregnant calculator shows how to estimate your fertile window, and the signs of ovulation guide covers the clues.

In the 1999 study, pregnancies that implanted later were more likely to end early. A calendar cannot tell you when your own implantation happened, and a later positive test can come from later ovulation, a less sensitive test or later implantation. Early losses are common and are rarely caused by anything you did.

IVF and fertility treatment. This calculator is for natural conception. After IVF, timing depends on the age of the embryo at transfer and on your clinic's protocol, and published estimates vary, so follow the test date your clinic gives you.

Common questions

Short answers about implantation timing, bleeding and testing.

How do I calculate my implantation date?

Add 6 to 12 days to your ovulation day. If you only know your last period, subtract 14 days from your cycle length to find ovulation. In a 28-day cycle ovulation falls around cycle day 15, so implantation is most likely on cycle days 23 to 25 and the full window is days 21 to 27. The calculator above does the counting.

How many days after ovulation does implantation happen?

Between 6 and 12 days. In a 1999 study of 141 pregnancies that lasted past six weeks, hCG first appeared 6 to 12 days after ovulation, and 84% implanted on day 8, 9 or 10.

When does implantation bleeding happen?

If it happens, it falls in the same 6 to 12 day window. It is light, often pink or brown, and it is lighter than a period. Many people have no bleeding at all, and having none says nothing about the pregnancy. Our guide to implantation bleeding explains how to tell it from an early period.

How soon after implantation can I take a pregnancy test?

Implantation starts hCG production, and the hormone then needs time to build before a home test detects it. The NHS advises testing from the first day of a missed period, and a blood test can detect smaller amounts than a urine test. The calculator shows the first day of a missed period as your test day.

Can implantation happen 5 days after ovulation?

In the 1999 study, hCG first appeared on day 6 at the earliest in the pregnancies that continued, so implantation before day 6 is unlikely. Your ovulation day may also be a few days off from the calculator’s estimate, which moves the count.

Is 14 days past ovulation too late for implantation?

In the pregnancies that lasted past six weeks, hCG first appeared by day 12 after ovulation. A positive test at 14 days past ovulation is typical timing, because the hormone has had a couple of days to build.

What if I do not know when I ovulated?

Enter the first day of your last period and your usual cycle length. The result is an estimate, so treat the window as a guide that could shift by a few days. Ovulation tests can narrow it, and you can enter the date they point to using the ovulation date option.

Is the window different with irregular cycles?

Yes. A period-based estimate assumes you ovulate 14 days before your next period, and that assumption is weaker when cycles vary. Use ovulation tests and the ovulation date option, or talk to your provider about why your cycles change.

Is late implantation a bad sign?

In the 1999 study, pregnancies that implanted later were more likely to end early. You cannot tell from a calendar when your own implantation happened, and a later positive test can reflect later ovulation, a less sensitive test or later implantation. Early losses are common and are rarely caused by anything you did.

Can you feel implantation?

Most people feel nothing. Some notice a mild twinge, light cramps or a little spotting. These feelings also happen before a period, so they cannot confirm anything on their own.

Is there an implantation calculator for IVF?

This one is for natural conception. After IVF, timing depends on the age of the embryo at transfer and on your clinic’s protocol, and published estimates vary. Follow the test date your clinic gives you.

What does DPO mean?

Days past ovulation. Day 0 is the day of ovulation, so 9 DPO is nine days after it.

Does the calculator save my dates?

No. They stay in your browser and are never sent to us. A session store in your own tab keeps them until you close the tab, so you can move between calculators.