Implantation Calculator — When Does Implantation Happen?

Calculate Implantation Date

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Date of ovulation

From OPK surge, BBT chart, or fertility monitor

First day of last period

We'll estimate ovulation from your cycle length

Date of embryo transfer

Average cycle length

Embryo age at transfer

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The Two-Week Wait Decoded

Enter your details to see your personalized implantation window, DPO symptom timeline, and when to test.

Understanding Implantation

What Is Implantation?

Implantation is when a fertilized egg (now a blastocyst) attaches to the uterine lining. This is the moment pregnancy truly begins — it triggers hCG production, which is what pregnancy tests detect. Without successful implantation, even a fertilized egg won't result in pregnancy.

When Does Implantation Happen?

After ovulation and fertilization, the blastocyst travels through the fallopian tube for several days before reaching the uterus. Implantation most commonly occurs between 8–10 days past ovulation (DPO), with the full possible range being 6–12 DPO. Research from a 1999 NEJM study found:

6 DPO: ~0.5% of implantations
7 DPO: ~5% of implantations
8 DPO: ~18% of implantations
9 DPO: ~36% — most common single day
10 DPO: ~27% of implantations
11 DPO: ~10% of implantations
12 DPO: ~4% of implantations

Implantation Bleeding vs. Period

About 25–30% of women experience light spotting around implantation. Here's how to tell the difference:

Color: Implantation bleeding is typically light pink or brown, not bright red
Flow: Very light spotting or a few drops — never enough to fill a pad
Duration: Lasts 1–2 days, versus 4–7 days for a period
Timing: Occurs before your expected period date

What About IVF Transfers?

For IVF, implantation timing is calculated from the transfer date and the embryo's age. A Day 5 blastocyst is already further developed, so implantation typically occurs 1–5 days after transfer. A Day 3 embryo needs extra development time, so implantation usually happens 3–7 days after transfer.