When does implantation happen?
After fertilisation, the embryo travels down the fallopian tube and implants in the lining of the uterus. A well-known study of naturally conceived pregnancies found that implantation happened between 6 and 12 days after ovulation, most often on days 8 to 10. The implantation calculator works out your ovulation date from your last period and cycle length (or uses your ovulation date directly) and adds those days.
Implantation window = ovulation + 6 to 12 days (most often + 8 to 10)
Implantation bleeding
Some people notice light spotting — pink or brown, much lighter than a period — around the time of implantation. Many people have no implantation bleeding at all, and spotting can have other causes. Heavy bleeding, bleeding with pain, or bleeding that worries you should always be checked by a healthcare professional.
Implantation and pregnancy tests
hCG, the hormone pregnancy tests detect, is produced only after implantation. Levels then rise over the following days, which is why a test taken right after implantation is usually still negative. The calculator shows the day your period is due — the most reliable day to test — and the Pregnancy Test Calculator explains early testing.
Implantation after IVF
After an embryo transfer, implantation usually starts within a few days, because a day-5 blastocyst is already at the stage where it can implant. Use the IVF Due Date Calculator for IVF dating.