What is implantation?
After an egg is fertilised in the fallopian tube, it divides into a ball of cells (a blastocyst) and travels towards the uterus over several days. Implantation is when the blastocyst attaches to and burrows into the lining of the uterus. Once it does, the developing placenta begins producing hCG — the hormone pregnancy tests detect.
Research that tracked ovulation and hCG daily found that implantation usually happens 6 to 12 days after ovulation, most often around days 8 to 10. The calculator shows both the full window and the most likely days, based on your ovulation date or on your last period and cycle length.
Implantation timeline
| Days after ovulation | What typically happens |
|---|---|
| 0 | Ovulation; fertilisation can happen within about a day |
| 1–5 | The fertilised egg divides while travelling to the uterus |
| 5–6 | It reaches the uterus as a blastocyst |
| 6–12 | Implantation window (most often days 8–10) |
| 10–14 | hCG rises; sensitive tests may begin to detect it |
| ≈ 14 | Period due — most home tests are reliable |
Implantation bleeding and cramping
A minority of people notice light spotting around the time of implantation. It is typically pink or brown, light, and lasts from a few hours to a couple of days. Mild cramping can also happen. Because the same signs are common just before a period, they cannot confirm a pregnancy — only a test can. Heavy bleeding, bleeding with clots, or strong one-sided pain should always be checked by a healthcare professional.
When to test after implantation
It takes a few days after implantation for hCG to build up in urine. Testing on the day your period is due — about 14 days after ovulation — gives a reliable result for most people. The Pregnancy Test Calculator works out that date, and the Ovulation Calculator estimates ovulation if you are not sure of it.