When does implantation happen?

Enter the first day of your last period or your estimated ovulation date.

First day of last period
Average cycle length28 days
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Implantation timing varies between people (6–12 days post-ovulation). These are estimates. Learn more
For reference only. Confirm pregnancy with a βhCG blood test and see an obstetrician for medical advice.

How is it calculated?

Implantation timing follows Wilcox 1999 — about 84% of normal pregnancies implant between days 8 and 10 after ovulation, with nearly all falling within days 6-12.

Formula: estimated implantation = ovulation day + 8-10 days (or LMP + ~22-24 days for a 28-day cycle). hCG only starts to be detectable 1-2 days after implantation.

Limitations of this estimate

This is a statistical average and individual variation is wide:

  • If the ovulation day is uncertain, the implantation estimate shifts by the same amount (LH strips / BBT can confirm).
  • Cycles that are not 28 days or that are irregular reduce accuracy.
  • Implantation bleeding occurs in only 15-25% of pregnancies — its absence is normal.
  • Late implantation (day +11-12 after ovulation) is associated with a slightly higher risk of early miscarriage (Wilcox 1999).
  • This tool does not diagnose pregnancy — the OB-GYN blood βhCG is the standard.

Sources

Frequently asked

How do I tell implantation bleeding from a period?

Implantation bleeding is usually very light (a spot or two), pink to brown, and stops within 1-3 days. A regular period typically starts light, grows heavier, turns bright or dark red, and lasts 3-7 days.

There is no 100% reliable way to tell them apart and only about 15-25% of pregnancies show implantation bleeding — so its absence does not rule out pregnancy. If unsure, test from one week after the missed period or get a blood βhCG at your OB-GYN.

How many days after implantation can I test?

hCG only becomes detectable 1-2 days after implantation. That means a 10-20 mIU/mL early-detection strip can read positive from about ovulation +10-12 days (around the expected period day), but with a higher false-negative rate.

All OTC strips reach ≥99% accuracy one week after the missed period. The most accurate test is a blood βhCG at the OB-GYN.