Free · Early pregnancy
Implantation Calculator
Implantation — the moment a fertilised egg attaches to the uterine lining — usually happens 6 to 12 days after ovulation. This calculator estimates your implantation window, peak day, and when any associated spotting is likely.
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What is implantation?
After fertilisation, the embryo travels down the fallopian tube over 5–6 days, becoming a blastocyst. It then burrows into the uterine lining — this is implantation. Only after implantation does your body start producing hCG, which is what a pregnancy test detects.
Symptoms of implantation
- Spotting: 15–25% of pregnancies show light pink or brown bleeding for 1–2 days. Much lighter than a period.
- Cramping: mild, pulling sensation in the lower abdomen.
- Breast tenderness: often the earliest noticeable change.
- Temperature dip then rise: if you track BBT, you may see a brief dip on the day of implantation.
Implantation bleeding vs period
- Timing: implantation bleeding happens 1–2 weeks before the expected period; period bleeding arrives on schedule.
- Colour: implantation is usually pink or brown; period bleeding turns bright red.
- Flow: implantation is spotting — not enough to fill a pad. Period is heavier.
- Duration: implantation lasts hours to 2 days; a period lasts 3–7 days.
When implantation happens too late
Implantation beyond day 12 is associated with slightly higher early miscarriage risk. If your positive test appears very faint past the 14-day mark, consider a follow-up at 18–20 days for reassurance.
Frequently asked questions
Does every pregnancy have implantation bleeding?
No. Only about a quarter of pregnancies show spotting. Absence of spotting is entirely normal.
Can I test for pregnancy immediately after implantation?
Not reliably. Wait at least 2–3 days after suspected implantation for a sensitive test, or 5–7 days for a standard test.
What if the spotting is heavy?
Heavy bleeding in early pregnancy requires evaluation — see your GP the same day to rule out miscarriage or ectopic pregnancy.
Can I feel implantation?
Some women feel a light pinching or twinge. Most women feel nothing at all.
How accurate is this calculator?
Accurate within a day if ovulation dates are known. Less precise for irregular cycles — pair with BBT or ovulation tracking.
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Calculations based on standard obstetric formulas and WHO guidance. For medical decisions, always consult your doctor or midwife.