Use this quick tool to compare light bleeding/spotting to your implantation window and cycle timing. It provides a simple likelihood (implantation vs period) and suggests when to test next. This is educational only and not medical advice.
Methodology & limits
What this estimates
This tool compares two rule-based scores, “implantation” vs “period”, using timing against the implantation window plus bleeding features (spotting vs flow, pad or tampon use, cramps, clots). Scores are normalised to show a relative likelihood. This is not a diagnosis.
Timing model
If ovulation is known, we compute days-past-ovulation (DPO) and apply a peaked weight that is highest near 9 DPO and tapers toward 4 and 14 DPO. This follows prospective urinary-hCG work showing most successful implantations occur about 8–10 DPO (plausible range 6–12 DPO) NEJM 1999. If ovulation is unknown, we estimate ovulation from cycle length and the expected period date, informed by day-specific fecundability patterns around ovulation NEJM 1995.
Bleeding pattern heuristics
Implantation bleeding is usually light and brief. The model up-weights spotting and no product use, and down-weights heavier flow, clots, and severe cramps, which more often align with menstruation or non-viable early pregnancy bleeding. Heuristics are based on prospective early-pregnancy cohorts and clinical descriptions of early bleeding patterns.
Testing guidance
If ovulation is known, test at 10 DPO or later; otherwise test on the expected period date. If negative, retest after about 48 hours because early hCG rises can be missed and some home tests only detect around 25 mIU/mL in practice Clin Chem Lab Med 2014.
Clinical safeguards
Heavy bleeding, severe or one-sided pain, dizziness, shoulder pain, or fainting need urgent care to rule out miscarriage or ectopic pregnancy. See guidance from ACOG and NICE NG126.
Disclaimer
Educational information only, not medical advice. For personal recommendations, speak with a clinician.
What’s next?
Urgent? If you’re within 120 hours (5 days) of sex, see Morning-After Pill Effectiveness.
What this calculator can (and can’t) tell you
- It’s a quick screen, not a diagnosis. Results combine simple rules with your cycle timing and reported bleeding pattern.
- Implantation timing is narrow. Most implantation occurs ~6–10 days after ovulation; spotting, if present, is usually light and brief (often <48 hours).
- Period clues: steady flow that needs pads/tampons, cramps, and clots usually point to a period rather than implantation.
Reading your result
- “More likely implantation” → wait until the first reliable test day from the app, or test now with the understanding early negatives are common.
- “More likely period” → if bleeding behaves like your usual period, testing immediately may be negative; retest if cycles are irregular or symptoms change.
If bleeding is heavy, prolonged, or painful, seek medical care. This tool cannot evaluate ectopic pregnancy or other urgent conditions.
Implantation Bleeding FAQ
How long does implantation bleeding last?
Usually short—often a few hours up to 1–2 days. Persistent or heavy flow fits a period more than implantation.
Can you have cramps with implantation?
Mild cramping can occur for some, but moderate to strong cramps are more typical of a period.
When should I take a test?
For the best chance of detection, test on or after the calculator’s suggested “best test day.” If negative but you still suspect pregnancy, retest 48–72 hours later.