Conception date calculator guide: what the 266-day estimate means

Use these tools while you read—keep the same LMP or ultrasound anchor your clinician documented.

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“Conception date” in everyday speech might mean sex timing, a positive ovulation test, or IVF fertilization day—each has different precision.

Many tools add about 266 days from a conception estimate to approximate an EDD. That is not the same arithmetic as LMP + 280, even when both seem plausible.

Use our calculator’s conception tab to compare scenarios, then confirm the anchor your clinician documents.

If you manage a chronic condition, bring your medication list to every visit—even if the topic page is about something unrelated like trimester milestones. Drug safety questions belong in a charted conversation, not a comment thread.

Nutrition pages should never shame food culture. If guidance here conflicts with your clinician’s advice for gestational diabetes, hypertension, or hyperemesis, follow the personalized plan—those conditions override generic tips.

This article is educational. It does not diagnose, treat, or triage emergencies. Always follow your licensed obstetric clinician, midwife, or local emergency guidance.