Fertility Tool

Conception Date Calculator

Work backward from your due date to find your likely conception date, estimated implantation window, and earliest positive test date.

100% Private Instant Results Medically Reviewed
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Calculate Conception Date

Don't know your EDD? Use our Due Date Calculator first.
Likely Conception Date
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Implantation Around
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hCG Detectable From
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Calculated using the standard 266-day gestation period from fertilization.

How Is Conception Date Calculated?

Conception (fertilization) occurs approximately 266 days before birth. Our calculator subtracts 266 days from your due date to estimate when fertilization likely occurred. This typically aligns with your fertile window in the cycle before your missed period.

Timeline After Conception

  • Day 0 — Fertilization: Sperm meets egg in the fallopian tube — a zygote is formed
  • Days 1–4 — Cell Division: Zygote divides rapidly, forming morula then blastocyst
  • Days 6–12 — Implantation: Blastocyst embeds into the uterine lining (may cause light spotting)
  • Days 10–14 — hCG Production: Embryo begins producing pregnancy hormone hCG
  • Day 14+ — Positive Test Possible: hCG levels high enough for home test detection

Conception vs. Gestational Age

When your doctor says "you are 6 weeks pregnant," they mean 6 weeks from your LMP — you've only been truly pregnant (post-fertilization) for about 4 weeks. This 2-week difference is standard medical convention used worldwide.

Medical Disclaimer: This tool is for educational purposes only and should not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for personalized guidance.

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