Standard Rule: Conception = Due Date − 266 days
Fertile Window: Conception ± 2 days (sperm lifespan)
Conception Date Calculator 2025: Find the Exact Day Your Baby Was Conceived
Conception date is the day sperm met egg — usually **14 days after LMP**. Our calculator reverse-engineers it from **due date**, **LMP**, or **ultrasound** with **±2 day fertile window**.
How Conception Date Is Calculated
| Method | Formula | Accuracy |
|---|---|---|
| Due Date | EDD − 266 days | ±3 days |
| LMP | LMP + 14 days | ±5 days |
| Ultrasound | US Date − GA | ±1–2 days (1st trimester) |
Fertile Window Explained
- Sperm lives **up to 5 days**
- Egg viable **12–24 hours**
- Intercourse **5 days before ovulation** can result in pregnancy
- Peak fertility: **day before & day of ovulation**
Why Know Conception Date?
- Legal paternity windows
- Zodiac & Chinese gender chart fun
- Plan baby announcements
- Track early milestones
Ultrasound Accuracy
- 6–9 weeks: ±3–5 days
- 10–14 weeks: ±5–7 days
- After 20 weeks: ±10–14 days
Irregular Cycles?
Use **ultrasound** — LMP method assumes 28-day cycle with ovulation on day 14.
Limitations
- Not for IVF (known embryo transfer)
- Assumes singleton pregnancy
- Does not confirm paternity
Pro Tips
- Combine with Ovulation Predictor
- Mark fertile window on calendar
- Retest with early ultrasound
FAQs
Can conception be 5 days after intercourse? Yes — sperm waits for egg.
What if I have a 35-day cycle? Ovulation ~day 21 → use ultrasound.
Is the date exact? Estimated — sperm DNA test for 100% certainty.
Conclusion
Use our **2025 Conception Date Calculator** to pinpoint that magical moment. Pair with ultrasound for best accuracy.
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