Pregnancy Conception Calculator
Estimate when conception occurred based on your due date or last menstrual period
Enter your estimated due date from your healthcare provider or ultrasound
Enter the first day your last period started
Normal range is 21-45 days. Default is 28 days.
Estimated Conception Date
Conception Window
Based on sperm survival of 3-5 days and egg viability of 12-24 hours, conception could have occurred within this window:
Earliest
Latest
Possible Intercourse Dates
Intercourse on any of these dates could have led to conception:
Day of ovulation 1 day before
Last Menstrual Period
First day of last period
Estimated Due Date
40 weeks from LMP
Current Gestational Age
weeks, days
Based on the calculated timeline
Pregnancy Timeline
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About Pregnancy Conception Calculator
The Pregnancy Conception Calculator helps you estimate when conception likely occurred. This is useful for understanding your pregnancy timeline, determining paternity, or satisfying curiosity about when your baby was conceived.
How Conception Date is Calculated
From Due Date (Reverse Calculation)
If you know your estimated due date:
Formula: Conception Date = Due Date - 266 days (38 weeks)
This works because:
- Full-term pregnancy is 280 days from LMP
- Conception typically occurs 14 days after LMP
- Therefore, conception to birth is approximately 266 days
From Last Menstrual Period
If you know your LMP:
Formula: Conception Date = LMP + (Cycle Length - 14) days
For a standard 28-day cycle, conception typically occurs around day 14.
Understanding the Conception Window
Conception isn't an instantaneous event. The conception window typically spans 5-6 days because:
- Sperm survival: Sperm can live inside the female body for 3-5 days
- Egg viability: The egg is viable for only 12-24 hours after ovulation
- Fertilization timing: Intercourse days before ovulation can still lead to pregnancy
| Factor | Duration |
|---|---|
| Sperm survival | 3-5 days |
| Egg viability | 12-24 hours |
| Fertile window | 5-6 days |
Important Accuracy Considerations
- Ultrasound dating: Early ultrasounds provide the most accurate due date
- Cycle variations: Irregular cycles affect LMP-based calculations
- Ovulation timing: Not everyone ovulates on day 14
- Medical confirmation: Always consult your healthcare provider for accurate dating
Frequently Asked Questions
Q: Can I determine the exact day of conception? A: No, you can only estimate a conception window. Sperm can survive several days, so the exact moment of fertilization cannot be pinpointed.
Q: Is the conception date the same as the intercourse date? A: Not necessarily. Conception can occur up to 5 days after intercourse due to sperm survival.
Q: How accurate is this calculator? A: This provides an estimate within a 5-6 day window. For precise dating, early pregnancy ultrasound is most accurate.
Disclaimer: This calculator provides estimates only. Consult your healthcare provider for accurate pregnancy dating and medical advice.
Understanding Conception
From Due Date Formula
Conception Date = Due Date - 266 days (38 weeks)
This is the reverse of the standard pregnancy calculation
From LMP Formula
Conception Date = LMP + (Cycle Length - 14) days
Ovulation typically occurs 14 days before the next period
💡 Important Notes
- Sperm can survive 3-5 days inside the body, so the exact intercourse date may differ
- The egg is only viable for 12-24 hours after ovulation
- Early ultrasound provides the most accurate pregnancy dating
- This calculator provides estimates only - consult your healthcare provider