Conception Calculator
Calculate your estimated conception date based on your due date.
Due Date Information
Please enter your due date
Conception Estimate
Enter your due date to calculate conception date
About This Calculator
The Conception Calculator helps you estimate when conception likely occurred based on your due date. Conception is when the egg is fertilized by sperm, which typically happens around the time of ovulation.
Pregnancy is typically calculated from the first day of your last menstrual period (LMP), which is about 2 weeks before conception. The calculator estimates conception date by working backwards from your due date.
Formula & Calculation Method
Conception Date Calculation:
Conception Date = Due Date - 266 days
(Pregnancy from conception is typically 266 days, or 38 weeks)
Alternative Calculation:
Conception Date = LMP + 14 days (average)
(Ovulation/conception typically occurs 14 days after LMP)
Conception typically occurs around the time of ovulation, which is usually about 14 days after the start of your last menstrual period. The calculator estimates conception by subtracting 266 days (38 weeks) from your due date, as pregnancy from conception averages 266 days.
How to Use This Calculator
- Enter Due Date: Input your estimated due date (from ultrasound or LMP calculation).
- View Results: See your estimated conception date based on the due date.
Frequently Asked Questions
How accurate is the conception date calculation?
The calculation provides an estimate. Actual conception can vary by a few days, as pregnancy duration varies and due dates are estimates. An early ultrasound (around 8-12 weeks) provides the most accurate dating.
What is the difference between conception date and due date?
Conception date is when the egg was fertilized (around ovulation). Due date is calculated from LMP or ultrasound and is typically about 266 days (38 weeks) after conception, or 280 days (40 weeks) after LMP.
Can I determine the exact day of conception?
It's difficult to determine the exact day without tracking ovulation. Conception can occur within a window of several days around ovulation. Sperm can survive up to 5 days, and the egg is viable for about 24 hours after ovulation.
Why is pregnancy counted from LMP and not conception?
Pregnancy is counted from LMP because it's easier to identify the start of the last period than the exact day of conception. This adds about 2 weeks to the pregnancy timeline, making a full-term pregnancy 40 weeks from LMP (38 weeks from conception).
NumCalculators Editorial Team
Multi-disciplinary Expert Team
The NumCalculators Editorial Team consists of subject matter experts across various fields who review and verify the accuracy of our calculators. Each calculator undergoes rigorous testing and validation before publication.