1. What is Reverse Due Date Calculation?

Reverse due date calculation estimates the conception date based on a known due date. This is useful for determining when pregnancy likely began when you know the expected delivery date.

2. How Does the Calculator Work?

The calculator uses the standard pregnancy duration:

Where:

• 266 days — Standard length of human pregnancy from conception
• Due Date — Estimated date of delivery (EDD)

Note: This assumes a standard 38-week pregnancy from conception (or 40 weeks from last menstrual period).

3. Importance of Knowing Conception Date

Details: Knowing the conception date can help with understanding pregnancy timing, determining paternity, and estimating fetal development milestones.

4. Using the Calculator

Tips: Enter the known due date in the format YYYY-MM-DD or use the date picker. The calculator will estimate when conception likely occurred.

5. Frequently Asked Questions (FAQ)

Q1: Why 266 days?
A: Human pregnancy typically lasts 266 days (38 weeks) from conception, or 280 days (40 weeks) from the last menstrual period.

Q2: Is this date always accurate?
A: This is an estimate. Actual conception may vary by a few days due to natural variation in pregnancy length and timing of ovulation.

Q3: What if I know my LMP date instead?
A: Conception typically occurs about 14 days after the first day of the last menstrual period (LMP) in a regular 28-day cycle.

Q4: Does this work for IVF pregnancies?
A: For IVF, the conception date is known precisely (embryo transfer date), making this calculation unnecessary.

Q5: Can this determine paternity?
A: It can estimate conception timing, but paternity depends on multiple factors including intercourse timing and fertility windows.