1. What is Reverse Due Date Calculation?

The reverse due date calculation estimates the conception date by subtracting 266 days (38 weeks) from the expected due date. This is based on the typical 40-week pregnancy duration minus the 2 weeks before conception in the pregnancy dating system.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Explanation: This calculation assumes a standard 28-day menstrual cycle with ovulation occurring on day 14, and that conception occurred within 24 hours of ovulation.

3. Importance of Conception Date

Details: Knowing the conception date can help estimate fetal age more accurately, which is important for prenatal care and developmental tracking.

4. Using the Calculator

Tips: Enter the expected due date (from ultrasound or last menstrual period calculation) to estimate when conception likely occurred.

5. Frequently Asked Questions (FAQ)

Q1: Why 266 days instead of 280?
A: Pregnancy is typically counted as 40 weeks from the last menstrual period (280 days), but conception occurs about 2 weeks after LMP, hence 266 days.

Q2: How accurate is this calculation?
A: It provides an estimate. Actual conception may vary by a few days depending on cycle length and ovulation timing.

Q3: Does this work for IVF pregnancies?
A: For IVF, the conception date is known precisely, so this calculator isn't needed.

Q4: What if my cycle isn't 28 days?
A: Women with longer or shorter cycles may need to adjust the calculation based on their typical ovulation day.

Q5: Can this determine paternity?
A: It provides an estimated conception window, but not precise enough for definitive paternity determination.