1. What is the Due Date Calculator?

The Pregnancy Due Date Calculator estimates the expected delivery date based on the last menstrual period (LMP) using the standard MedCalc formula of LMP + 280 days (40 weeks).

2. How Does the Calculator Work?

The calculator uses the standard obstetric formula:

Where:

• LMP — First day of last menstrual period
• 280 days — Standard duration of pregnancy (40 weeks)

Explanation: This calculation is based on Naegele's rule, assuming a 28-day menstrual cycle with ovulation occurring on day 14.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for prenatal care scheduling, monitoring fetal development, and determining if pregnancy is progressing normally.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period (LMP) in the format YYYY-MM-DD. The calculator will add 280 days (40 weeks) to determine the estimated due date.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this due date calculation?
A: Only about 5% of women deliver on their exact due date. Most deliver within 2 weeks before or after.

Q2: What if my cycle isn't 28 days?
A: For women with longer or irregular cycles, the due date may need adjustment based on early ultrasound dating.

Q3: Why 280 days if pregnancy is 9 months?
A: Pregnancy is actually about 9.5 months (40 weeks) when counted from LMP, since conception typically occurs about 2 weeks after LMP.

Q4: How does this compare to ultrasound dating?
A: First-trimester ultrasound is more accurate and becomes the standard if there's more than 5-7 days difference from LMP dating.

Q5: What's the margin of error?
A: The standard deviation is ±14 days, meaning about 68% of women deliver within 2 weeks of their due date.