1. What is LMP Pregnancy Calculator?

The LMP (Last Menstrual Period) Pregnancy Calculator estimates the due date and current gestational age based on the first day of your last menstrual period using Naegele's rule.

2. How Does the Calculator Work?

The calculator uses the standard obstetric formula:

Where:

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

Explanation: This calculation follows Naegele's rule, which adds 7 days to the LMP date, then subtracts 3 months, and finally adds 1 year.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for prenatal care planning, monitoring fetal development, scheduling important tests, and preparing for delivery.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period in the date field. Ensure the date is accurate for the most precise due date estimation.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the LMP method?
A: The LMP method is generally accurate within ±2 weeks when the menstrual cycle is regular (28 days).

Q2: What if my cycle is irregular?
A: For irregular cycles, ultrasound dating in the first trimester is more accurate for determining gestational age.

Q3: Why 280 days instead of 9 months?
A: Pregnancy is calculated as 40 weeks (280 days) from LMP, which is approximately 9 calendar months plus 1 week.

Q4: When should I confirm with ultrasound?
A: An early ultrasound (8-12 weeks) can provide the most accurate dating and should be used to confirm or adjust the LMP-based due date.

Q5: What percentage of babies are born on their due date?
A: Only about 5% of babies are born exactly on their due date. Most are born within 2 weeks before or after.