1. What is LMP Reverse Calculation?

The LMP (Last Menstrual Period) Reverse calculation determines the start date of the last menstrual period based on the estimated due date (EDD). This is useful for confirming pregnancy dating and understanding gestational age.

2. How Does the Calculator Work?

The calculator uses the standard pregnancy calculation:

Where:

• \( LMP \) — Last Menstrual Period date
• \( EDD \) — Estimated Due Date
• \( 280 \) — Standard duration of pregnancy in days (40 weeks)

Explanation: This calculation assumes a standard 40-week pregnancy duration from the first day of the last menstrual period.

3. Importance of LMP Calculation

Details: Accurate LMP dating is crucial for proper prenatal care, scheduling ultrasounds, monitoring fetal development, and determining gestational age for delivery planning.

4. Using the Calculator

Tips: Enter the estimated due date in the date field. The calculator will automatically compute the corresponding last menstrual period date by subtracting 280 days.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract 280 days?
A: 280 days represents the standard 40-week duration of pregnancy calculated from the first day of the last menstrual period.

Q2: Is this calculation always accurate?
A: While this is the standard calculation, individual pregnancies may vary. Ultrasound dating in the first trimester is more accurate for establishing gestational age.

Q3: What if I know my conception date?
A: If conception date is known, LMP is typically about 14 days before conception for women with regular 28-day cycles.

Q4: Can this be used for irregular cycles?
A: For women with irregular cycles, this calculation may be less accurate. Ultrasound dating is recommended in such cases.

Q5: How is this different from Naegele's rule?
A: This is essentially the reverse of Naegele's rule, which calculates EDD from LMP by adding 280 days.