1. How Pregnancy Duration is Calculated

Pregnancy duration is calculated as approximately 9 months (40 weeks) from the last menstrual period (LMP). This is based on the standard 280-day pregnancy calculation.

2. Understanding the Calculation

The calculator uses these formulas:

Where:

• LMP — First day of last menstrual period
• 280 days — Standard pregnancy duration (40 weeks)
• 30.42 — Average days in a month

Explanation: Pregnancy is typically counted from the first day of your last period because ovulation and conception dates are often unknown.

3. Importance of Accurate Dating

Details: Accurate pregnancy dating is crucial for proper prenatal care, timing of tests, and determining if the baby is growing appropriately.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period and the current date to calculate how far along you are and your estimated due date.

5. Frequently Asked Questions (FAQ)

Q1: Why is pregnancy calculated from LMP and not conception?
A: Most women know their LMP but not their conception date. Conception typically occurs about 2 weeks after LMP.

Q2: Is 40 weeks exactly 9 months?
A: Not exactly. 40 weeks is about 9.2 months, which is why pregnancy often extends slightly beyond 9 calendar months.

Q3: What if I don't know my LMP?
A: An ultrasound in early pregnancy can estimate gestational age based on fetal measurements.

Q4: Are all pregnancies exactly 280 days?
A: No, normal pregnancies can range from 37-42 weeks. First pregnancies often last longer.

Q5: Why use 30.42 days per month?
A: This accounts for the average month length (365.25 days/year ÷ 12 months = 30.44 days/month).