1. What is Pregnancy Dating?

Pregnancy dating calculates how far along a pregnancy has progressed based on the first day of the last menstrual period (LMP). This is the standard method used by healthcare providers to track pregnancy progress.

2. How Pregnancy Calculation Works

The calculator uses the following calculation:

Where:

• \( LMP \) — First day of last menstrual period
• \( Current\ Date \) — Today's date or any specified date

Explanation: Pregnancy is calculated from the first day of your last period, not the date of conception. A full-term pregnancy is about 40 weeks (280 days) from the LMP.

3. Importance of Accurate Dating

Details: Accurate pregnancy dating is crucial for proper prenatal care, scheduling tests, and determining if the baby is growing appropriately. It also helps predict the due date.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period and the current date (defaults to today). The calculator will show how many weeks and days pregnant you are, plus your estimated due date.

5. Frequently Asked Questions (FAQ)

Q1: Why is pregnancy counted from LMP and not conception?
A: LMP is used because most women can recall this date, while conception date is often unknown. It provides a consistent starting point.

Q2: What if I don't know my LMP?
A: An ultrasound in early pregnancy can estimate gestational age based on fetal measurements.

Q3: Is 40 weeks exactly 9 months?
A: No, 40 weeks is about 9 months and 1 week. Pregnancy months are counted as 4 weeks each.

Q4: What if my cycle isn't 28 days?
A: The calculation assumes a 28-day cycle. If your cycle is significantly different, your provider may adjust your due date.

Q5: How accurate is the due date?
A: Only about 5% of women deliver on their exact due date. It's an estimate, with most births occurring within 2 weeks before or after.