How To Calculate Weeks Pregnant From LMP

Weeks From LMP Formula:

\[ \text{Weeks From LMP} = \left\lfloor \frac{\text{Current Date} - \text{LMP}}{7} \right\rfloor \]

Weeks From LMP:

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1. What Is Weeks From LMP Calculation?

The Weeks From LMP calculation determines gestational age by calculating the number of weeks that have passed since the first day of the last menstrual period (LMP). This is the standard method used in obstetrics to date pregnancies.

2. How Does The Calculator Work?

The calculator uses the following formula:

\[ \text{Weeks From LMP} = \left\lfloor \frac{\text{Current Date} - \text{LMP}}{7} \right\rfloor \]

Where:

\( \text{LMP} \) — First day of last menstrual period
\( \text{Current Date} \) — Today's date or any specified date
\( \left\lfloor \cdot \right\rfloor \) — Floor function (rounds down to nearest whole number)

Explanation: The calculation finds the total days between LMP and current date, then divides by 7 to get weeks, rounding down to the nearest whole week.

3. Importance Of Pregnancy Dating

Details: Accurate pregnancy dating is essential for monitoring fetal development, scheduling prenatal tests, determining due date, and making clinical decisions throughout pregnancy.

4. Using The Calculator

Tips: Enter the first day of your last menstrual period and the current date (or any date you want to calculate from). The calculator will display the completed weeks of pregnancy.

5. Frequently Asked Questions (FAQ)

Q1: Why use LMP instead of conception date?
A: LMP is used because it's typically easier to recall than conception date and provides a standardized method for pregnancy dating across healthcare providers.

Q2: How accurate is LMP dating?
A: LMP dating is generally accurate for women with regular 28-day cycles. Ultrasound dating may be used if LMP is uncertain or cycles are irregular.

Q3: What if I don't know my exact LMP?
A: If LMP is uncertain, an early pregnancy ultrasound (first trimester) provides the most accurate dating for gestational age.

Q4: Does this work for IVF pregnancies?
A: For IVF pregnancies, gestational age is calculated from embryo transfer date plus 14 days (or from retrieval date plus 14 days for fresh transfers).

Q5: Why round down to whole weeks?
A: Rounding down to completed weeks follows standard obstetric practice where pregnancy is described in completed weeks and days (e.g., "12 weeks 3 days").