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LMP Calculation Formula:
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The LMP (Last Menstrual Period) based due pregnancy calculation estimates the date of the last menstrual period from the estimated due date. This method uses the standard pregnancy duration of 280 days (40 weeks) from LMP to EDD.
The calculator uses the simple formula:
Where:
Explanation: This calculation works backward from the estimated due date to determine when the last menstrual period likely occurred, based on the standard 40-week pregnancy timeline.
Details: Calculating LMP from EDD is useful for verifying pregnancy dating, understanding conception timing, and providing important reference points for prenatal care and fetal development tracking.
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 (40 weeks).
Q1: Why is 280 days used as the standard pregnancy duration?
A: 280 days (40 weeks) is the traditional calculation based on the average human gestation period from the first day of the last menstrual period.
Q2: How accurate is this calculation?
A: This provides an estimate. Actual pregnancy duration can vary, and ultrasound measurements often provide more precise dating, especially in early pregnancy.
Q3: What if I know my conception date instead of EDD?
A: If you know the conception date, LMP is typically about 2 weeks before conception, and EDD is about 38 weeks from conception.
Q4: Why calculate LMP from EDD instead of the other way around?
A: This reverse calculation is useful when you have an estimated due date (from ultrasound or healthcare provider) but need to determine the corresponding LMP for records or verification.
Q5: Are there factors that can affect this calculation?
A: Yes, irregular menstrual cycles, uncertainty about dates, and individual variations in gestation can affect accuracy. Always consult with healthcare providers for precise dating.