It is common in pregnancy to hear one due date based on your last menstrual period (LMP) and another from an ultrasound report. This tool is designed to help you compare those dates and understand why a clinician may keep the original LMP date or switch to the ultrasound-based date.
It is especially useful for early scans, but it can also compare later ultrasound timing by applying wider discrepancy thresholds.
How to Use the Due Date Reconciliation Tool
To estimate which date is more reliable, this tool needs three pieces of information:
- Your Last Menstrual Period (LMP) Date: Enter the first day of your most recent period.
- Your Ultrasound Date: Enter the date on which the ultrasound was performed.
- Gestational Age from Your Scan Report: Enter the gestational age from the scan report in weeks and days, such as 8 weeks 3 days.
The tool compares the due date calculated from each method and applies common medical dating thresholds to show which date may be more appropriate to use.
How the Timing Matters
Ultrasound dating is usually most accurate in early pregnancy. That is why smaller discrepancies can matter more in very early scans, while later scans often require a bigger difference before a due date would be changed. Doctors generally rely most heavily on the earliest reliable dating information.
Why a Single, Official Due Date Is Important
A final due date becomes the anchor for the rest of pregnancy care. It helps guide the timing of screening tests, growth checks, and decisions later in pregnancy, such as how to manage a pregnancy that goes well past the due date.
Important Medical Notes
This tool is for educational purposes and shows how LMP and ultrasound dating can be compared. The final official Estimated Due Date is the one confirmed by your healthcare provider and recorded in your chart. Always follow your clinician's guidance for pregnancy dating and care.