Due Date Recalculator (LMP vs Ultrasound)

Why are there two different due dates?

LMP assumes a standard 28-day cycle and ovulation around day 14. Ultrasound uses your baby’s measurements. A small shift between the two is common and does not automatically mean something is wrong.

Which due date should I trust more?

In many cases an early ultrasound due date is considered **more reliable** than LMP, especially if your cycles are not exactly 28 days. Always follow the due date and advice given by your care team.

What does the combined arrival window mean?

It is a **planning window** that spans both 7-day ranges around each due date. It is not a guarantee, just a way to see a realistic cluster of dates for packing, leave and support.

Can I use this to argue for changing my official due date?

No. Only your care provider can decide which due date to use in your notes. You can show them the difference, but they will base decisions on scan reports and clinical judgement.

What if the difference is more than a week?

Larger shifts can happen, especially if LMP was uncertain or cycles are very long or short. The tool will note that ultrasound may be more reliable for planning, but you still need to follow your provider’s guidance.

Does the tool use my cycle length?

No. It always uses **LMP + 280 days** for the LMP-based date and the ultrasound due date exactly as entered. It does not ask for or adjust by cycle length.