Practical tools for measured work
Last-period due-date estimate
Estimate a due date from a known last menstrual period and regular 28-day cycle using the 280-day convention.
How it works
Add 280 calendar days to the first day of the last menstrual period. This convention assumes a regular 28-day cycle and does not account for variation in ovulation.
Before using the result
- Check the selected mode, units and input values before using the result.
- Read the assumptions and rounding rules; compare the worked example with your intended calculation.
- A numerical result does not supply missing context or change the stated limitations.
Limitations
This is an estimate, not a predicted delivery day. Ultrasound, uncertain dates, irregular cycles and assisted reproduction may require different clinical dating. A clinician establishes or revises the obstetric due date. Do not use this calculator to delay care.
Frequently asked questions
What should I verify before using this result?
Check the input values, units, dates and assumptions. Compare the method and its stated limits with the source relevant to your task.
Why might the finished result differ?
Results depend on the entered data and the model’s assumptions. Rounding, changing conditions or omitted factors can affect the comparison. Read the limitations before using the result.
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