Lunia · Free tools
Pregnancy Due Date Calculator
Estimate a due date from the first day of the last period and regular cycle length.
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How this calculator works
The period-based estimate adds 280 days to the last period start, then adjusts by usual cycle length minus 28 days. It assumes a regular ovulatory cycle and does not use ultrasound or embryo-transfer dating.
A worked example
First day of the last period: Aug 1, 2026 · Usual regular cycle length (days): 28
- Estimated due date
- May 8, 2027
- Dating basis
- First day of last period, adjusted for a 28-day cycle.
These are illustrative inputs, not personal recommendations.
Common questions
Why might my dating scan give a different date?
Ovulation timing and period recall can vary. A clinician may use ultrasound measurements to revise the estimate.
How should I use the result?
A due date is an estimate, not a predicted delivery day or confirmation of pregnancy. A dating scan can give a better estimate. Irregular cycles, uncertain period dates and fertility treatment need a different assessment.
Sources & method references
Formula-based results are estimates, not individual medical advice.