Due Date Calculator
Estimate due date from last menstrual period using the Naegele rule.
Use the calculator below, then review the formula, a numeric example, and the reference table to understand how the pregnancy due date calculator result is produced.
Calculator inputs
Result
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What is this calculator?
Estimate due date from last menstrual period using the Naegele rule. The formula, a worked example, and a reference table are below. Results are for education only, not medical advice.
How it works
Naegele rule: due date ≈ LMP + 280 days; gestational age from days since LMP.
Example
60 days since LMP about 8 weeks 4 days gestational; ~220 days until due date.
Reference Table
| Value | Meaning |
|---|---|
| LMP + 280 | Classic 40-week obstetric default |
| Ultrasound | Often refines dating |
| IVF | Embryo age may differ from LMP |
FAQ
How accurate is LMP dating?
Irregular cycles reduce accuracy.
When is ultrasound used?
Early scans can adjust the due date.
Preterm signs?
Regular contractions or bleeding need assessment.
Why 280 days?
40-week convention from LMP.