Naegele Pregnancy Due Date
Compute the estimated date of delivery from the first day of the last menstrual period using Naegele's rule: LMP + 280 days (40 weeks).
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Last menstrual period
- 2025-01-01
Result: Due date 2025-10-08
The tool opens with these values already filled in. Replace them with your own.
What you enter
- Last menstrual period (ISO date, YYYY-MM-DD)
What this is
Sophie Well returns the EDD plus the current gestational age in weeks and days, assuming a regular 28-day cycle and ovulation on day 14.
When to use it
Use this for an initial pregnancy-dating estimate when only the LMP is known. First-trimester crown-rump-length ultrasound is more accurate and should override Naegele if the dates differ by more than 5-7 days (ACOG/SMFM Committee Opinion 700); for IVF pregnancies, transfer-date dating supersedes both.
How this is calculated
Naegele rule: due date = LMP + 280 days.
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.
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