Pregnancy Due Date Calculator (Naegele's Rule) Online Free
Enter the first day of your last menstrual period (LMP) — or a known estimated delivery date — plus average cycle length to get Naegele’s-rule EDD, current gestational age (weeks + days), trimester stage, percent of 40 weeks elapsed and a milestone timeline from first trimester through full term. Cycle length adjusts the classic 280-day gestation. Dates stay on your device; nothing is uploaded.
Pregnancy Due Date Calculator (Naegele's Rule) In-Browser Workspace
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How to Use Pregnancy Due Date Calculator (Naegele's Rule)
- Step 1: Enter the first day of the last period (LMP) in the date field.
- Step 2: Pick average cycle length (21–35 days); 28 is the standard default.
- Step 3: Alternatively paste a known due date and leave LMP empty.
- Step 4: Click Calculate Due Date to see EDD, gestational age and trimester.
- Step 5: Review milestone dates (13w, 20w, 28w, 37w, 40w) and days remaining.
About Pregnancy Due Date Calculator (Naegele's Rule)
Naegele’s rule estimates delivery 280 days (40 weeks) from the first day of the last menstrual period, because ovulation is often assumed ~14 days before the next period in a 28-day cycle. Irregular cycles shift ovulation, so many calculators add (cycle_length − 28) days: gestation_days = 280 + (cycle − 28). Gestational age counts from LMP, not conception — clinicians date pregnancies the same way. Trimesters are conventionally weeks 1–13, 14–27 and 28–40+. Only about 5% of pregnancies deliver on the exact EDD; the normal window is roughly 37–42 weeks (full term), so “days remaining” is a planning estimate, not a countdown clock. Working backward from a known EDD recovers LMP as EDD − (280 + cycle_offset). Ultrasound dating in the first trimester is more precise than LMP when periods are irregular, breastfeeding, or postpartum. This calculator does not detect pregnancy, fertility or complications — only calendar arithmetic from the dates you provide.
Frequently Asked Questions
How accurate is the due date?
Only ~5% deliver on the exact date. Most arrive within 37–42 weeks; ultrasound dating can shift EDD by several days.
Why add cycle length?
Longer or shorter cycles shift ovulation. Adding (cycle − 28) to the 280-day baseline better matches non-28-day cycles.
Can I enter a known due date instead of LMP?
Yes — leave LMP empty and enter EDD; the tool back-calculates LMP and gestational age.
Is this medical advice?
No. It is a calendar estimate. Confirm dating, growth and any symptoms with your healthcare provider.
Are my dates stored?
No — calculations run entirely in your browser and are not uploaded.