everyday-health Verified Precision Tool
Pregnancy Due Date & Fertile Window Calculator
Calculate estimated due date using Naegele’s rule based on last menstrual period (LMP).
Mathematical Formula
Due Date = LMP + 1 Year - 3 Months + 7 Days
Overview & Explanation
Naegele’s rule estimates expected date of delivery assuming a standard 280-day gestation period from LMP.
How It Works
- Adds 280 days (40 weeks) to last menstrual period date.
- Adjusts for average cycle length.
Practical Applications
- Pregnancy milestone tracking.
- Trimester date estimation.
LMP January 1st
Calculate estimated due date.
1
Add 280 days to LMP
Jan 1 + 280 days
= October 8th
Frequently Asked Questions
How accurate is the estimated due date formula?
Fewer than 5% of babies are born precisely on their due date; most arrive within 2 weeks before or after.
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