About this Calculator
A standard human pregnancy lasts approximately 40 weeks (280 days) from the first day of the last menstrual period (LMP).
Formula & Calculations
Mathematical Formula
Due Date = LMP + 280 Days + (Cycle Length - 28 Days)
Naegele’s Rule adjusted day-for-day for cycle length variance.
How to Calculate Step-by-Step
1
Record LMP
First day of last menstrual period.
2
Adjust cycle
Apply offset if cycle is not 28 days.
3
Calculate EDD
Adds 280 days + cycle offset.
How to Use & Best Practices
Enter your LMP date and average cycle length.
Frequently Asked Questions
How accurate is a due date?
Only about 4% of babies are born precisely on their due date.