Conception Date Calculator
Enter the first day of last menstrual period (LMP) and cycle length to estimate the conception date and due date (Naegele's rule).
Input Data
First day of last menstrual period
Average cycle length (default 28)
Results
Estimated date of conception
2026-01-15
Estimated due date (EDD)
2026-10-08
Approximate weeks of gestation today
34.6
LMP 2026-01-01 -> conception ~ 2026-01-15; due 2026-10-08 (~34.6 weeks).
At a glance:Conception ~ LMP + 14 days; due date = LMP + 280 days + (cycle-28) days (Naegele's rule); weeks = (today - LMP) / 7.
Formula
conception = LMP + 14 days.
due = LMP + 280 + (cycle - 28) days.
weeks = (today - LMP) / 7.
How to Use
- Pick the first day of your last menstrual period and your cycle length.
- Get the approximate conception date, due date and current weeks.
Case Studies
LMP 2026-01-01, cycle 28
Conception ~ 2026-01-15; due date = 2026-10-08.
FAQ
Is the conception date exact?
It is an estimate; actual ovulation and fertilization can vary by several days. Early ultrasound is most accurate.
How does this differ from the Due Date Calculator?
This tool focuses on the conception date while also giving the due date.
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References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.