Dating uncertainty
Conception timing varies with cycle length, ovulation timing and dating method. Ultrasound and clinical history can change pregnancy dating.
Example
A due date estimate is often counted from pregnancy dating conventions, not from a known exact conception moment. Working backward from a due date gives an approximate window rather than one certain day.
How to use the result
Use the window as a general planning estimate. If timing matters for medical, legal or personal reasons, discuss the dates with a qualified clinician.
Limitations
This calculator cannot confirm conception, paternity, gestational age or pregnancy status. Cycle irregularity, assisted reproduction, ultrasound findings and clinical history can change the estimate.
Last reviewed: 2026-05-17