Estimate the probable conception window from a birth or due date.
Gestational age is counted from the last period while conception occurs about two weeks later, which is why the two differ by a fortnight. Sperm survival widens the probable conception window to about six days. This arithmetic can only ever indicate a window, and DNA testing is the only reliable means of establishing paternity.
Paternity
Conception occurs about two weeks after the last period, so gestational age less 14 days
This calculation indicates an approximate conception window only and cannot establish or exclude paternity. Only accredited DNA testing can determine paternity, and legal paternity is a separate question governed by local law. Seek qualified legal and medical advice.
Conception occurs about two weeks after the last period, so gestational age less 14 days Gestational age is counted from the last period while conception occurs about two weeks later, which is why the two differ by a fortnight. Sperm survival widens the probable conception window to about six days.
This arithmetic can only ever indicate a window, and DNA testing is the only reliable means of establishing paternity.
This calculator takes 3 inputs: Gestational age at birth, Days since birth, Typical cycle length. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.