NHS conception correlation and dating scans
Under NHS guidance, healthcare professionals date pregnancies from the first day of the last period rather than conception date, as period onset is an observable physical event.
However, working back from your official NHS 12-week dating scan allows you to establish the exact 5-day window during which fertilizing intercourse occurred.
In the UK, prenatal care guidelines emphasize that ovulation typically occurs 14 days before your next period, making cycle regularity a key consideration.
Worked example: NHS scan correlation
An NHS 12-week scan dates your pregnancy with an EDD of 20 May.
Subtracting 266 days places conception around 27 August, with intercourse having occurred between 24 and 28 August.
UK conception inputs
Known Date
Enter your NHS estimated due date or LMP.
CALCULATOR QUESTIONS
UK conception date & fertile intercourse calculator questions
Does knowing conception date change my NHS due date?
No. The NHS will always maintain the due date established by your 12-week dating scan as the clinical standard for all maternity care and scheduled induction planning.
How long does an egg survive after ovulation?
An egg survives for approximately 12 to 24 hours after release from the ovary, whereas sperm can survive up to 5 days in cervical mucus.