NHS natural conception and referral criteria
NHS guidelines advise that 84% of couples will conceive naturally within a year if they have regular unprotected sex (every 2 to 3 days throughout the cycle). Trying to time intercourse to the exact hour of ovulation can cause unnecessary stress.
Under NICE guideline CG156, women under 36 who have not conceived after 12 months of regular unprotected intercourse should be offered an initial fertility assessment by their NHS GP.
Women aged 36 and older, or those with known risk factors such as irregular periods (oligomenorrhea), history of pelvic inflammatory disease (PID), or endometriosis, should consult their GP after 6 months.
Worked example: NHS fertility timeline
For a period starting on 1 October with regular 28-day cycles, ovulation occurs on 15 October.
Having unprotected intercourse on 13, 14, and 15 October maximizes natural conception probability under NHS recommendations.
UK ovulation inputs
Period Start Date
First day of menstrual bleeding.
CALCULATOR QUESTIONS
NHS fertile window & ovulation calculator questions
When does the NHS consider a cycle irregular?
The NHS defines normal menstrual cycles as lasting between 21 and 35 days. Cycles varying by more than 7 to 9 days or lasting outside this range warrant GP evaluation.
Do ovulation predictor kits (OPKs) work for everyone?
OPKs detect the LH surge that triggers ovulation 24 to 36 hours later. They are highly effective for regular cycles, but may be unreliable for individuals with polycystic ovary syndrome (PCOS) due to chronically elevated baseline LH levels.