Most people under 40 who have regular sex without contraception conceive within a year. NICE guidance suggests talking to a doctor if it has not happened after a year of trying.
If you are using donor sperm, are trying on your own or are in a same sex relationship, the timing works differently. A doctor or fertility clinic can tell you when to come.
When to go sooner
NICE suggests going sooner if you are 36 or older, and many doctors and other guidelines suggest going after 6 months of trying from the age of 35.
It is also worth going sooner if periods are very irregular or absent, if you know of a condition such as PCOS or endometriosis, if you have had pelvic infections, surgery or cancer treatment, or if your partner has a known health issue that may affect fertility.
Any time
You can always talk to your doctor or gynaecologist when something worries you, whatever the timing. For severe pain in the belly, especially if you might be pregnant, heavy bleeding, fainting or feeling very unwell, seek care straight away or call 112.