Hi KarineT
As CLKD says, menopause is the last ever period, but can only ever be determined in retrospect and never, if you start HRT while still peri-menopausal and continue taking it through the transition and beyond.
The question is then, at what point can you say you have reached menopause? How long do you wait? The age that women reach this point is obviously variable, as is the pattern of cycles leading up to the last period.
Just to add that for contraceptive purposes, exactly as Taz says, the rule is you wait two years if under 50 and one year if over 50 for the reasons she says.
However for the purposes of post-menopausal bleeding and the trigger for investigation, it is set at 12 months for everyone (it used to be 2 years for under 50 but was changed).This is to ensure that any potential cases of cancer (or womb thickening that could lead to cancer) are not missed in women under 50.
That's it really. These are arbitrary dates set for specific reasons and to take into account what might happen. Many women will experience a natural period after the 12 months time has elapsed but all will be investigated if bleeding is reported.
The definitions are explained here:
https://www.menopausematters.co.uk/menopause.phpHope this helps
Hurdity x