NHS menstrual health standards and GP care
Under NHS clinical guidance, a normal period lasts between 2 and 7 days, with an entire cycle duration of 21 to 35 days.
The NHS advises women to see a GP if periods suddenly become irregular, if bleeding occurs between periods or after sex, or if heavy menstrual bleeding (menorrhagia) disrupts daily activities.
Cycle tracking helps your GP determine whether irregular bleeding reflects hormonal conditions such as Polycystic Ovary Syndrome (PCOS), thyroid dysfunction, or perimenopause.
Worked example: NHS cycle tracking
A patient logs an LMP of 15 September with a 28-day cycle and 5 days of bleeding.
Next periods are projected for 13 October, 10 November, and 8 December, with mid-cycle ovulation around 29 September.
UK period inputs
Start Date
Date bleeding began in your last cycle.
CALCULATOR QUESTIONS
NHS menstrual cycle & period tracker questions
What does the NHS classify as heavy periods?
Periods are classified as heavy if you need to change your pad or tampon every 1 to 2 hours, pass blood clots larger than a 10p coin, or bleed through to your clothes or bedding.
Can hormonal contraception alter my cycle predictions?
Yes. Combined hormonal pills, patches, and vaginal rings produce withdrawal bleeds rather than true menstrual periods, whereas the progestogen-only pill or hormonal coil (IUS) may stop bleeding entirely.