Question: How long is a typical menstruation cycle?
The menstruation cycle, the monthly cycle fertile women and girls experience, typically lasts 28 days. That means that many menstruating women and girls get their period every 28 days. But a normal menstruation cycle can vary anywhere between 21 and 35 days between periods. It's not unusual for tween and teen girls to have irregular periods -- in fact it may take months before a girl can accurately track her period
Because your tween may not always know when to expect her period, she should be aware of premenstrual symptoms, and always make sure that she carries menstrual pads or tampons with her, in case her period presents itself unexpectedly.
The more your tween daughter understands about her menstruation cycle, the easier puberty will be for both of you.