Don’t freak out—or, at least don’t show it. “Staying neutral and calm is important,” Louise Greenspan, MD, co-author of The New Puberty: How to Navigate Early Development in Today’s Girls, tells Yahoo Parenting. Although the average age for girls to get their first period is 12, there is a range. “Under age 10 might also be normal,” says Greenspan, “but [if that happens], touch base with your pediatrician.” A good rule of thumb: A girl can expect her first period two to three years after developing breasts or pubic hair. So, if these puberty-related changes were spotted at age 8, for example, it’s likely that a period would occur around age 10. Whenever it happens, prep your daughter for this new stage by having a frank conversation about what she can expect, —hormonal changes, cramping, bloating, hygiene — and advise her to always carry a stash of tampons or napkins in her backpack so she’s prepared.