"Regular" periods means that the time between periods is pretty much the same from month to month. Women can have their periods every 21 to 35 days, 28 days is the average. But when you first start menstruating, you may experience irregular periods . You could have one period and then wait six months for the next one! This isn’t unusual. Until your body adjusts, the time between your periods may be unpredictable. But after that, it should regulate itself. If not, see your doctor.