This is totally normal. You might skip a month or have a period earlier or later than you thought it would come. The length of the period (bleeding) can also vary. This is a normal part of growing into an adult. Since each girl’s cycle is different, periods can come anywhere from every 21 days to every 28, to even every 34 days. They can also come anywhere in there or earlier. Eventually, a girl’s cycle will stabilize and it’ll be easier to know when to expect a period.