The time from the first sign of blood to the last is usually in the 3-to-5-day range. It’s common for cycles to be a little irregular for a few years after your first period. This means your periods may not always come at the same time every cycle, and they may be a bit different from one month to the next. Don’t worry, as you progress through adolescence, your cycles will become more regular and start to reflect adult cycle ranges, but they may still be a bit variable.