What is the proper way of calculating when they come? I'm used to just going by "the feeling." like when I start to get moody and little signs, then I know it's coming. But this coming month I have a camping trip, and I want to be sure to schedule it when I'm not on my period. Is it 28 days after you last period?? and if it is, is it 28 days from the day you first got your period, or 28 days from when it ended?? :?