Measure how long your average cycle is, i.e., the time between one period beginning and the next one beginning. If you are unsure, use the average value of 28 days.
Note how long your average period duration is. If you do not know this value, use the average of 6 days.
Add the length of your cycle to the date your last period began. This is the day your next period should begin.
Add the length of your period to the date your next period will begin. This is when your next period should end.
Check your calculations with the Omni Period Calculator.
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