Period Calculator
Use this free period calculator to predict when your next period is due. Enter the first day of your last period and your average cycle length, and we will estimate your next three periods.
Knowing your period dates is the first step in cycle syncing: once you know where you are in your cycle, you can plan your food, workouts, and skincare around your hormones instead of guessing.
Sync your whole cycle, automatically
PhaseBloom builds your meals, workouts, and skincare around your exact cycle phase, day by day.
How it works
Your cycle is counted from the first day of one period to the first day of the next. The average is 28 days, but anywhere from 21 to 35 days is common and healthy.
This calculator adds your cycle length to your last period date to project future periods. The more accurately you know your average cycle length, the more accurate the prediction.
Frequently asked questions
How accurate is a period calculator?
It is an estimate based on your average cycle length. Cycles naturally vary by a few days, so use it as a guide rather than a guarantee. Tracking a few cycles makes it more accurate.
What is a normal cycle length?
Most cycles run 21 to 35 days. What matters more than the exact number is that yours is fairly consistent for you.