Period Calculator
Know what's coming, before it comes
Enter the first day of your last period and your average cycle length to get a quick estimate of your next period and fertile window.
Everything you enter here stays on your device — nothing is saved or sent anywhere. Refresh the page and it's gone.
21 days40 days
Not sure? 28 days is the average — you can always recalculate once you know your own rhythm better.
Enter the first day of your last period to see your estimated next cycle.
These are estimates based on average cycle patterns, not a medical prediction — real cycles vary, especially in the first few years after periods start. If your cycle is very irregular, unusually painful, or missing for months, that's worth mentioning to a health professional.
You don't have to figure this out alone.
Whether it's a quick question or something you've been carrying for a while — we're a message away, and it stays between us.