Free health calculator
Period cycle calculator
Enter your last period start date and cycle pattern to estimate the next period, fertile window, ovulation day, and where you are today.
Track your cycle on iPhone
Cyca gives you a more complete private period and cycle tracking workflow.
Period cycle calculator FAQ
Is this period cycle calculator medical advice?
No. It is an educational estimator based on average cycle math and should not replace medical advice.
Does my cycle data leave the browser?
No. Your dates are calculated locally in your browser and are not uploaded.
How accurate is the fertile window?
It is an estimate. Real ovulation can shift with stress, sleep, illness, travel, and individual variation.