Period & cycle tools
Estimate when your next period may start and how your current cycle is progressing. These tools use simple cycle math and the dates you enter — they do not diagnose irregular bleeding or other conditions.
Period calculators
Start here if you want a next-period estimate or a clearer view of your cycle timing.
What period predictions can tell you
A period calculator projects forward using the first day of your last period and your average cycle length. If you have tracked several cycles, the average is usually more useful than a single cycle. The result is a planning estimate: it can help you prepare for an expected period or notice when your cycle differs from your usual pattern.
The same cycle math can estimate ovulation, typically placed about 14 days before the next period. That estimate is less reliable than the next-period estimate, especially if your cycles are irregular.
What can shift a cycle
- Stress, poor sleep, illness, and travel
- Significant weight change or changes in exercise
- Starting, stopping, or changing hormonal medication
- Pregnancy, breastfeeding, perimenopause, and other hormonal changes
When to talk to a healthcare professional
Seek advice if your periods are very irregular, unusually heavy, painful enough to disrupt daily life, or if you bleed between periods or after sex. These symptoms can have many causes, and a calculator cannot assess them.
Related tools
If you are trying to conceive or want to understand the days around ovulation, see the ovulation calculator and the fertile window calculator. If you are pregnant, use the due date calculator. For the full method, read how to calculate your next period.