Enter your last period and cycle length to forecast your next three predicted cycles, ovulation, and fertile window.
Estimates only.
Rather than showing a single next date, this calculator projects three cycles forward using the same cycle length applied each time, so you can see how the forecast compounds and where it is likely to drift.
| Cycle | Predicted start date |
|---|---|
| Next | -- |
| Following | -- |
| Third out | -- |
Cycle length is the gap from the first day of one period to the first day of the next, and it is the only number this calculator uses to project forward. Period length, how many days bleeding lasts, is recorded here for your own tracking but does not shift any of the predicted dates, since it does not affect when the next cycle begins. This calculator uses the standard model: next period equals your last period date plus cycle length, repeated for each additional cycle. Estimated ovulation falls about 14 days before the next predicted period, and the fertile window spans roughly six days ending on that ovulation day.
Cycle lengths vary naturally from month to month, and travel, illness, stress, and sleep disruption can all shift ovulation and, with it, the start of the next period. A period arriving a few days early or late compared with this forecast is common and not on its own a cause for concern. If a period is significantly late, especially alongside other symptoms, a home pregnancy test and a conversation with your doctor or midwife are the next reasonable steps. Persistent irregularity over several cycles is also worth discussing with a provider, since an ultrasound or hormone panel can assess cycle and ovulation patterns more directly than date forecasting.
It's recorded for your own reference and future tracking. The predicted start dates depend only on cycle length, since that determines when the next cycle begins, not how many days bleeding lasts.
The next one or two cycles are usually the most reliable. Forecasts further out assume your cycle length stays constant, which is less likely the further ahead you look.
There is no single cutoff, but many providers consider a period more than about 5 days past its predicted date worth noting, especially if it is unusual for you.
Yes. Cycle length is sensitive to stress, illness, travel, and sleep disruption, all of which can shift ovulation and, with it, your next period.