Period Calculator
Enter the first day of your last period and your average cycle length to predict your next three period start dates. A simple, private period estimator — no tracking, no accounts.
How This Period Calculator Works
This calculator uses a simple forward projection: it adds your average cycle length to the first day of your last menstrual period to estimate when your next period will start, repeating for up to three future cycles. For example, with a 28-day cycle starting January 1st, your next period would be predicted around January 29th, followed by February 26th and March 26th.
Limitations of Period Prediction
Cycle length naturally varies from person to person and even from month to month. Stress, travel, illness, weight changes, intense exercise, and hormonal fluctuations can all affect cycle timing. This calculator provides an estimated date only and should not be relied upon for critical planning or as a form of birth control.
If your cycles are consistently shorter than 21 days, longer than 35 days, or vary by more than 7–9 days from month to month, consider speaking with a healthcare provider. Irregular cycles can sometimes indicate underlying conditions such as polycystic ovary syndrome (PCOS), thyroid disorders, or other hormonal imbalances.
Beyond Period Tracking
While this is a simple period predictor (not a full tracking app), understanding your cycle can help you recognize patterns in your body, plan ahead for events and travel, and identify when something may be worth discussing with your doctor. For daily cycle tracking with symptom logging, dedicated apps are available — but this tool remains a quick, private alternative that stores none of your data.