Period Calculator
Predict your next period date from your last period and cycle length.
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How Period Prediction Works
Your next period is estimated by adding your average cycle length to the first day of your last period. Repeating this projects several cycles ahead.
Next period = last period start + cycle lengthCycle length is measured from the first day of one period to the first day of the next, not from the end of bleeding.
A typical cycle ranges from 21 to 35 days. The more regular your cycles, the more reliable the prediction.
Worked Example
If your last period started on 1 March with a 28-day cycle, your next period is predicted around 29 March, then 26 April, then 24 May.
What Affects Cycle Length
Stress, significant weight change, intense exercise, travel, illness, and hormonal conditions can all shift cycle timing. Many people experience some natural variation from month to month, which is why predictions are estimates rather than exact dates.
Frequently Asked Questions
How is cycle length measured?
Count from the first day of bleeding in one period to the first day of bleeding in the next. That total number of days is your cycle length.
What counts as a regular cycle?
Cycles between 21 and 35 days that vary by only a few days each month are generally considered regular. Larger swings are common but worth discussing with a provider if persistent.
Why might my period be late?
Stress, illness, weight changes, travel, hormonal shifts, and pregnancy are common causes. A consistently irregular or absent cycle is worth medical review.
Note: Predictions are estimates for informational purposes only and are not medical advice. Consult a qualified healthcare provider for concerns about your cycle.