Period Calculator

Estimate your next several period dates and most probable ovulation windows from your last period and cycle length.

How future periods are estimated

Each future period is projected by repeatedly adding your average cycle length to the start date of your last period. Ovulation for each cycle is estimated the same way as our Ovulation Calculator: about 14 days before that cycle's next period starts.

Why these are estimates, not certainties

Cycle length naturally varies from month to month for most people — stress, illness, travel, and many other factors can shift timing. The further out a projected cycle is, the more that natural variation can accumulate, so treat later cycles in the table as rougher estimates than the very next one.

This calculator is for general tracking and planning, not medical or contraceptive use. If your cycles are irregular or you have concerns about your cycle, consult a healthcare provider.

Common questions

What if my cycle length varies a lot month to month?

Use your typical or average cycle length for the best estimate, and treat the projections as a general guide rather than an exact schedule — irregular cycles make advance predictions less reliable.

How is this different from the Ovulation Calculator?

This tool also projects your period date ranges across 6 cycles, while our Ovulation Calculator adds extra fertility details like the intercourse window and an estimated due date if that cycle resulted in pregnancy.

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