Period Due Date Calculator
Enter your last period date and cycle length to find out exactly when your next period is due — and how many days away it is.
Typically 21–35 days
How this calculator works
Your next period is estimated by adding your cycle length to the first day of your last period. If your cycle is 28 days and your last period started on the 1st, your next period is due on the 29th. The ovulation window shown is based on the standard assumption that ovulation occurs 14 days before your next period.
Why tracking matters more than calculating
Cycle length varies from month to month — sometimes by 3–5 days, and more if you have PCOS or are approaching perimenopause. A calculator gives you a one-time estimate based on a single cycle. Dawn Phase tracks your actual patterns across multiple cycles and improves its predictions the more you log.
Note: These are estimates only and should not be used for contraception or medical decision-making. Consult a healthcare provider with any concerns.
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