Period Calculator
Calculate your next period date and cycle info from your last menstrual period.
Inputs
Results
Next Period
Wednesday, Sep 2, 2026
Ovulation
Wednesday, Aug 19, 2026
Fertile Window
Friday, Aug 14, 2026 – Thursday, Aug 20, 2026
- 1Enter the first day of your last period (LMP) — the day bleeding started, not spotting.
- 2Set your average cycle length (21–35 days is typical; default is 28).
- 3Review next period date, estimated ovulation, and the fertile window in the results.
- Log your actual period start dates in a app or calendar to refine your personal average cycle length over time.
About the Period Calculator
Predicts your next period date, ovulation day, and fertile window from your last menstrual period (LMP) and average cycle length.
Use when planning travel, workouts, or appointments around your cycle, or when tracking regularity between doctor visits.
Next period = LMP + cycle length. Ovulation ≈ LMP + (cycle length − 14 days). Fertile window ≈ 5 days before through 1 day after ovulation.
LMP January 1 with a 28-day cycle → next period around January 29, ovulation around January 15, fertile window roughly January 10–16.
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