Estimate a possible ovulation date and fertile window using the first day of a recent period and your average cycle length. The calendar model places ovulation about 14 days before the estimated next period, then displays five days before through one day after that estimate. Ovulation can occur earlier or later, even in regular cycles. This tool cannot confirm ovulation, diagnose fertility, or serve as contraception; seek a clinician's advice for reproductive-health decisions.
Enter the first day of a recent period and average cycle length.
Review the estimated ovulation date and surrounding fertile-window dates.
Treat the result as uncertain calendar information, not contraception or diagnosis.
Estimated next period: Last period start + average cycle length
Estimated ovulation: Estimated next period − 14 days
Calendar fertile window: Estimated ovulation − 5 days through + 1 day
Can this confirm ovulation?
No. It uses average cycle length only. Ovulation tests or clinical evaluation may provide different information.
Can I use the fertile window to avoid pregnancy?
No. Calendar estimates are not reliable contraception. Ask a qualified health professional about effective options.