Ovulation Calculator with Period and Fertile Window

It estimates the next period date, ovulation date, fertile window, current cycle day, cycle phase and a multi-cycle period calendar.

The calculator subtracts the selected luteal-phase length from the predicted first day of the next period. The default luteal phase is 14 days.

Ovulation commonly occurs about 10 to 16 days before the next period, so the cycle day depends on total cycle length and individual variation.

It shows an estimated six-to-seven-day planning window from five days before ovulation through one day after. Actual fertility can vary.

No. Calendar calculations cannot confirm ovulation. Hormonal testing, cervical-mucus observations, basal temperature patterns and clinical assessment can provide additional information.

No. The estimates are not reliable enough to prevent pregnancy and should not replace an effective contraceptive method.

No. It cannot detect pregnancy. Use an appropriate pregnancy test and consult a qualified healthcare professional when needed.

Cycle day 1 is the first day of menstrual bleeding, not the final day of the previous period.

Cycle length is counted from the first day of one period to the first day of the next period.

Average-cycle mode accepts 15 to 90 days. Results outside the common adult range are shown with a caution because calendar prediction may be unreliable.

You can enter a period length from 1 to 14 days. The value is used only to shade the predicted bleeding dates in the calendar.

You can enter 8 to 20 days. Use a clinician-confirmed or personally tracked value when available; otherwise 14 days is a common calendar assumption.

Enter two to twelve period start dates. The calculator measures the intervals, then uses the rounded average for central predictions and the shortest and longest intervals for an uncertainty range.

Either order works. The calculator sorts valid unique dates before calculating intervals.

Duplicate dates are ignored. At least two unique period start dates are required for history mode.

It is the difference between the shortest and longest recorded cycle intervals. It describes the entered dates only and is not a diagnosis.

In history mode, the earliest estimate uses the shortest recorded cycle and the latest estimate uses the longest recorded cycle.

Ovulation and cycle timing can shift because of normal variation, stress, illness, travel, hormonal changes, postpartum changes, perimenopause and other factors.

Yes. Hormonal contraception can change or suppress ovulation and bleeding patterns, so a simple calendar estimate may not represent natural ovulation.

You can use history mode to display a wider estimate, but predictions are less dependable when cycle intervals vary substantially.

Conditions that affect ovulation, including PCOS, can make calendar predictions unreliable. Discuss irregular or absent periods with a qualified clinician.

Yes. Ovulation and bleeding may be unpredictable after childbirth and while breastfeeding, so the calculated dates may not be dependable.

It is an educational calendar label based on predicted period and fertile-window dates. It does not confirm hormone levels or ovulation.

It is the number of whole calendar days between the selected as-of date and the next predicted period start.

Yes. Change the as-of date to view the estimated cycle day and nearest predicted events for a past or future date.

The table can show from 3 to 12 projected cycles.

Calculations use whole UTC calendar days, so daylight-saving changes do not add or remove a day and leap dates are handled correctly.

Yes. Download a text report or a CSV table. Generated filenames begin with correctioncopy.com_.

Yes. Use Print to open the browser print dialog, where supported browsers can also save the page as a PDF.

No page-specific request uploads the entered cycle dates. Calculations and exports are created in the browser, and Reset clears the active workspace.

No account or installation is required. JavaScript must be enabled for calculation and export functions.

Seek professional advice for concerns such as very heavy bleeding, severe pain, pregnancy concerns, periods that stop unexpectedly, or persistent cycle changes.