Enter First day of last period, Average cycle length (days) and Luteal phase length (days) and the remaining scenario settings to review ovulation date with this tool. The estimated ovulation date and window follow assumptions about cycle timing.
The date estimate is calculated from the entered cycle, last menstrual period, conception date or gestational reference using standard calendar intervals.The calculation links First day of last period, Average cycle length (days) and Luteal phase length (days) to ovulation date. The estimated ovulation date and window follow assumptions about cycle timing. Calendar dates cannot confirm that ovulation occurred.
Enter First day of last period, Average cycle length (days) and Luteal phase length (days) and the remaining scenario settings to review ovulation date with this tool. The estimated ovulation date and window follow assumptions about cycle timing.
Map an illustrative cycle calendar from the entered last-period date and cycle-length assumptions. Use the date range to understand the calendar method.
The estimated ovulation date and window follow assumptions about cycle timing. Calendar dates cannot confirm that ovulation occurred.
Prepare First day of last period, Average cycle length (days), Luteal phase length (days) and Cycle regularity. Enter the first day of the last period and the usual complete cycle length, rather than the number of bleeding days.
The estimated ovulation date and window follow assumptions about cycle timing. Calendar dates cannot confirm that ovulation occurred. Cycle variation and individual fertility factors can shift timing. This tool must not be used as a reliable contraception method or a fertility diagnosis.
Use the full settings in the worked-example table. They produce Ovulation Date: January 15, 2026. Compare the method and units as well as the displayed number.
The displayed relationship is The date estimate is calculated from the entered cycle, last menstrual period, conception date or gestational reference using standard calendar intervals. Enter the first day of the last period and the usual complete cycle length, rather than the number of bleeding days.
Cycle variation and individual fertility factors can shift timing. This tool must not be used as a reliable contraception method or a fertility diagnosis. For personal care, discuss the measurements and method with a qualified clinician.
Worked ovulation calculator example. Set First day of last period = 2026-01-01; Average cycle length (days) = 28; Luteal phase length (days) = 14; Cycle regularity = Regular. The corresponding output is Ovulation Date: January 15, 2026. The estimated ovulation date and window follow assumptions about cycle timing.
Map an illustrative cycle calendar from the entered last-period date and cycle-length assumptions. Use the date range to understand the calendar method.
Enter the first day of the last period and the usual complete cycle length, rather than the number of bleeding days.
| Field | Example value | Entry check |
|---|---|---|
| First day of last period | 2026-01-01 | Use the period unit in the field label; months and years are not interchangeable. |
| Average cycle length (days) | 28 | Use the stated unit and the measurement required by this model. |
| Luteal phase length (days) | 14 | Use the stated unit and the measurement required by this model. |
| Cycle regularity | Regular | Use the stated unit and the measurement required by this model. |
Relationship used for this example: The date estimate is calculated from the entered cycle, last menstrual period, conception date or gestational reference using standard calendar intervals.
The estimated ovulation date and window follow assumptions about cycle timing. Calendar dates cannot confirm that ovulation occurred.
| Output | Displayed result |
|---|---|
| Ovulation Date | January 15, 2026 |
With these settings, ovulation date is January 15, 2026. Use the same units and calculation mode when reproducing this example.
The estimated ovulation date and window follow assumptions about cycle timing. Calendar dates cannot confirm that ovulation occurred. Cycle variation and individual fertility factors can shift timing. This tool must not be used as a reliable contraception method or a fertility diagnosis.
Replace the illustrative first day of last period value (2026-01-01) with your own value, then complete the other inputs for the same scenario. Enter the first day of the last period and the usual complete cycle length, rather than the number of bleeding days.