Ovulation calculator
Ovulation is placed by counting the luteal phase back from your next expected period. The fertile window runs from five days before ovulation to one day after.
- Fertile window
- 2026-10-14 → 2026-10-20
- Next period expected
- November 2, 2026
- Due date if conception occurs
- July 12, 2027
- Cycle day today
- 17
- Days to ovulation
- -2 days
| Cycle | Period | Ovulation | Fertile window |
|---|---|---|---|
| 1 | November 2, 2026 → November 6, 2026 | November 16, 2026 | November 11, 2026 → November 17, 2026 |
| 2 | November 30, 2026 → December 4, 2026 | December 14, 2026 | December 9, 2026 → December 15, 2026 |
| 3 | December 28, 2026 → January 1, 2027 | January 11, 2027 | January 6, 2027 → January 12, 2027 |
| 4 | January 25, 2027 → January 29, 2027 | February 8, 2027 | February 3, 2027 → February 9, 2027 |
| 5 | February 22, 2027 → February 26, 2027 | March 8, 2027 | March 3, 2027 → March 9, 2027 |
| 6 | March 22, 2027 → March 26, 2027 | April 5, 2027 | March 31, 2027 → April 6, 2027 |
Estimates for a regular cycle. They vary from cycle to cycle, are not a contraceptive method, and do not replace medical advice.
The formula
Ovulation = first day of last period + cycle length − luteal phase. Fertile window = ovulation − 5 days to ovulation + 1 day. Due date uses Naegele's rule, 280 days from the last period, adjusted for cycle lengths other than 28 days.
Worked example
With a 28-day cycle and a 14-day luteal phase, ovulation falls on day 14, the fertile window runs from day 9 to day 15, and a pregnancy would be due 280 days after the period started.
How to use it
- 1Count day one as the first day of real bleeding, not spotting.
- 2The luteal phase is the steadier half of the cycle; 14 days is typical and 12 to 16 is normal.
- 3If your cycles vary by more than a few days, read the window as wide rather than exact.
Questions people ask
Can I use this to avoid pregnancy?
No. Cycles shift, sperm survive several days, and ovulation can move without warning. For contraception, use a method designed for it and talk to a clinician.
Why does my app say a different day?
Most apps learn from your logged cycles and adjust; this uses the numbers you enter. Ovulation tests and basal temperature confirm what any calendar can only estimate.
Last reviewed: 2026-10-20