When do I ovulate on a 39-day cycle?
Ovulation usually happens about 14 days before the next period starts. On a 39-day cycle, the next period starts on day 40, so ovulation is most likely around day 25 (counting the first day of your period as day 1). A 39-day cycle is a long cycle; cycles from about 21 to 35 days are common in adults.
Your fertile window on a 39-day cycle
Sperm can live for up to five days and an egg for about a day, so the fertile window is the five days before ovulation plus ovulation day: cycle days 20 to 25. The best days to try are days 23 to 25.
| Cycle day | Fertility |
|---|---|
| Day 18 | Low chance |
| Day 19 | Low chance |
| Day 20 | Fertile |
| Day 21 | Fertile |
| Day 22 | Fertile |
| Day 23 | Most fertile |
| Day 24 | Most fertile |
| Day 25 | Ovulation (most fertile) |
| Day 26 | Fertility falls quickly |
| Day 27 | Fertility falls quickly |
| Day 28 | Fertility falls quickly |
Does my period length matter?
No — whether your period lasts 3, 5 or 7 days, ovulation on a 39-day cycle is still around day 25. With a 5-day period, that is about 20 days after your period ends.
How sure is this?
The 14-day rule is an average: the second half of the cycle usually lasts 12 to 16 days, so ovulation on a 39-day cycle could be anywhere from about day 23 to day 27. Ovulation tests, which detect the LH surge, or temperature charting can confirm your own pattern. If your cycles vary a lot, enter your average cycle in the Ovulation Date Calculator and treat the dates as approximate.
Other cycle lengths
34-day cycle · 35-day cycle · 36-day cycle · 37-day cycle · 38-day cycle · 40-day cycle