When do I ovulate on a 40-day cycle?
Ovulation usually happens about 14 days before the next period starts. On a 40-day cycle, the next period starts on day 41, so ovulation is most likely around day 26 (counting the first day of your period as day 1). A 40-day cycle is a long cycle; cycles from about 21 to 35 days are common in adults.
Your fertile window on a 40-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 21 to 26. The best days to try are days 24 to 26.
| Cycle day | Fertility |
|---|---|
| Day 19 | Low chance |
| Day 20 | Low chance |
| Day 21 | Fertile |
| Day 22 | Fertile |
| Day 23 | Fertile |
| Day 24 | Most fertile |
| Day 25 | Most fertile |
| Day 26 | Ovulation (most fertile) |
| Day 27 | Fertility falls quickly |
| Day 28 | Fertility falls quickly |
| Day 29 | Fertility falls quickly |
Does my period length matter?
No — whether your period lasts 3, 5 or 7 days, ovulation on a 40-day cycle is still around day 26. With a 5-day period, that is about 21 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 40-day cycle could be anywhere from about day 24 to day 28. 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 · 39-day cycle