Ovulation in a 40-day cycle: day 26
A 40-day cycle is well beyond the usual range. If ovulation happens, it is probably around day 26, but cycles this long are often irregular.
It is worth asking a healthcare professional about cycles this long, especially if they are new, you are trying to conceive, or you have other symptoms.
Ovulation is usually about 14 days before the next period, so in a 40-day cycle it falls on day 26 — 12 days later than in a 28-day cycle. A 40-day cycle is longer than the usual adult range of about 21–35 days. Longer cycles usually mean ovulation happens later — and sometimes less regularly — so it is worth talking to a doctor or nurse if your cycles are regularly this long, especially if you are trying to conceive.
Your 40-day cycle, phase by phase
| Phase | Cycle days |
|---|---|
| Period (typical) | Days 1–5 |
| Follicular phase | Days 1–25 (25 days) |
| Fertile window | Days 21–27, best on days 24–26 |
| Ovulation | Day 26 |
| Luteal phase | Days 27–40 (14 days) |
Start LH ovulation tests around day 23; a positive result on day 24 or 25 points to ovulation on day 26.
If your cycle is sometimes 38 or 42 days
Few cycles are identical every month. If yours ranges between 38 and 42 days, ovulation could fall anywhere from day 24 to day 28, which widens your possible fertile days to days 19 to 29. Base the start of ovulation testing on your shortest recent cycle (day 21), and expect your period between day 39 and day 43.
| Cycle length | Ovulation | Fertile window |
|---|---|---|
| 38 days | Day 24 | Days 19–25 |
| 39 days | Day 25 | Days 20–26 |
| 40 days | Day 26 | Days 21–27 |
Example: a 40-day cycle starting today
| Period starts (day 1) | |
|---|---|
| Start ovulation tests (day 23) | |
| Fertile window (days 21–27) | – |
| Estimated ovulation (day 26) | |
| Next period / test day (day 41) |
Test for pregnancy from day 41 — see the Pregnancy Test Calculator for exact dates.