Ovulation in a 39-day cycle: day 25
In a 39-day cycle, ovulation around day 25 is nearly two weeks later than the textbook day 14.
A positive pregnancy test can take longer to appear; test from day 40, and if you conceive, expect an early scan to give a later due date than a last-period calculation.
Ovulation is usually about 14 days before the next period, so in a 39-day cycle it falls on day 25 — 11 days later than in a 28-day cycle. A 39-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 39-day cycle, phase by phase
| Phase | Cycle days |
|---|---|
| Period (typical) | Days 1–5 |
| Follicular phase | Days 1–24 (24 days) |
| Fertile window | Days 20–26, best on days 23–25 |
| Ovulation | Day 25 |
| Luteal phase | Days 26–39 (14 days) |
Start LH ovulation tests around day 22; a positive result on day 23 or 24 points to ovulation on day 25.
If your cycle is sometimes 37 or 41 days
Few cycles are identical every month. If yours ranges between 37 and 41 days, ovulation could fall anywhere from day 23 to day 27, which widens your possible fertile days to days 18 to 28. Base the start of ovulation testing on your shortest recent cycle (day 20), and expect your period between day 38 and day 42.
| Cycle length | Ovulation | Fertile window |
|---|---|---|
| 37 days | Day 23 | Days 18–24 |
| 38 days | Day 24 | Days 19–25 |
| 39 days | Day 25 | Days 20–26 |
| 40 days | Day 26 | Days 21–27 |
Example: a 39-day cycle starting today
| Period starts (day 1) | |
|---|---|
| Start ovulation tests (day 22) | |
| Fertile window (days 20–26) | – |
| Estimated ovulation (day 25) | |
| Next period / test day (day 40) |
Test for pregnancy from day 40 — see the Pregnancy Test Calculator for exact dates.