Ovulation in a 27-day cycle: day 13
At 27 days your cycle is almost exactly average, with ovulation around day 13.
Small month-to-month changes of a day or two are normal at this length, so treat days 11 to 14 as your likely ovulation range.
Ovulation is usually about 14 days before the next period, so in a 27-day cycle it falls on day 13 — 1 day earlier than in a 28-day cycle. A 27-day cycle is within the usual adult range of about 21–35 days.
Your 27-day cycle, phase by phase
| Phase | Cycle days |
|---|---|
| Period (typical) | Days 1–5 |
| Follicular phase | Days 1–12 (12 days) |
| Fertile window | Days 8–14, best on days 11–13 |
| Ovulation | Day 13 |
| Luteal phase | Days 14–27 (14 days) |
Start LH ovulation tests around day 10; a positive result on day 11 or 12 points to ovulation on day 13.
If your cycle is sometimes 25 or 29 days
Few cycles are identical every month. If yours ranges between 25 and 29 days, ovulation could fall anywhere from day 11 to day 15, which widens your possible fertile days to days 6 to 16. Base the start of ovulation testing on your shortest recent cycle (day 8), and expect your period between day 26 and day 30.
| Cycle length | Ovulation | Fertile window |
|---|---|---|
| 25 days | Day 11 | Days 6–12 |
| 26 days | Day 12 | Days 7–13 |
| 27 days | Day 13 | Days 8–14 |
| 28 days | Day 14 | Days 9–15 |
| 29 days | Day 15 | Days 10–16 |
Example: a 27-day cycle starting today
| Period starts (day 1) | |
|---|---|
| Start ovulation tests (day 10) | |
| Fertile window (days 8–14) | – |
| Estimated ovulation (day 13) | |
| Next period / test day (day 28) |
Test for pregnancy from day 28 — see the Pregnancy Test Calculator for exact dates.