When you’re trying to conceive, knowing when you ovulate is the single most useful thing you can learn — because it tells you your most fertile days. The good news: your body usually gives several signals. Here’s what to look for.
What is the “fertile window”?
You can only get pregnant around ovulation, when your ovary releases an egg. That egg lives for about 12–24 hours. But sperm can survive in the body for up to five days, so your fertile window is roughly six days long: the five days before ovulation plus ovulation day itself. The two days right before you ovulate are the most fertile of all.
- Period · Days 1–5 Your period — the start of a new cycle.
- Pre-ovulation · Days 6–11 An egg matures and mucus starts to change.
- Fertile window · Days 12–16 Ovulation around day 14 — your most fertile days.
- After ovulation · Days 17–28 The luteal phase, until your next period.
That’s why the goal isn’t to catch the exact moment of ovulation — it’s to recognise it’s coming, so you can time things in the days beforehand. In a textbook 28-day cycle ovulation falls around day 14, but plenty of healthy cycles ovulate earlier or later, which is why the body signs below beat the calendar.
The most reliable signs of ovulation
1. Egg-white cervical mucus
This is the most useful day-to-day sign. As ovulation approaches, cervical mucus becomes clear, slippery and stretchy — like raw egg white. This fertile-quality mucus helps sperm travel, and its peak usually lines up with your most fertile days. After ovulation it typically turns cloudy, sticky or dries up.
2. A positive ovulation test (the LH surge)
Ovulation predictor kits (OPKs) detect a surge in luteinising hormone (LH) that happens about 24–36 hours before ovulation. A positive test is one of the best ways to know ovulation is about to happen — a green light to try over the next day or two. For the clearest result, test at the same time each afternoon or early evening (not first thing in the morning), when LH is most likely to show up in your urine.
3. A rise in basal body temperature (BBT)
After ovulation, progesterone causes a small, sustained rise in your resting body temperature (about 0.3–0.5°C). Charting your BBT each morning confirms that ovulation has happened — useful for spotting your pattern over a few cycles, though it doesn’t predict ahead.
4. Other, subtler signs
Some people also notice:
- Ovulation pain — a one-sided twinge or ache (mittelschmerz).
- A softer, higher, more open cervix.
- A higher sex drive around the fertile window.
- Light spotting or mild breast tenderness.
These vary a lot from person to person, so treat them as supporting clues rather than proof.
Which sign should you actually rely on?
The key difference is whether a sign predicts ovulation (so you can time things before it) or only confirms it afterwards:
| Sign | What it tells you | Best for |
|---|---|---|
| Egg-white mucus | Your fertile window is open now | Day-to-day timing, predicts ahead |
| Positive OPK (LH surge) | Ovulation likely in 24–36 hours | A clear “go” signal to try |
| BBT rise | Ovulation has already happened | Confirming, learning your pattern |
For timing sex to conceive, the predictive signs — mucus and OPKs — are what matter. BBT is better for understanding your cycle over time than for catching this month’s window.
How to pinpoint your fertile days
You don’t have to track everything. A simple, effective approach:
- Estimate first. Use our Ovulation Calculator to get your likely ovulation day and fertile window from your last period and cycle length.
- Watch your mucus as those days approach.
- Confirm with ovulation tests if you want extra certainty.
Together, an estimate plus one or two body signs is usually all you need.
How often should you have sex in the fertile window?
You don’t need to overthink the schedule. The evidence is reassuring: having sex every one to two days across your fertile window gives the best chance, and every other day is just as effective as every day for most couples — without the pressure. If timing every day feels like a lot, aim for the 2–3 days before ovulation and ovulation day itself.
Try not to “save up” for the big day, either — regular activity through the window beats waiting for one perfectly-timed attempt, since pinning ovulation to the exact hour is impossible.
What if your cycles are irregular?
If your cycle length jumps around from month to month, a calendar estimate alone can miss your window. Lean harder on the real-time signs: track cervical mucus daily, and start using ovulation tests a few days earlier than you think you’ll need to, continuing across a wider stretch of days until you catch the surge. Over two or three cycles you’ll usually see a pattern — and if cycles are very unpredictable or absent, it’s worth checking in with your provider.
When are you most fertile?
To recap: aim for the 2–3 days before ovulation plus ovulation day. If you have regular cycles, that’s often around the middle of your cycle — but everyone is different, which is exactly why the signs above matter more than the calendar alone. Combine an estimate with one body sign you find easy to read, and you’ll catch your window most months without turning it into a chore.
Once you’ve conceived, you can find out when your baby is due with our Due Date Calculator.
This article is for general information only and isn’t medical advice. If you have questions about your fertility or cycle, your healthcare provider is the best person to ask.