How to track ovulation

A cycle’s fertile window is six days long — the five days before ovulation plus ovulation day itself — but pinpointing when that window opens takes more than counting days on a calendar. This guide covers the four tracking methods by accuracy (calendar, cervical mucus, basal body temperature, LH test strips), what each one actually tells you, and how to combine them for a picture that’s reliable enough to plan around — whether you’re trying to conceive or trying to avoid it.

Why the calendar method is a starting point, not an answer

Textbook cycles are 28 days long and ovulation happens on day 14. Real cycles vary — 21 to 35 days is considered normal, and the same person’s cycles often vary 2–7 days month to month. If you predict your fertile window purely by “cycle day 14,” you’ll miss it in any month where you ovulated on day 11 or day 18.

The calendar method works for two things: (1) narrowing the window to a roughly ten-day range worth watching, and (2) a rough rhythm-method failure rate of 15–25% per year if used alone as contraception. Neither is good enough for precise conception planning. It’s table-stakes — use it to know when to start looking, then switch to a body-signal method for the actual window.

Cervical mucus — free, underrated, reasonably accurate

Cervical mucus changes consistency across the cycle. Post-period, most people have little or none (“dry days”). As ovulation approaches, estrogen rises and mucus becomes stretchy, clear, and slippery — the “egg-white cervical mucus” (EWCM) described in fertility literature. After ovulation, progesterone thickens it again quickly.

Peak EWCM is your strongest same-day ovulation signal that’s free and requires no equipment. Most people find it reliable after 2–3 cycles of deliberate tracking, though it takes practice to distinguish EWCM from normal discharge confidently. Perfect use alone as a contraceptive method (the Creighton or Billings systems) has a published failure rate around 1–3% per year — comparable to condoms — but real-world use drifts higher.

Basal body temperature (BBT) — confirmation, not prediction

Body temperature at rest rises by 0.3–0.6°F (0.2–0.3°C) after ovulation, due to progesterone. Track BBT every morning before getting out of bed using a dedicated BBT thermometer (more precise than a regular one), and plot it. Two consecutive days above the pre-ovulation baseline confirms ovulation happened.

Key limitation: BBT confirms after ovulation, so by itself it’s useless for timing intercourse for conception on the fertile day. Its real value is closing the loop — learning your own ovulation day pattern across months so your calendar predictions improve.

LH test strips — the most precise prediction

Luteinizing hormone (LH) surges 24–48 hours before ovulation. Over-the-counter LH test strips (also called OPKs — ovulation predictor kits) detect the surge in urine. A positive means ovulation is likely within the next 12–36 hours. Test daily, starting ~5 days before your expected ovulation day, through the day of the positive.

Accuracy is high — the test itself is around 99% sensitive in clinical studies. The practical catch: some people have LH baseline variation, or PCOS-related elevated LH, that creates false positives. Pair with one other method (EWCM or BBT) for confirmation if you’re getting confusing results across multiple cycles.

Combining methods — “symptothermal”

Using cervical mucus + BBT together (often called the symptothermal method) has one of the best efficacy profiles of any non-hormonal contraceptive method when used perfectly — under 1% failure per year. For conception planning, symptothermal plus LH strips closes every gap: LH strips predict the window opening, EWCM confirms the fertile day in real-time, and BBT confirms afterward that ovulation actually occurred.

The fertile window math

Sperm can live 3–5 days in fertile cervical mucus; the egg is viable for 12–24 hours after ovulation. So the fertile window is effectively the 5 days before ovulation plus ovulation day — 6 days total. Inside that window, conception probability per act of intercourse is highest the day before and day of ovulation (15–30%).

For conception: intercourse every 1–2 days throughout the fertile window maximizes chances. Daily intercourse vs every-other-day doesn’t meaningfully change outcomes. Stressing about perfect timing often causes more problems than the timing itself.

When to see a clinician

Under 35 and trying for 12 months without conception; 35 or over and trying for 6 months; cycles consistently shorter than 21 days or longer than 35 days; or any month without a detectable LH surge across 3+ consecutive tracked cycles. These are the flags for a reproductive-endocrinology or OB-GYN conversation about testing (hormone panels, AMH, semen analysis if applicable).

For day-to-day tracking, use the ovulation calculator to predict your fertile window from cycle data, and the pregnancy calculator once you’re tracking a positive result. This guide is informational — always confirm health decisions with a qualified clinician.