Ovulation Tracking — Calendar vs LH Sticks vs Ultrasound

Knowing exactly when you ovulate is fundamental to natural conception and fertility planning. This page compares the major ovulation tracking methods, calendar, basal body temperature, LH urine sticks, cervical mucus and ultrasound, and helps you choose the right method for your situation.

1. The calendar method

Calendar-based estimation: ovulation occurs about 14 days before next period in regular cycles. For a 28-day cycle, ovulation is around day 14. For shorter cycles (24–26 days), around day 10–12. For longer cycles (32 days), around day 18. Useful as starting framework; unreliable for irregular cycles or precision timing.

2. Basal body temperature (BBT)

BBT rises 0.2–0.5°C after ovulation due to progesterone effect. Measured first thing in morning with accurate thermometer. Useful for confirming ovulation has occurred but does not predict it in advance. Wearables (Tempdrop, Oura) automate measurement and reduce error.

3. LH urine sticks (OPKs)

Detect LH surge, which precedes ovulation by 24–36 hours. Test once daily from approximately day 10 in 28-day cycle. Positive test signals ovulation within a day. Reliable in regular cycles; less so in PCOS (chronic high LH) or premature ovarian insufficiency. Digital tests reduce interpretation error.

4. Cervical mucus monitoring

Cervical mucus changes through cycle. Around ovulation: clear, slippery, stretchy (“egg white”). After ovulation: thicker, opaque, sticky. Requires consistent observation and some experience. Useful in conjunction with other methods; less precise alone.

5. Ultrasound monitoring

Most precise method. Serial transvaginal ultrasounds (every 2–3 days from day 8) track follicle growth. Ovulation predicted when dominant follicle reaches 18–20 mm. Confirms ovulation by follicle collapse. Used for natural-cycle IUI, timing of frozen embryo transfer, and unexplained subfertility evaluation.

6. Wearable devices

Continuous BBT monitoring (Tempdrop), heart rate variability tracking (Ava), oxygen saturation (Oura) — increasingly accurate for ovulation prediction in regular cycles. Combine multiple signals for improved precision. Cost-effective compared to repeated ultrasounds for natural conception planning.

7. Which method for which situation

Regular cycles, trying to conceive: combine calendar + OPK + cervical mucus. Irregular cycles or PCOS: ultrasound is most reliable. Confirming ovulation has occurred: BBT or progesterone blood test. IUI or planned timing: ultrasound + trigger if needed. Unexplained subfertility: full evaluation often needed.

8. Common errors and pitfalls

Testing OPKs in first morning urine (misses early surges). Confusing pre-ovulation rising LH with surge. Assuming regular cycles when irregular. Over-reliance on apps with insufficient data. Confusing implantation spotting with cycle start. Better methods than apps for couples beyond first 3–6 months of trying.