Ovulation Predictor Kits: How to Use LH Tests

Guides. Updated October 11, 2026. Calculated with the standard pregnancy dating method used by ACOG and the NHS.

Ovulation predictor kits detect the surge in luteinising hormone (LH) that triggers ovulation 24 to 36 hours later.

When to start

Start testing a few days before your expected ovulation day. For a 28-day cycle, that's around day 10 or 11; for longer cycles, later.

Reading the result

A positive result means the test line is as dark as or darker than the control line. Your most fertile days are the day of the positive result and the following day.

Limits

Some conditions, including PCOS, can cause LH levels to be high without ovulation, which can make results confusing.

This article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.