What is an ovulation predictor kit (OPK)?
An ovulation predictor kit (OPK) is a home urine test that detects the surge of luteinizing hormone (LH) that comes 24 to 36 hours before ovulation. A positive result means ovulation is likely soon, marking your most fertile days. OPKs come as test strips, midstream sticks and digital readers, some of which also measure estrogen.
How to use an OPK
- Work out when to start: usually about 17 days before your next expected period. Our ovulation test calculator does the maths.
- Test once a day, or twice if your surge may be short. Many people test in the early afternoon.
- Avoid drinking a lot of fluid for 2 hours beforehand, which can dilute the result.
- Read the result in the time the instructions give.
Reading the result
| Result | What it means |
|---|---|
| Test line lighter than control | Negative: no surge yet |
| Test line as dark as, or darker than, control | Positive: LH surge, ovulation likely in 24 to 36 hours |
| Digital smiley or solid symbol | Positive, per the brand's instructions |
Unlike a pregnancy test, a faint line on an OPK is negative. Your best days for conception are the day of the positive and the next 1 to 2 days.
Limits to know
- A positive shows the surge, not that ovulation actually happened.
- With PCOS, high LH can give several positives.
- Perimenopause, some fertility medicines and recent pregnancy can affect results.
- OPKs help with conception, not with avoiding pregnancy.
Pair OPKs with cervical mucus or basal temperature for a fuller picture. Learn more in luteinizing hormone.
Frequently asked questions
How accurate are ovulation tests?
They are very good at detecting the LH surge, but a surge doesn't guarantee ovulation. Confirming with a temperature rise helps.
Can an OPK detect pregnancy?
Sometimes it turns positive in pregnancy because LH and hCG are similar, but it isn't designed for that. Use a pregnancy test.
Sources
- MedlinePlus: Ovulation home test
- MedlinePlus: Luteinizing Hormone (LH) Levels Test
- ACOG: Fertility Awareness-Based Methods of Family Planning
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
Ovulation test calculator: when to start testingFree ovulation test calculator: enter your last period and cycle length to see the day to start LH tests, plus the best time of day to test. Any brand.
What is the LH surge?The LH surge is a sharp rise in luteinizing hormone that triggers ovulation about 24 to 36 hours later. Timing, testing, and what it means for fertility.Luteinizing hormone (LH): definition and meaningLuteinizing hormone (LH) is a pituitary hormone that triggers ovulation and supports progesterone. Normal levels, the LH surge and what tests show.How do you track ovulation?How to track ovulation: calendar estimates, LH tests, cervical mucus, temperature and wearables. What each tells you and how to combine them.
Signs of ovulation: definition and meaningSigns of ovulation are body changes around egg release: stretchy mucus, a temperature rise, LH surge and more. What each one means and how to read them.