How to Read an Ovulation Test (and What a Positive Looks Like)

Reading an ovulation test seems simple until you are holding a strip with a pale second line. The rule is different from a pregnancy test, and getting it wrong is the most common reason people think they missed, or found, their surge. Here is how to read line strips, digital tests and app readings.

How to read an ovulation test strip

Every line strip has two lines:

• Control line (C): shows the strip worked. It should always appear.
• Test line (T): reacts to luteinizing hormone (LH). It gets darker as LH rises.

Compare the test line with the control line, not with blank paper.

A positive means you are likely to ovulate in the next 24 to 36 hours, according to MedlinePlus, though this is not true for everyone.¹ ACOG gives a range of 24 to 48 hours.¹¹

What does a positive ovulation test look like?

On a strip, a positive is two lines where the test line matches or beats the control line in darkness. It does not need to be dramatically darker; equal counts. On the days before, you will often see the test line get gradually darker, then match the control, then fade again over the following days; in one study, more than half of surges built up over 2 to 6 days.⁴

On digital tests, the display does the comparison for you:

• Clearblue Digital: a smiley face means your LH surge was detected; a blank circle means it was not.⁸
• Clearblue Advanced Digital: a blank circle is low fertility, a flashing smiley is high fertility (estrogen rising), and a static smiley is peak fertility (LH surge).⁹

In the Premom app, the reading is an estimated LH number from 0 to 65 mIU/mL with a Low, High or Peak label.¹⁰ Peak is the equivalent of a positive strip.

Is a faint line on an ovulation test positive?

No. A faint test line on an ovulation test is negative. Your body produces some LH throughout the cycle, so a sensitive strip often shows a light test line on ordinary days. Only a test line as dark as the control means the surge has started.

This is the reverse of a pregnancy test, where any visible test line in the time window usually means hCG was detected. Mixing up the two rules is a common source of confusion; our page on whether an ovulation test can be positive if you are pregnant explains why the two tests behave differently.

How common is misreading? In a study funded by Clearblue's maker, volunteers reading line ovulation tests agreed with a trained technician only 64% to 84% of the time, depending on the brand, against 97% for a digital test.³ If you find line comparison stressful, a digital test or app reading may be worth the extra cost.

How long to wait before reading

Read the test inside the window in its leaflet, and not after. Easy@Home, for example, says to read at 5 minutes and not after 10 minutes.² Lines that appear or darken after the window has closed are not a reliable result. Set a timer.

Tips for a fair comparison

• Test at the same time each day, so you compare like with like; see when to take an ovulation test.
• Do not drink large amounts of fluid before testing.¹
• Lay strips flat and photograph them in the same light, or tape them in order on a card. A row of strips makes the darkening trend easier to see than any single strip.
• Use a new strip every time.

Why you might see several positives

One positive followed by fading lines is the classic pattern, but not the only normal one.

• The surge can last more than a day. In daily urine samples from 46 women with regular cycles, surges came as a single spike in about 42% of cycles, in two phases in 44% and as a plateau in 14%.⁴ Two or three positive days in a row is common with biphasic or plateau surges.
• LH can blip and fall back. In an analysis of 283 ultrasound-checked cycles, a day at 25 mIU/mL or more was followed by three negative days before ovulation in 31% of cycles.⁵ If you get a positive and then negatives, keep testing.
• Some positives are false. ASRM notes that about 7% of cycles give a false-positive LH result.⁶

Repeated positives across much of the cycle are a different signal. In a study of women with PCOS, 75% of those who had not recently ovulated had raised LH levels.⁷ The fertility medicine clomiphene also increases LH and can turn tests positive.¹ Pregnancy can do it too, because hCG shares part of its structure with LH.¹² If your tests are positive most days, a test that measures more than LH, such as progesterone (PdG), can tell you more.

What a negative month means

No positive all cycle does not prove you did not ovulate. You may have missed a short surge between tests, tested with dilute urine, or started too late. MedlinePlus notes you can miss the surge if you skip a day, and that irregular cycles make it harder to detect.¹ Try twice-daily testing near your expected surge next cycle, and start a few days earlier; the ovulation calculator can help.

When to talk to a doctor

Talk to your doctor if you cannot detect a surge or do not become pregnant after using kits for several months.¹ ACOG recommends an infertility evaluation after 1 year of trying, after 6 months if you are older than 35, and right away if you are older than 40.¹¹ Problems with ovulation are the most common cause of female infertility, and a doctor can check whether you ovulate.¹¹ For the rest of the timing picture, see the Try step.