LH Surge

What the LH Surge Measures

Luteinizing hormone (LH) comes from the pituitary gland, and it stays at a low, steady baseline for most of the cycle.^[1] As a follicle matures in the ovary, it produces more estradiol, and once that estradiol holds near its peak level for about two days, it flips from suppressing LH to triggering it.^[1] That flip causes a sharp spike in LH, the surge, which pushes the mature egg through the follicle wall and out of the ovary.^[2]

How It's Measured

The LH surge can be measured directly from blood, but most people track it with a urine ovulation predictor kit (OPK), a test strip that reacts to the LH your kidneys filter into urine.^[4] A test line as dark as or darker than the control line marks a positive result, meaning your LH has crossed the surge threshold that day. LH can also be measured through an at-home fertility monitor or a lab panel, both of which report a numeric value instead of just a positive or negative line.^[5]

Why People Track the LH Surge

The LH surge is the clearest hormonal marker of when ovulation is about to happen. Estradiol and progesterone shift more gradually across the cycle, but LH moves in one sharp, short-lived spike, which makes it easier to catch with a single daily test.^[2]

For how LH fits together with estradiol and progesterone across a full cycle, see our hormone curve explainer.

How Go Go Gaia Tracks the LH Surge

Go Go Gaia lets you log an OPK result with one tap, marking it positive or negative and noting the time you tested. If you use an at-home hormone monitor or get a lab LH panel, you can upload those numeric urine or serum LH values instead, and the app charts them against your logged cycle day. Either way, your LH readings sit next to the rest of your cycle data instead of living in a separate app or a paper log.

What the Research Shows

The surge itself is a reliable predictor of timing. Its onset typically comes about 34 to 36 hours before ovulation, and the peak comes roughly 10 to 12 hours before.^[2] But no two surges look alike. In one study of 107 regularly ovulating women tracked over 283 cycles, LH surges varied widely in shape, some spiking and dropping quickly and others building or tapering over several days.^[3]

A positive OPK confirms that a surge happened, not that ovulation followed it. Research on urinary LH testing notes that some anovulatory cycles still produce a hormone rise big enough to trigger a positive result, including cases where the follicle luteinizes without releasing an egg.^[4] Our at-home hormone test guide covers how OPKs compare with other urine and saliva options.

Related Terms

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

How long after the LH surge do you ovulate?

Ovulation follows the start of the LH surge by about 34 to 36 hours, and it follows the LH peak by about 10 to 12 hours. Timing varies some from cycle to cycle, which is why OPKs work best as a window rather than a single exact day.

Does a positive OPK mean I definitely ovulated?

No. A positive OPK means your urinary LH crossed the test's threshold, which usually reflects a real surge. It doesn't confirm the egg was released, since some cycles produce an LH rise without ovulation actually following it.

Does everyone's LH surge look the same?

No. Research tracking LH surges across hundreds of cycles found they vary widely in shape and length, some rising and falling within a day and others building gradually over several days. That variability is one reason a single test can miss a surge if the timing is off.