The LH Surge, Explained: What It Tells You About Ovulation and What It Does Not

The LH surge is a short, sharp rise in luteinising hormone that tells a mature follicle to release its egg. Ovulation usually follows within about a day and a half. It is a signal, not proof: a surge does not confirm an egg was released, and it arrives near the end of your fertile window, not the start.

‍

Question	Short Answer
What LH is	Luteinising hormone, one of the two pituitary hormones that control the ovaries. The other is follicle-stimulating hormone (FSH).
Where it is made	The pituitary gland, a pea-sized gland at the base of the brain.
What triggers the surge	Rising estrogen from the dominant follicle as it matures.
Time from surge to ovulation	Usually about 24 to 36 hours after the surge starts, and sooner after it peaks.
How long the surge lasts	About two days from start to finish in blood; in urine it usually shows for one to two days.
What it can tell you	That your body has signalled ovulation and ovulation is probably close.
What it cannot tell you	Whether an egg was actually released, how healthy the egg is, or whether you are pregnant.

‍

What is the LH surge?

Luteinising hormone (LH) is made by the pituitary gland, a small gland at the base of the brain. It is present in small amounts throughout your cycle and works with follicle-stimulating hormone (FSH) to support the follicles in your ovaries. A follicle is the small fluid-filled sac that holds an egg.

Early in the cycle, the brain keeps LH release in check. As one follicle pulls ahead of the others, it makes more and more estrogen. Once estrogen has stayed high for long enough, the brain switches from holding LH back to releasing a large burst of it. That burst is the LH surge.

The surge does two jobs. It finishes maturing the egg inside the follicle, and it starts the changes that weaken the follicle wall so the egg can be released. It also begins turning the emptied follicle into the corpus luteum, the structure that makes progesterone after ovulation. The surge happens alongside other changes you may notice, such as clearer cervical mucus; our guide to the physical signs that you are fertile covers those.

Which hormone triggers ovulation?

Luteinising hormone (LH) triggers ovulation. It does not work alone, though. Four hormones act in sequence, and the LH surge triggers the release of the egg. The table below shows what each hormone does, and answers the common question of how LH and FSH differ.

‍

Hormone	Made By	Its Job Around Ovulation
Follicle-stimulating hormone (FSH)	Pituitary gland.	Stimulates the growth of a group of follicles early in the cycle so one can become the lead follicle.
Estrogen	The growing follicles, mainly the lead one.	Builds the womb lining and makes cervical mucus clearer; once high enough, it triggers the LH surge.
Luteinising hormone (LH)	Pituitary gland.	Surges to finish maturing the egg and trigger its release from the follicle.
Progesterone	The corpus luteum, after ovulation.	Rises after ovulation to prepare the womb lining for a possible pregnancy.

‍

When does the LH surge happen in your cycle?

The LH surge happens in the day or two before ovulation, so its timing depends on when you ovulate, not on a fixed date on the calendar. In a 28-day cycle, ovulation often falls around the middle, so the surge usually happens around day 12 to 14. That is a common pattern, not a rule.

What moves most is the first half of the cycle, called the follicular phase, while the follicle grows. The second half, from ovulation to your next period, usually changes less and lasts about two weeks. So in a 24-day cycle the surge may come around day 9, while in a 35-day cycle it may not arrive until about day 20. Even women with regular periods do not ovulate on exactly the same day every month.

This is why counting to day 14 so often misses the surge. The surge follows your follicle, not the calendar, and sometimes a late or early month is normal.

How long after the LH surge do you ovulate?

Ovulation usually happens about 24 to 36 hours after the LH surge starts, and sooner after the surge peaks, often within about 10 to 24 hours. The difference matters because the start and the peak are not the same moment, and many sources quote a single number without saying which one they mean.

The most detailed evidence comes from a World Health Organization study published in 1980, which matched blood hormone levels against direct inspection of the ovaries. The median gap was about 32 hours from the first rise in LH and about 16 to 17 hours from the peak. Across individual women, however, the range was far wider: 24 to 56 hours from the first rise, and 8 to 40 hours from the peak. A typical figure is useful, but it cannot tell you when your egg is released.

The surge is not the start of your fertile window. The fertile window is the six days that end on ovulation day, because sperm can survive for several days while the egg lives for only about a day. In the landmark study of this window (Wilcox and colleagues, 1995), the chance of conception rose from about 10 percent five days before ovulation to about 33 percent on ovulation day, with the best days being the two days before ovulation and ovulation day itself. By the time the surge appears, most of the window has already passed. The surge tells you the window is closing, not opening. Sex on the day of the surge and the day after is still well timed, but sex in the days before it counts just as much.

How long does an LH surge last?

An LH surge often lasts about one to two days, though the pattern varies more than most guides admit. A small, closely sampled study (Hoff and colleagues, 1983) found an average blood surge of about 48 hours: a steep climb over roughly 14 hours, a plateau of about 14 hours, then a slower fall over about 20 hours. Urine shows the change a little later than blood, usually for 1 to 2 days.

A larger study of 283 cycles in normally fertile women (Direito and colleagues, 2013) found that surges varied widely in shape, height, and length. Some rise and fall within a day, some rise in two steps, and some stay raised for several days. A short surge can easily fall between two checks and be missed, even in a cycle where ovulation happens normally.

Does an LH surge mean you have ovulated?

No. The LH surge signals the release of the egg. It doesn't prove the egg was released. In most cycles, ovulation follows as expected, but the signal and the event are different, and the surge only shows the first.

Occasionally, the follicle responds to the surge and starts making progesterone but never ruptures, so the egg stays inside. This is called a luteinised unruptured follicle. In other cycles, particularly with polycystic ovary syndrome (PCOS), LH can rise without a mature follicle ready to respond.

Doctors confirm ovulation in two main ways. A progesterone blood test in the second half of the cycle, roughly a week after the expected ovulation, shows whether the hormone rise that normally follows ovulation has happened; it is best timed to your own cycle rather than to a fixed day 21. A follicle-tracking ultrasound shows the lead follicle growing and then collapsing once the egg is released. Because a luteinised unruptured follicle can still make progesterone, the scan is the more direct way to see that release really happened.

If you want certainty rather than a best guess, follicular monitoring at Cloudnine Fertility tracks your lead follicle through the cycle and shows whether and when you ovulate.

Can you have more than one LH surge in a cycle?

Yes. Some cycles show more than one rise in LH, or a rise that climbs, dips, and climbs again before ovulation. Hormone studies in normally fertile women describe single peaks, double peaks, and plateaus, all in cycles that went on to ovulate. A surge with two peaks is sometimes called a biphasic surge.

Two surges do not mean two eggs, and they are not a sign of twins. Releasing two eggs, the route to non-identical twins, depends on two follicles maturing, not on how many times LH rises. On its own, a double surge is also not a sign that something is wrong.

Mention it to a doctor if you see confusing patterns repeat across three cycles, such as several separate rises, very long runs of high readings, or rises not followed by a period at the expected time. These can point to cycles where ovulation is delayed or not happening, which is common with PCOS.

Why you might not see an LH surge

Not seeing a surge does not always mean you are not ovulating. Sometimes you simply miss the surge; sometimes ovulation is late, paused, or affected by another condition. The table groups the usual reasons with a sensible next step for each.

‍

Situation	What May Be Happening	What to Do
The surge was short	It rose and fell between two home checks, so it was missed even though you ovulated. This is common when you use strips without a record of your cycle length.	See our ovulation test kit guide.
Irregular or long cycles	Ovulation comes later than expected, or not every month.	Note your cycle lengths for a few months. See a specialist if cycles are often shorter than 24 days or longer than 38 days.
Not ovulating that cycle	Illness, stress, a big change in weight or very intense exercise can pause ovulation for a cycle.	One quiet cycle is common. Three in a row needs a check.
PCOS	LH can run high for much of the cycle, giving constant or confusing results without ovulation.	Read the note on PCOS below the table.
Breastfeeding	The hormones that support milk production hold ovulation back.	Expected. Ovulation usually returns as feeds reduce; speak to your doctor if you are trying to conceive.
Perimenopause	Baseline LH rises as the ovaries age, which blurs the surge.	Talk to a fertility specialist, particularly if you are over 40 or your cycles are changing.
Some hormonal medicines	Hormonal contraception and some other hormone treatments suppress the surge or change readings.	Check with the doctor who prescribed them.

‍

A note on PCOS. PCOS is one of the most common reasons women in India see persistently positive or confusing LH results. LH can stay raised for much of the cycle, so a positive reading may not mean ovulation is near. You can still conceive with PCOS, often with support to ovulate; our PCOS and fertility guide explains the options.

Can an LH surge mean you are pregnant?

No. LH is not the pregnancy hormone, and an LH surge cannot tell you whether you are pregnant. The question comes up because LH and hCG, the hormone a pregnancy makes, are chemically very similar, so a test designed for one can sometimes react to the other. That is a quirk of chemistry, not a sign of pregnancy. If your period is late or you think you may be pregnant, take a pregnancy test, which is designed to detect hCG.

How is the LH surge tracked?

There are five common ways to follow the events around ovulation. Only two measure LH itself, and only one shows that ovulation actually happened. The table compares them side by side.

‍

Method	What It Measures	Before or After Ovulation	Setting	Where to Read More
Urine LH strips	LH in urine.	Before: predicts ovulation is near.	At home.	Ovulation test kit guide
Blood LH test	LH in blood at one moment, read against your cycle day by a doctor.	Around ovulation: a snapshot.	Clinic or lab.	Fertility diagnosis guide
Follicle-tracking ultrasound	Follicle growth, then collapse after release.	Before and after: confirms release.	Clinic.	Follicular monitoring
Basal body temperature	The small temperature rise caused by progesterone.	After: confirms it has passed.	At home.	Ask your specialist to review a chart.
Cervical mucus	Clear, stretchy mucus as oestrogen rises.	Before: signals the fertile window.	At home.	Cervical mucus guide

‍

A single blood LH result is a snapshot rather than a pattern, which is why this page does not list LH reference ranges. A doctor reads the result against the day of your cycle and your other results.

The LH surge in fertility treatment

In fertility treatment, doctors either work with your natural LH surge or replace it. In a monitored natural cycle, and in many cycles of intrauterine insemination (IUI), the team watches for the natural surge and times sex or insemination around it. Where more control is needed, a trigger injection is given instead. It does the surge's job, finishing egg maturation and setting the timing of release, so that insemination or egg collection can be planned precisely.

In IVF, medicines are also used to stop an early natural surge, so that eggs are not released before collection. The hormones that grow the follicles in the first place are explained in our guide to gonadotropin injections in IVF. Your specialist chooses the approach based on your cycle, diagnosis and treatment plan.

How Much Does Ovulation Testing Cost in India?

Confirming ovulation usually means a blood test, an ultrasound scan, or both. Costs vary by city, centre and the number of visits a cycle needs, so the table gives indicative ranges where we have them and marks the rest for confirmation.

‍

Test	What It Tells You	Indicative Cost	Notes
Mid-luteal progesterone blood test	Whether the progesterone rise that follows ovulation happened.	Rs. 800 to Rs. 1,500	A single blood draw, timed to your own cycle.
Blood LH test	Your LH level at one point in the cycle.	Rs. 400 to Rs. 1,000	Often part of a wider hormone panel.
Single transvaginal ultrasound scan	Follicle size, or signs that the follicle has collapsed.	Rs. 1,000 to Rs. 3,500	One scan only; a full tracking cycle needs several.
Follicular monitoring (a series of scans in one cycle)	How the lead follicle grows and whether it ruptures.	Rs. 3,000 to Rs. 6,000	The number of scans depends on your cycle length and regularity.

‍

What changes the total: how many scans your cycle needs, whether tests are combined into a single fertility assessment visit, and which city you are in.

When at-home tracking is not enough

Tracking the surge is a reasonable first step, but it has limits. See a fertility specialist if any of the situations below apply to you. The thresholds match those used across our ovulation guides.

‍

Situation	Why It Matters
No surge seen for three cycles in a row	You may not be ovulating regularly.
Cycles often shorter than 24 days or longer than 38 days	Outside the normal range for cycle length, and often linked to irregular ovulation.
Periods have stopped for three months or more, and you are not pregnant	The cause needs to be found.
Trying for 12 months without pregnancy, or 6 months if you are 35 or older	The standard point to begin a fertility assessment.
Confusing LH patterns that repeat across three cycles	Ovulation may be delayed or not happening.

‍

A specialist can confirm whether you are ovulating with a blood test or follicular monitoring, look for the cause if you are not, and agree a plan with you. You can book a consultation at any Cloudnine Fertility centre.

Seek care promptly

See a doctor promptly if: your periods stop for three months or more; you bleed between periods or after sex; you have severe or one-sided pelvic pain around mid-cycle; or you have a positive pregnancy test together with pain or bleeding.

‍

‍