How Long After Your LH Surge Do You Ovulate?

by | Jun 26, 2019

When does ovulation actually happen?

Ovulation and LH Surge

When trying to understand when your fertile and infertile days in your cycle, it’s important to understand how long after your LH surge you ovulate. Ovulation happens when an egg is released from an ovary. For healthy women, it usually happens once every menstrual cycle. The length of a menstrual cycle varies from cycle to cycle, and woman to woman. It usually ranges from 23 to 37 days. Ovulation time varies as well. Women can ovulate as early as day 8 of their cycle, or as late as day 21 [1]. Many women believe they ovulate on day 14, but this is considered the average, not necessarily what happens every month. Finding the timing of your ovulation by simply logging your period on an app may not be enough to accurately determine exact timing as well. Assuming a regular cycle, it could take more than one year of continuous logging to ensure the calendar method becomes accurate for ovulation prediction.

What do Estrogen and LH surges mean in relation to ovulation?

A few days after the period, your body starts to produce a hormone called estrogen. Estrogen helps to increase the thickness of uterus wall and creates a mucus environment that is sperm friendly. Since healthy sperm can live up to 4 days within women’s mucus, and estrogen usually starts to increase about 4-5 days before ovulation, estrogen is a good predictor of fertile window. You become more fertile when you get closer to the ovulation day. High estrogen level triggers a sharp increase of around hormone called luteinizing hormone (LH). This is considered the “LH surge”. The LH surge triggers the release of a mature egg from the ovary, which is what we know as “ovulation”. All in all, estrogen surges triggers the LH surge, which in turn leads to ovulation.

The LH surge is a rather sharp change of the hormone and lasts very briefly. Given that inter-woman and inter-cycle hormone variability is huge, that’s part of the reason why it’s not uncommon for women to miss the LH peak when testing using OPK’s (ovulation prediction kits). According to a study [1], the LH peak value could be as low as 20 IU/L, or as high as 75 IU/L, for health women. OPK uses a fixed hormone threshold to determine + or -, or a “smiley face” vs. “no smiley face”. Without adjustment towards personal variability, missed peak or prolonged “high” is likely to happen.

Ovulation LH Surge Chart

24-36 hours after LH surge, ovulation usually happens. LH is a good indicator of ovulation and your peak fertility days. It then decreases sharply. The entire LH surge lasts about 2 days.

The Egg lives up to 24 hours after ovulation. Beyond 24 hours, the chance of conceiving is zero [2]. Your fertile window starts from the day of Estrogen surge, reaches peak fertility at LH surge, and ends at 24 hours after ovulation. Body temperature increases 12 hours after ovulation, so it identifies the last 12 hours of fertile window instead of capturing the entire 6 days.


Estrogen & LH Chart

The best ways to test Estrogen and LH Levels to predict ovulation

There are multiple ways to test for Estrogen and LH, including:

  • Blood test from a doctor – This is the most accurate method. However, it requires you to visit the lab for every test. For people trying to conceive (TTC) or trying to avoid pregnancy (TTA), it usually requires 10-15 tests per month, which could be troublesome. You can reduce the number of tests slightly, but it increases the chance of missing the ovulation as you may not ovulate on the exact same day every cycle.
  • Testing at home with an OPK – A positive result means you are above the hormone threshold set by the OPK manufacturer, which is usually based on population average, and a negative result means you are below. However, a positive or negative result may not necessarily mean you are ovulating or not, due to huge inter-woman hormone level variabilities. You would also need to log down the daily OPK results manually, which could be troublesome and stressful.
  • Smart hormone tracker – Mira is palm-sized hormone tracker which tracks and shows you your actual hormone concentration with the accuracy of hospital-grade lab equipment. It is intended for home use. Mira measures your LH, Estrogen, and other female hormone concentrations in urine. The data is automatically synced with the Mira App, which optimizes the ovulation prediction based on your personal health. It is accurate, easy to use, and smart.

Testing your hormones to predict ovulation? Mira takes the guesswork out by measuring your actual fertility hormone concentrations! Sign up today for exclusive Mira content and discounts!
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When to test Estrogen and LH levels?

If you are trying to conceive (TTC) or trying to avoid (TTA), it is the best to start early during a cycle. As cycle length and ovulation date could vary, starting early could reduce the risk of missing fertile days. However, testing more frequently is associated with high cost. Mira’s artificial intelligence learns your cycle and tells you when to test only when it is needed. Mira helps you to avoid missed fertile days while not wasting any tests at the same time.


  • Ovulation timing varies! A woman could ovulate on as early as day 8 of her cycle, or as late as day 21.
  • Estrogen and LH surges are the triggers and causes of ovulation. Testing Estrogen and LH levels are the most accurate home use ways to detect an ovulation.
  • Your fertile window starts from the day of Estrogen surge, reaches peak fertility at LH surge, and ends at 24 hours after ovulation. 24-36 hours after LH surge, ovulation usually happens.
  • Since hormone levels differ from woman to woman, and cycle to cycle, it is the best to use an accurate and personalized way to test hormones. It should also be easy to use for long term.


  1. Häggström, Mikael (2014). “Reference ranges for estradiol, progesterone, luteinizing hormone and follicle-stimulating hormone during the menstrual cycle”. Wikiversity Journal of Medicine 1 (1). DOI:10.15347/wjm/2014.001. ISSN 20018762
  2. Wilcox AJ. “Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby”. New England Journal of Medicine. (1995) 333:1517


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Ready to easily, precisely, and automatically track your ovulation cycles? Let Mira take the guesswork out of getting pregnant, so you know exactly when to conceive.

Reserve Your Mira Today

Ready to easily, precisely, and automatically track your ovulation cycles? Let Mira take the guesswork out of getting pregnant, so you know exactly when to conceive.