Ovulation itself is a single, brief event: usually one egg is released from the ovary, once per cycle. What lasts longer is everything around it: the egg can be fertilised for about 12 to 24 hours, and the fertile window runs for about six days, because sperm can keep the ability to fertilise for up to five days. The NHS puts sperm survival at up to seven days.
So when people ask how long does ovulation last, they are usually asking one of three different questions without realising it. To be honest, I think that mix-up is why the answers online disagree so much.
| What you might mean | How long it lasts | Best source |
|---|---|---|
| The ovulation event (the egg being released) | A single brief event. I could not find a study reporting an exact duration | NHS definition; no duration found in the searches run for this article |
| Egg survival after release | About 12 to 24 hours (guidance); 0.5 days median, 0.7 days in a later overview (models) | ACOG; Royston 1982; Ferreira-Poblete 1997 |
| Sperm survival | Up to five days with fertilising ability (research); the NHS says up to 7 days | NEJM 1995; NHS |
| The fertile window | Six days: the five days before ovulation plus ovulation day | NEJM 1995; BMJ 2000; ASRM 2022 |
Sources: NHS; ACOG; Royston 1982; Ferreira-Poblete 1997; Wilcox et al, NEJM 1995 and BMJ 2000; ASRM 2022. Each is linked in the sections below.
How Long Does Ovulation Last? (Shorter Than Most Pages Suggest)
Ovulation lasts a moment, not a day. The NHS describes it simply as the release of an egg from the ovary, and it happens once in a cycle rather than stretching over several days.
You will see confident figures online for how long the release itself takes. I have not been able to find a primary study behind any of them, so I am not going to repeat one here. "Brief" is as precise as the evidence honestly gets.
The figure most pages give for ovulation, "12 to 24 hours", is actually something else. It is how long the egg survives afterwards.
👉 It wasn't about how long ovulation lasts. It was about how long the egg and the sperm last.
How Long Does the Egg Survive After Ovulation? (About a Day at Most)
After it is released, the egg can be fertilised for about 12 to 24 hours. Dr Barry Witt, a fertility specialist writing for ACOG, the American College of Obstetricians and Gynecologists, explains the timing like this: "This is because sperm can live in a woman’s body for as long as 5 days, while an egg can survive for about 12 to 24 hours after ovulation." ACOG's own patient FAQ says about 24 hours.
It is worth knowing where that number comes from, because it is easy to assume it is an NHS figure, and it isn't. The NHS and NICE pages on this topic do not give an egg lifespan at all. The "12 to 24 hours" rests on ACOG's US guidance, the UK charity Tommy's, and statistical modelling papers.
Those models point the same way, if anything slightly shorter. Royston, in Biometrics in 1982, estimated the egg's median survival at 0.5 days, and a 1997 overview of the models by Ferreira-Poblete put it at 0.7 days. These are estimates fitted to conception data, not direct observation of eggs.
So the honest summary is probably "about half a day typically, a day at the outside".
How Long Is the Fertile Window? (Six Days, Ending on Ovulation Day)
The fertile window is about six days: the five days before ovulation plus the day of ovulation itself. It is much longer than the egg's lifespan because sperm can wait for the egg, and the egg cannot wait for sperm.
Research puts sperm survival at up to five days in the body, the figure behind the fertile window below: the 1995 New England Journal of Medicine study by Wilcox, Weinberg and Baird found sperm keep their ability to fertilise for up to five days. The NHS's own upper estimate is seven days after sex. We have covered the detail separately in how long sperm stay in the body.
That NEJM study is where the six days comes from. It followed 221 healthy women who were planning a pregnancy, across 625 cycles and 192 pregnancies. The authors' conclusion: "Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation."
In 31 of those 625 cycles there was no intercourse inside the six days, and none of them ended in a conception. The American Society for Reproductive Medicine uses the same definition, a six-day interval ending on the day of ovulation.
What Are the Chances of Getting Pregnant on Each Day Around Ovulation? (The Day-by-Day Numbers)
Per cycle, the chance of conceiving rises from about 10% five days before ovulation to about 33% on ovulation day itself, according to the Wilcox, Weinberg and Baird study in the NEJM in 1995. Day by day, the estimates run 10%, 16%, 14%, 27%, 31% and 33%.
| Day of intercourse relative to ovulation | Cycles with intercourse on this day only | Pregnancies in those cycles | Single-day conception rate | Estimated probability of conception (model, all 625 cycles) ± SE |
|---|---|---|---|---|
| Day -6 (six days before) | not in Table 1 | not in Table 1 | not in Table 1 | 0 (95% CI 0 to 0.12), from Results text |
| Day -5 | 12 | 1 | 0.08 | 0.10 ± 0.08 |
| Day -4 | 24 | 4 | 0.17 | 0.16 ± 0.06 |
| Day -3 | 13 | 1 | 0.08 | 0.14 ± 0.08 |
| Day -2 | 28 | 10 | 0.36 | 0.27 ± 0.07 |
| Day -1 | 38 | 13 | 0.34 | 0.31 ± 0.06 |
| Day 0 (day of ovulation) | 14 | 5 | 0.36 | 0.33 ± 0.09 |
| Day +1 (day after ovulation) | not in Table 1 | not in Table 1 | not in Table 1 | 0 (95% CI 0 to 0.12), from Results text |
| Total | 129 | 34 |
Source: Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333(23):1517-21, Table 1 and Results text. 221 healthy women, 625 cycles, 192 conceptions. "Conception" means a pregnancy detected by a very sensitive urine test, so it includes very early losses.
A few things I think are worth reading off that table:
- The three days ending on ovulation day are clearly the best, at 27%, 31% and 33%.
- The small dip three days before (14%, against 16% the day before it) sits well inside the margins of error. I would not read anything into it.
- The day after ovulation is shown as zero, because no pregnancy could be attributed to intercourse on that day. The authors could not rule out a chance of up to 12%, which is what the confidence interval in the table means. If you see a page showing a positive percentage for the day after ovulation and crediting this study, it is not reflecting what the study found.
All of this day-by-day data comes from couples conceiving through intercourse, not insemination. As far as I can find, there is no equivalent day-by-day dataset for home insemination, so treat the numbers as a guide to the shape of the window rather than exact odds.
They also come from healthy couples in their first months of trying. The authors say couples who have been trying for six months or more will, on average, have lower probabilities.
Try It: Chance of Conception by Day
The same NEJM figures as the table above, one day at a time: 10%, 16%, 14%, 27%, 31% and 33% across the six days of the fertile window, and zero estimated for the day after ovulation, with an upper limit of 12%. Pick a day to see where it sits.
Chance of Conception by Day
Pick a day relative to ovulation to see the chance of conceiving in that cycle, using the day-by-day estimates from the 1995 New England Journal of Medicine study in the table above.
Day of ovulation
33%
estimated chance of conception in that cycle
Model estimate 0.33 ± 0.09 (standard error)
The highest estimate in the study, but only just: the day before (31%) and two days before (27%) are almost as good. The window closes after today.
Dashed outline: the day after ovulation is estimated at 0%. The outline marks the 12% the authors could not rule out.
Based on Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333(23):1517-21, Table 1 and Results text. 221 healthy women, 625 cycles, 192 conceptions. "Conception" includes very early losses.
Worth knowing: this data comes from couples conceiving through intercourse. I could not find an equivalent day-by-day dataset for home insemination, so treat it as a guide to the shape of the window rather than exact odds. The couples were healthy and in their first months of trying, and the authors say couples who have been trying for six months or more will, on average, have lower probabilities.
This tool gives general information, not a diagnosis or a prediction for you. See a GP if you have been trying for a year without success, or sooner if you are 36 or over, your periods are irregular, or you have had 6 cycles of insemination without conceiving.
How Long After a Positive LH Test Do You Ovulate? (Usually Within a Day or Two)
After a positive home LH test, ovulation can come at any point in the next two days. The ASRM committee opinion puts it as "ovulation may occur any time within the 2 days thereafter", and it also notes that around 7% of cycles give a false positive.
The more precise figures come from blood tests, not home urine tests. A World Health Organization study from 1980 found a median of 32 hours from the first rise in blood LH to ovulation, with 90% of ovulations falling between 16 and 48 hours after that rise.
A German ultrasound study in Human Reproduction in 2000 found ovulation came 1 day after the blood LH surge in 51.1% of cycles and 2 days after in 43.2%. It never came before the surge.
Both studies measured blood LH, not a home urine test, so any "exactly X hours after a positive" claim is an approximation.
👉 A positive LH test means ovulation is coming, not that it is happening now. And by then you are already inside your best days.
What Does This Mean for Timing Sex or Insemination? (Cover the Days Before)
The practical message is to cover the days before ovulation, not to wait for ovulation day. In the NEJM data, the day before (31%) and two days before (27%) are almost as good as ovulation day itself (33%), and the authors warn that couples who hold off until they have evidence of ovulation may miss earlier chances.
A 1999 re-analysis in Human Reproduction, which corrected for the error in pinpointing ovulation day, actually put the peak on the day before ovulation, with probabilities falling close to zero afterwards.
NICE guideline NG257, published in March 2026, keeps it simple. Vaginal sex every 2 to 3 days gives the best chance of pregnancy, and for people using artificial insemination, the insemination should be timed around ovulation.
For the actual strategy, including what to do on ovulation day itself, see our guide to the best time to get pregnant.
If you would rather hear this from a clinician, Dr Natalie Crawford, a double board-certified OB-GYN and reproductive endocrinologist in the US, covers the fertile window, how long eggs and sperm live, and why calendar-based apps often get ovulation day wrong. She also talks about temperature tracking, so keep in mind that NICE says not to use temperature charts to confirm ovulation.
When Should You See a GP? (The NHS Is Clear on This)
See a GP if you have been trying for a year without success, and sooner if any of the points below apply. This is the NHS and NICE position, and I would not wait past it.
- A year of trying. The NHS says to see a GP if you have not conceived after a year of trying, and NICE NG257 says both partners should be offered assessment at that point.
- Aged 36 or over, or a known or suspected cause. Go sooner. NICE says referral should be offered straight away in these cases.
- Conceiving by insemination. NICE says assessment should be offered after 6 cycles of artificial insemination without conceiving.
- After a miscarriage or ectopic pregnancy. New in the 2026 guideline: the clock carries on, it does not restart.
- Irregular or absent periods. The NHS counts periods as irregular if the gap is less than 21 days or more than 35 days, and says to see a GP if your periods are irregular and you are struggling to get pregnant.
- Ovulation-type pain that is not routine. The NHS says to ask for an urgent GP appointment or call 111 if tummy pain is severe and painkillers have not helped, if it keeps coming back, or if you think you may be pregnant. Similar pain can come from endometriosis, ovarian cysts, STIs or an ectopic pregnancy.
- You cannot have, or find it difficult to have, sex. The NHS lists this as a reason to speak to a GP (NICE NG257 specifically names vaginal intercourse).
Ovulation FAQ (The Questions People Actually Ask)
What are the 7 signs of ovulation?
There is no official list of seven. The signs named by Tommy's are a positive LH ovulation test, cervical mucus that turns thinner and stretchy like raw egg white, a small temperature rise of around 0.2C (which comes after ovulation), one-sided lower tummy pain (which the NHS also describes, lasting from a few minutes to 1 or 2 days), breast pain, bloating, and a higher sex drive or a cervix that feels high and soft. Tommy's is clear that symptoms are not a guaranteed way of predicting ovulation. There is more in our guide to ovulation symptoms.
Can I get pregnant 1 day after ovulation?
It is unlikely, and the best data says close to zero. In the NEJM study of 625 cycles, no pregnancy could be attributed to intercourse after the day of ovulation, although the authors could not rule out a chance of up to 12%. Guidance from ACOG and Tommy's still says pregnancy is possible up to a day after, which reflects the egg's 12 to 24 hour lifespan and the fact that nobody can pinpoint the exact hour of ovulation at home. So do not wait for ovulation. Aim for the days before it.
How do you know when ovulating is over?
You cannot feel the egg's lifespan ending, but there are signs after the fact. Tommy's says basal body temperature rises by around 0.2C after ovulation and stays up until the next period, and cervical mucus stops being thin and stretchy. The clinical test is a blood progesterone level in the mid-luteal phase (day 21 of a 28-day cycle), which NICE recommends to confirm ovulation. NICE also says not to use temperature charts to confirm ovulation, because they do not reliably predict it. A period typically follows 10 to 16 days after ovulation, according to the NHS.
Is ovulation exactly 14 days?
No. In the BMJ study by Wilcox, Dunson and Baird in 2000, among 69 cycles that were exactly 28 days long, ovulation fell 14 days before the next period in only 10%. The gap ranged from 7 to 19 days, so ovulation landed anywhere from day 10 to day 22. Only about 30% of women had their whole fertile window inside days 10 to 17. The authors' advice: "Women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular." The NHS gives a range too, around 10 to 16 days before the next period.
The Bit the Numbers Leave Out (Good Timing Is Not a Guarantee)
Only about 37% of cycles in the NEJM study were capable of producing a conception at all, whatever the timing. These were healthy couples early in trying. The modelled chance per cycle was 37% with daily intercourse and, with no special timing around ovulation, 33% with intercourse every other day and 15% once a week. For live births only, the model gives 25%, 22% and 10%.
I think that is actually the kindest number in the whole paper. Good timing raises the odds. It does not guarantee a cycle.
So if you covered the right days and still got a negative test, that is mostly how the odds work, not something you got wrong.
It is a strange thing to plan your month around an event that lasts a moment. It is tiring, it can take the fun out of things, and it lands on both of you. Go easy on each other.
Keep Reading: Helpful TTC Guides
If this was useful, these go a bit deeper on the parts I only touched on here:
- The best time to get pregnant
- How long do sperm stay in the body?
- Ovulation symptoms: what I missed
- When to take a pregnancy test after ovulation
