Trying to Get Pregnant? Here’s When to Have Sex

There’s a lot of conflicting advice out there about trying to conceive and a surprising amount of it is wrong. People are told to try on day 14 (not always accurate), to lie down afterwards (not necessary), or that it should happen quickly if nothing’s wrong (not always the case).

This guide cuts through the noise. It covers when in your cycle to time sex for the best chance of conceiving, how conception odds actually work, what might be affecting your chances, and importantly, what to do when things aren’t going as planned.

Quick Facts

• Your fertile window is a six day window per cycle, the five days before ovulation plus the day of ovulation. 
• Research finds that most conceptions occur from sex in the two to three days immediately before ovulation.
• Ovulation occurs 12–16 days before your next period, not on day 14 unless your cycle is exactly 28 days.
• Having sex every 2–3 days throughout the cycle is the evidence-based recommendation; this ensures viable sperm are present at ovulation without the pressure of perfectly timed sex.
• Around 80% of couples under 35 with no underlying issues conceive within 12 months. The standard threshold for investigation is 12 months (or 6 months if 35 or over), but earlier investigation is warranted with cycle irregularities or symptoms.
• A Hertility Hormone & Fertility Test before or during your TTC journey gives you real, actionable information rather than symptom-guessing and can significantly shorten the time between concern and clarity.

When in the menstrual cycle are you most likely to conceive?

You can only conceive during a six-day window in each menstrual cycle. This is called the fertile window, and it consists of the five days leading up to ovulation plus the day of ovulation itself. Outside of this window, the chances of pregnancy from unprotected sex is very low

This window exists because of how long sperm and eggs survive in the body. Once released, an egg lives for just 12–24 hours. Sperm, on the other hand, can survive in the female reproductive tract for up to five days. That means sex in the days before ovulation can still result in conception, the sperm are already waiting when the egg arrives.

When does ovulation happen?

Ovulation doesn’t always happen on day 14. This is one of the most widespread and consequential misconceptions in fertility. Day 14 only applies to a textbook 28-day cycle. Latest research shows that ovulation actually occurs approximately between day 12 to 16 days for most people which means:

• On a 24-day cycle, ovulation may happen as early as day 8–12
• On a 28-day cycle, ovulation typically falls around day 12–16
• On a 35-day cycle, ovulation may not happen until day 19–23

If your cycles are irregular, ovulation timing can shift considerably from month to month. Using day 14 as your anchor when your cycle doesn’t conform to that pattern is one of the most common reasons people miss their fertile window.

Hertility’s own research based on data from over 97,000 women actively trying to conceive, found that more than 41% could not accurately identify their fertile window, making this the single most common correctable barrier to natural conception.

What are the chances of getting pregnant during the fertile window?

The odds of conception are not equal across all six days of the fertile window, they build as you approach ovulation and peak just before the egg is released.

Research shows that the two to three days immediately before ovulation carry the highest probability of conception. sex on the day of ovulation is less effective than the day before. Waiting until you’ve confirmed ovulation has occurred may mean you’ve already passed the peak window. This is why covering the full window matters, rather than pinpointing a single “best day.”

How do you know when you’re ovulating?

To make the most of your fertile window, you need to know when ovulation is approaching. There are several ways to identify it.

The most reliable real-time indicator is a positive LH test (ovulation predictor kit), which typically detects the LH surge 24–36 hours before ovulation.  A positive test is your cue to prioritise sex in the next one to two days. They’re the most accurate day-to-day predictor available over the counter. One caveat: if you have PCOS, elevated LH throughout the cycle can produce false positives – see our PCOS and TTC guide for more on this.

Egg-white cervical mucus, clear, slippery, and stretchy is another strong sign that ovulation is approaching. Basal body temperature (BBT) rises slightly after ovulation due to rising progesterone. The limitation is that this confirms ovulation has already happened, so it’s more useful for understanding your cycle pattern over time than for timing sex in the moment.

Day 21 progesterone blood test A blood test measuring progesterone around day 21 of a 28-day cycle (or 7 days after suspected ovulation on other cycle lengths) can confirm whether ovulation has taken place. If your result is low or borderline, it may indicate that ovulation didn’t occur that cycle or that the timing of the test missed the progesterone peak. 

Cycle tracking apps estimate your fertile window from past cycle data, a reasonable starting point for people with regular, predictable cycles, but they’re predictions, not measurements. They don’t account for cycle-to-cycle variation, stress, illness, or travel. Treat them as a guide, not a guarantee.

For a full comparison of all methods, including their reliability and what works best for different cycle types, see: How to detect ovulation.

Should you time sex around ovulation to increase chances of conceiving?

Not necessarily, and for many couples, trying to time sex precisely creates more stress than it solves.

The current clinical recommendation from NICE is sex every 2–3 days throughout the cycle. This ensures viable sperm are consistently present, without the need to nail down your ovulation date precisely. It also removes the pressure of “we have to do it tonight“, which, for many couples, is easier on the relationship and the sex itself.

Something that often goes unsaid in clinical guides is that trying to conceive can make sex feel like a task. Scheduled, clinical, performance-driven. Timed sex can be hard on relationships, and the longer it goes on, the harder it gets.

Something often left unsaid is that trying to conceive can make sex feel like a task. When the approach of a fertile window feels like a countdown, and sex begins to feel like a performance, that affects intimacy. It’s normal and it’s worth acknowledging. Timed sex doesn’t have to mean joyless sex, but if TTC is creating real tension around intimacy, that’s worth talking about, with your partner, and if it persists, with a professional.

For some people, there are physical factors that make sex difficult or painful, including conditions like endometriosis, vaginismus, or vulvodynia. These conditions are underdiagnosed and often poorly supported, but they are treatable. If sex is painful, irregular, or difficult, this is not something to push through silently, it’s information worth sharing with a clinician, because it can be investigated and addressed.

Should you only have sex on your fertile days?

No. Restricting sex to the fertile window alone isn’t the best strategy for two reasons.

First, ovulation timing isn’t always exact, even with tracking, cycles can shift. If you only try during your estimated fertile window and ovulation is a few days later than expected, you may miss it entirely.

Second, sperm quality benefits from regular ejaculation. Infrequent sex can mean a higher proportion of older, less motile sperm are present when the fertile window finally arrives. Having sex regularly throughout the cycle keeps sperm in better condition.

The approach that tends to work best over a sustained TTC journey is regular sex throughout the cycle, with awareness of the fertile window but not controlled by it. Protecting intimacy isn’t just good for the relationship, it sustains the capacity to keep going when the process takes longer than expected.

Are certain sex positions better for conceiving?

No. This is yet another persistent myth in TTC, and the evidence is clear, no sexual position has been shown to improve the chances of conception.

Sperm begin moving through the cervix within seconds of ejaculation, regardless of body position. The ideas that deeper penetration positions help, that lying on your back or elevating your hips afterwards makes a difference, or that you need to stay still for a certain amount of time, none of these are supported by evidence.

The one thing that does make a practical difference is lubrication. Standard lubricants, including saliva may reduce sperm motility and are best avoided when TTC. If you need lubrication, choose a product specifically formulated to be sperm-friendly.

What are your chances of getting pregnant naturally  and how does age affect this?

Even with perfect timing, conception in any given cycle isn’t guaranteed. The chance of conceiving in a single cycle is around 20–25% for people in their mid-20s to early 30s , lower than most people expect, and it explains why most couples don’t conceive in the first month, even when everything is working as it should. 

Conception rates decline with age, primarily because egg quality and quantity reduce, most significantly from the mid-30s onwards.

These are population averages. Individual variation is significant, a 38-year-old with regular ovulation and hormones in range has different odds from a 38-year-old with diminished ovarian reserve. Age matters, but it is one variable among several.

If you’re in your mid-30s or older and thinking about having children, understanding your ovarian reserve now, even before you start trying is genuinely useful. AMH testing reflects egg quantity relative to your age and can inform decisions about timing and whether egg freezing is worth considering.

For a full breakdown of how age affects fertility and what the data says about conception in your 30s and 40s, see our guide: How ageing affects fertility →

💡 Hertility tip: Hertility’s at-home Advanced Hormone and Fertility Test measures up to 10 key hormones relevant to ovulation and conception including FSH, LH, oestradiol, AMH, prolactin, testosterone, and thyroid function, with a clinician-reviewed report that screens for 18 reproductive health conditions. Results in 6 days, no GP referral needed. If your results flag anything worth investigating further, our clinical team can refer you for an ultrasound scan directly. Start your assessment →

When to seek help if you’re not getting pregnant

Most people expect conception to happen quickly. The reality is that it often takes longer than we think , and that’s not necessarily a sign something is wrong. Around 80–85% of couples under 35 conceive within 12 months.

As a general guide, it’s worth seeking fertility investigations:

• If you’re under 35: after 12 months of regular, unprotected sex without conceiving
• If you’re 35 or over: after 6 months of regular, unprotected sex without conceiving

Regular sex generally means every 2–3 days throughout the cycle, or more focused timing around the fertile window if you are tracking ovulation.

When to Seek Help Sooner

You don’t need to wait 6 or 12 months if there are signs that something else may be going on. It’s worth speaking to a clinician sooner, at any age, if:

• Your cycles are irregular, shorter than 21 days, longer than 35 days, or absent
• You have a known condition such as PCOS, endometriosis, thyroid disease, or premature ovarian insufficiency
• You’ve had previous pelvic surgery, pelvic inflammatory disease, or a significant pelvic infection
• Sex is painful, difficult, or has changed
• You’ve had recurrent miscarriages
• Either partner has a history of chemotherapy, radiotherapy, testicular surgery, undescended testes, or significant hormonal concerns
• You have significant concerns about either partner’s health history
• You simply feel something isn’t right and want clarity earlier

Painful sex is especially important not to dismiss. It can be linked to conditions such as endometriosis, pelvic floor dysfunction, infections, vaginal dryness, or inflammation, some of which may also affect fertility or make trying to conceive emotionally and physically harder.

What do fertility investigations usually involve?

Fertility investigations are designed to understand whether ovulation is happening, whether sperm parameters are within range, whether the uterus and ovaries look healthy, and whether the fallopian tubes are open.

For women, this may include a hormone blood panel looking at markers such as FSH, LH, oestradiol, AMH, prolactin, testosterone, and thyroid function. You may also be offered an ultrasound scan to assess the ovaries, uterus, antral follicle count, fibroids, polyps, ovarian cysts, or signs of conditions such as PCOS or endometriosis. In some cases, a HyCoSy or hysterosalpingogram (HSG) may be recommended to check whether the fallopian tubes are open.

For men, the key first-line test is a semen analysis, which looks at sperm count, motility, and morphology. Male-factor fertility issues contribute to around half of fertility difficulties, yet semen testing is often delayed or treated as an afterthought. If you’re trying to conceive with a male partner, semen analysis should ideally happen in parallel with female investigations, not only after everything else has been checked.

How Hertility can help

Whether you’re just starting your TTC journey or have been trying for a while, Hertility is designed to give you answers, without waiting rooms, long referral queues, or having to push for tests you already know you need.

Hertility’s Advanced At-Home Hormone and Fertility Test is the most comprehensive starting point for anyone trying to conceive. It measures hormones relevant to ovulation and conception — FSH, LH, oestradiol, AMH, testosterone, prolactin, and thyroid function  and screens for 18 reproductive health conditions including PCOS, diminished ovarian reserve, thyroid disorders, and more.

If your hormone results suggest further investigation is warranted, Hertility’s clinical team can refer you directly for a pelvic ultrasound scan. This means you can move through the diagnostic pathway without waiting for an NHS GP referral, getting answers weeks or months sooner.

Every Hertility test comes with access to clinical support. If your results indicate a condition that requires specialist care, our team can advise on next steps and refer you to an appropriate specialist. You don’t have to navigate what your results mean alone.

Frequently asked questions

How often should you have sex to get pregnant? 

Every 2–3 days throughout your cycle is better than just focusing on having sex during  the fertile window. What the research doesn’t support is saving everything up for a single “best day” you want sperm present across the peak days, not just at one point.

Does position affect conception chances? 

No reliable evidence supports this. Sperm enter the cervix rapidly after ejaculation regardless of position. You don’t need to lie still, elevate your hips, or stay in any particular position afterwards.

What’s the difference between an ovulation test and a fertility test? 

An ovulation test (OPK) detects the LH surge that precedes ovulation, it tells you when ovulation is likely in that cycle. A fertility hormone test (like Hertility’s) measures a broader panel of reproductive hormones to assess your overall hormonal health and ovarian reserve and can screen for underlying conditions that might affect your fertility.

I’m 30 and we’ve been trying for 8 months and nothing has happened, should we be worried? 

Not necessarily, but it’s a reasonable point to start gathering information. Getting a hormone test and tracking your cycles accurately will give you and any future clinician a much clearer picture than waiting until the 12-month mark and starting from scratch. If you have any cycle irregularities or symptoms, consider seeking a referral earlier rather than waiting.

References

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