| "Helping women track their ovulation in a smarter way" | 
The menstrual cycle has four phases – menstruation, follicular, ovulation, and luteal. You can only get pregnant in the days around ovulation, a 6-day fertile window ending on ovulation day itself. In a 28-day cycle, this falls roughly between days 10 and 15. Peak fertility is the day before ovulation and the day of ovulation, with pregnancy chances of approximately 25–30% per cycle for a healthy couple (ACOG, 2023).
It’s easy to assume everyone ovulates on day 14, but that’s rarely the case. Your ovulation day depends on your unique cycle length, so your most fertile days may come earlier or later than expected. Tracking your LH surge helps identify your actual fertile window instead of relying on calendar estimates.
Key takeaways
- The menstrual cycle has four phases: menstruation (days 1–5), follicular phase (days 1–13), ovulation (day 14 in a 28-day cycle), and luteal phase (days 15–28).
- You can only get pregnant during the fertile window, approximately 6 days ending on ovulation day. Outside this window, pregnancy is biologically impossible.
- The highest pregnancy chance is the day before ovulation and the day of ovulation. Sex on these two days gives the best conception odds.
- Can you get pregnant on your period? Technically yes, for women with short cycles (21–25 days), sperm can survive long enough to reach an early ovulation.
- Premom’s LH surge detection identifies your ovulation window 24–36 hours in advance, removing the guesswork for any cycle length.
The four menstrual cycle phases explained
The menstrual cycle is a hormonal loop designed to prepare the body for pregnancy every month. It begins on day 1 of your period and ends the day before your next period starts. Every person’s cycle length varies, while 28 days is the commonly cited average, anything between 21 and 35 days is considered within normal range.
Use this table as a cycle-at-a-glance reference before reading the full explanation of each phase:
| Phase | Typical days (28-day cycle) | Key hormone | Fertility status |
|---|---|---|---|
| Menstruation | Days 1–5 | Progesterone has dropped | Very low, possible only in very short cycles |
| Follicular | Days 1–13 | FSH briefly, then rising estrogen | Low rising to high near ovulation |
| Ovulation | ~Day 14 | LH surge | Peak, highest pregnancy chances |
| Luteal | Days 15–28 | Progesterone | Drops to near zero by day +1 post-ovulation |
Menstruation phase: days 1–5
The menstrual phase begins on cycle day 1, the first day of full-flow bleeding. It occurs because the previous cycle didn’t result in pregnancy: progesterone drops, and the uterine lining (endometrium) sheds.
Conception is highly unlikely during menstruation because hormone levels are low and the lining is shedding. For most people, pregnancy is effectively impossible during their period. The exception is women with very short cycles, more on this below.
Follicular phase: days 1–13
The follicular phase begins on day 1 alongside menstruation and lasts until ovulation. It’s typically the longest and most variable phase of the cycle, and the reason cycle lengths differ between people.
FSH prompts several ovarian follicles to grow. One dominant follicle is selected, and as it matures, it releases rising amounts of estrogen. That estrogen thickens the uterine lining and transforms cervical mucus from dry and sticky to clear, stretchy, and egg-white in texture. This change in cervical mucus is both a fertility signal and a physical environment that supports sperm survival and travel.
Pregnancy chances begin rising in the late follicular phase as cervical mucus becomes fertile and the body approaches the ovulation window. Logging cervical mucus, symptoms, and LH tests together in Premom helps you see how these fertility signs change as you move through the follicular phase and approach ovulation.
Ovulation phase: when does ovulation happen?
Ovulation is triggered by a sharp surge in LH. The LH surge forces the dominant follicle to rupture and release the mature egg into the fallopian tube. The egg survives only 12–24 hours, so the timing of intercourse relative to egg release is critical.
Ovulation happens on different days for different people:
- 21-day cycle → ovulation around day 7
- 28-day cycle → ovulation around day 14
- 35-day cycle → ovulation around day 21
Because the luteal phase is relatively fixed at 12–16 days, ovulation day is calculated by subtracting 14 from your total cycle length, but this is still an estimate. LH testing tells you when the surge is actually happening, not when it’s predicted to happen.
Luteal phase: days 15–28
The luteal phase begins immediately after ovulation and lasts until the day before your next period, typically 11–17 days. The ruptured follicle transforms into the corpus luteum, which produces progesterone. Progesterone thickens and maintains the uterine lining in case an embryo needs to implant.
After ovulation, adding BBT or PdG results alongside your LH data provides a more complete picture of the luteal phase and helps you review how your cycles compare over time.
If fertilization doesn’t occur, the corpus luteum breaks down, progesterone falls, and menstruation begins. Once the egg has passed its 24-hour viability window, the chance of conception in that cycle drops to near zero. The luteal phase is preparation and waiting, not conception.
A luteal phase shorter than 10 days (called a short luteal phase) may not provide enough progesterone to support implantation and is worth discussing with your provider.
Key terms explained
Menstrual cycle: The recurring hormonal process that prepares the body for pregnancy. It begins on day 1 of your period and ends the day before your next period starts. Normal length: 21–35 days.
Follicle-Stimulating Hormone (FSH): Released by the brain to stimulate follicle growth in the ovaries. Rising FSH in the early cycle triggers the development of a dominant follicle.
Luteinizing Hormone (LH): The hormone that surges 24–36 hours before ovulation, triggering egg release. Detected by ovulation predictor kits (OPKs).
Fertile window: The approximately 6-day window each cycle when conception is possible, the 5 days before ovulation plus ovulation day itself.
Corpus luteum: The structure formed from the follicle after it releases the egg. It produces progesterone to support a potential pregnancy during the luteal phase.
PdG (Pregnanediol Glucuronide): The urine metabolite of progesterone. A positive PdG test in the luteal phase provides evidence that ovulation occurred and progesterone levels are sufficient.
What are the chances of getting pregnant at each stage of the cycle?
Pregnancy chance isn’t distributed evenly across the cycle, it clusters tightly around ovulation and falls off sharply before and after.
Chances of getting pregnant each day of the cycle
| Day relative to ovulation | Approximate pregnancy chance |
|---|---|
| Day −5 | 4% |
| Day −4 | 8% |
| Day −3 | 15% |
| Day −2 | 25% |
| Day −1 (day before ovulation) | ~30% |
| Day 0 (ovulation day) | ~25–30% |
| Day +1 (day after ovulation) | ~1% |
| Day +2 and beyond | Under 1% |
What day gives you the highest chance of getting pregnant?
The day before ovulation and the day of ovulation, both carrying roughly 25–30% chance of conception per cycle for a healthy, fertile couple. The slight edge to the day before ovulation reflects that having sperm already present in the fallopian tube when the egg arrives gives it more time for fertilization.
What are the 6 days you can get pregnant?
The 6-day fertile window consists of the 5 days before ovulation plus ovulation day itself. This window exists because sperm can survive up to 5 days in fertile cervical mucus. Sex any day within this window can result in pregnancy, with chances rising progressively toward the end of the window.
What day of the cycle is the lowest chance of pregnancy?
The days immediately following ovulation, day +1 onward into the luteal phase, carry the lowest pregnancy chance (under 1%). The egg has expired and the luteal phase progesterone environment doesn’t support a new ovulation. The very beginning of a cycle (days 1–3 of the period) is also very low probability for most people, though slightly higher than mid-luteal phase for women with short cycles.
When is a woman most fertile? The fertile window
The fertile window is the approximately 6-day period ending on ovulation day when conception is biologically possible. It shifts based on your actual ovulation timing, not a calendar formula.
When are you most fertile?
You are most fertile in the 1–2 days surrounding ovulation — specifically the day before and the day of ovulation. These two days account for the highest probability of conception. The 3–4 days before these peak days also carry meaningful fertility chances due to sperm survival.
How many days after a period am I most fertile?
| Cycle Length | Fertile Window Start | Additional Details |
|---|---|---|
| 24-day cycle | Around Day 8–9 | Approx. 3–4 days after a 5-day period |
| 28-day cycle | Around Day 9–10 | Standard / typical timing |
| 35-day cycle | Around Day 16–17 | Delayed onset due to longer cycle |
These are estimates. The only way to know precisely is to track your actual LH surge. Using ovulation test strips from cycle day 8 onward ensures you don’t miss an earlier-than-expected surge.
Best time to get pregnant after your period
The best time to try to conceive after your period is in the final days of your follicular phase, as your LH is beginning to rise and cervical mucus is becoming egg-white in texture. Starting to have sex every 1–2 days once you see fertile mucus or the beginning of an LH rise gives you the best coverage of the full fertile window.
Are you fertile after your period?
Yes, in most cycles, your fertility rises steadily from the end of your period through the follicular phase and peaks around ovulation. You are not fertile in the first days of your period (unless you have a very short cycle), but fertility builds as you move through the follicular phase.
What are signs you’re very fertile?
Indicators of peak fertility in a given cycle:
- Egg-white cervical mucus — clear, stretchy, slippery
- A clear LH surge on ovulation test strips
- Mild one-sided pelvic pain (mittelschmerz) around ovulation
- Slight increase in basal body temperature by 0.2–0.5°F after ovulation (suggesting ovulation likely occurred)
- Increased libido around mid-cycle
How do I know if I’m fertile enough to get pregnant?
The most accessible starting points:
- Track your LH surge across 2–3 cycles, are you getting a consistent peak? Premom’s LH reading quantifies your surge numerically.
- Track your BBT — a consistent temperature rise after ovulation suggests ovulation has occurred.
- Assess cycle regularity — cycles consistently between 21–35 days with a clear period suggest regular ovulation.
If you’ve been trying for 12 months (or 6 months if over 35) without success, a provider evaluation is the appropriate next step.
When does ovulation start and how long does it last?
Ovulation itself is a brief event, the actual release of the egg takes only a few minutes. But the fertile window around it spans about 6 days due to sperm survival.
How long does ovulation last?
The egg is viable for only 12–24 hours after release. This is the narrow window during which fertilization must occur. The egg doesn’t “last” for the full fertile window, sperm do. Because sperm can survive for several days in fertile cervical mucus, having sperm present before the egg is released is the key strategic advantage.
When do I ovulate?
You ovulate approximately 24–36 hours after your LH surge peaks. Since LH strips detect the surge as it rises, a positive LH test typically means ovulation will occur within 1–2 days. The exact day varies:
- Short cycles (21 days): Around day 7
- Average cycles (28 days): Around day 14
- Longer cycles (35 days): Around day 21
Will I 100% get pregnant if I’m ovulating?
No. Even with perfectly timed intercourse during the fertile window, healthy couples have roughly a 25–30% chance of conception per cycle. Multiple factors affect whether fertilization and implantation succeed, sperm quality, egg quality, uterine environment, and chance. Most couples trying to conceive naturally take several months. The data shows a cumulative pregnancy rate of 82% after 12 menstrual cycles.
Can you get pregnant on your period?
Technically yes, though the chance is very low for most people.
Are you fertile on your period?
For most women with average or long cycles, the answer is no, ovulation is too far away for sperm to survive until egg release. But for women with shorter cycles (21–25 days), the math changes. If your period lasts 5 days and you ovulate on day 7 or 8, having sex on day 5 of your period means sperm could still be viable when the egg is released.
Can I get pregnant 3 days after my period?
Yes, particularly if you have a shorter-than-average cycle. If your period ends on day 5 and ovulation occurs around day 8 or 9 (possible in a 21–23 day cycle), day 8 is within the fertile window. The likelihood depends on your specific cycle length and ovulation timing.
How many days after your period can you get pregnant?
This depends entirely on your ovulation timing. In a 28-day cycle, your fertile window begins approximately 9 days after your period starts (if your period lasts 5 days, that’s 4 days after it ends). In a shorter cycle, your fertile window can begin immediately after your period ends. There’s no universal answer, your individual LH pattern is the only reliable guide.
What happens two days before your period?
Two days before your period, you’re in the late luteal phase. The corpus luteum is breaking down, progesterone is falling, and the uterine lining is preparing to shed. Pregnancy is not possible at this point in the cycle. Any egg from the current cycle is long gone. This is also the phase when PMS symptoms — bloating, mood changes, breast tenderness — are most common, driven by the drop in progesterone.
Can you get pregnant right after your period?
Yes, this is one of the most important things to understand about cycle-based fertility planning.
Can you get pregnant 2 days before your period?
Very unlikely. Two days before your period, you’re deep in the luteal phase, the egg from the current cycle is long expired, and no new ovulation will occur before menstruation begins. However, if you have a very irregular cycle and what you think is “2 days before your period” turns out to be a longer-than-usual follicular phase, there is theoretical uncertainty, which is why tracking is more reliable than guessing based on calendar dates.
Can you get pregnant 5 days before your period?
Still very unlikely, but less certain than 2 days before. Five days before a 28-day period is day 23, which is well into the luteal phase. The risk increases if your cycle is irregular and you’ve miscalculated where you actually are relative to ovulation. If your cycles vary significantly month to month, calendar-based predictions don’t provide reliable protection against unintended pregnancy.
Could you get pregnant right before your period?
In a regular cycle, no, right before your period is the end of the luteal phase, the furthest point from ovulation. In an irregular cycle where ovulation timing is unpredictable, there’s more uncertainty. This is why tracking your actual LH surge rather than estimating from a calendar provides clearer information about where you are in your cycle.
When is the lowest chance to be pregnant?
The lowest conception chance occurs in the mid-to-late luteal phase, approximately days 18–26 in a 28-day cycle. By this point, the current cycle’s egg has expired and the hormonal environment actively prevents new ovulation from occurring before menstruation resets the cycle.
Can you get pregnant when you’re not ovulating?
No. Pregnancy requires fertilization of an egg. Without ovulation, there is no egg to fertilize, and conception is impossible in that cycle.
Can you only get pregnant during ovulation?
Fertilization can only occur within 24 to 48 hours after the egg is released. However, because sperm can survive for several days in fertile cervical mucus, sex in the 5 days before ovulation can also result in pregnancy, making the fertile window 6 days rather than just 1. So while the biological act of fertilization requires a live egg, conception results from sex that occurred during the broader fertile window.
Can you get pregnant 3 days after ovulation?
No. By 3 days after ovulation, the egg has expired and the opportunity for fertilization in that cycle has passed. What women sometimes experience 3 days after ovulation is the very beginning of early progesterone-driven changes, which can feel similar to early pregnancy symptoms, but pregnancy at this point can’t be confirmed until hCG becomes detectable approximately 10–14 days past ovulation.
Can 2-day-old sperm fertilize an egg?
Yes. Sperm can remain viable in fertile cervical mucus for up to 5 days, and some sperm retain fertilization capacity for 2–3 days. Two-day-old sperm deposited in fertile cervical mucus before ovulation can absolutely fertilize an egg. This is why having sex in the days leading up to ovulation, not just on the day, is part of an effective conception strategy.
How to conceive faster: getting pregnant at the right cycle phase
Timing intercourse strategically within your fertile window is the most effective thing most couples can do to improve their monthly conception chances.
How long does it take to conceive?
For healthy couples having timed, regular intercourse:
- Approximately 30% conceive in the first month
- Approximately 75% conceive within 6 months
- Approximately 85–90% conceive within 12 months
After 12 months of trying (or 6 months if you’re over 35), a fertility evaluation is recommended by ACOG.
At what age are 90% of your eggs gone?
Research suggests that by age 30, a woman has lost approximately 90% of her egg supply, though this reflects quantity, not quality. Egg quality also declines with age, which is why fertility rates drop more significantly from the mid-30s onward. This is why age over 35 triggers earlier fertility evaluation guidelines; the window to act on findings is shorter.
How to get pregnant faster with Premom ovulation tracking
Knowing when your fertile window begins can make it easier to time intercourse during the days leading up to ovulation. When used together, the easy@Home ovulation test kit and Premom app help you track your LH trend over time, while your period history, symptoms, and fertility chart provide additional context for understanding your cycle.
After ovulation, you can also log your BBT to look for a sustained temperature shift and compare your cycle patterns across multiple months. Seeing these fertility signs together can provide a more complete picture of your cycle than relying on a calendar alone.
Factors that shift your cycle phases
Your cycle phases aren’t fixed, the hormonal system that runs them is sensitive to internal and external stress.
| Factor | Effect on cycle |
|---|---|
| High stress or illness | Delays LH surge, lengthens follicular phase |
| Significant weight change | Alters estrogen, may delay or prevent ovulation |
| PCOS | Prolonged or inconsistent follicular phase, unpredictable ovulation |
| Coming off hormonal contraception | Variable cycle lengths while HPO axis recalibrates |
| Perimenopause (late 30s–40s) | Shorter follicular phase or anovulatory cycles |
| Travel and disrupted sleep | Can delay LH surge by days |
Looking back at several cycles in Premom can help you recognize whether a delayed ovulation or longer follicular phase is an isolated event or part of a recurring pattern worth discussing with your healthcare provider.
Common cycle irregularities that affect your fertile window
- Anovulatory cycle: The follicular phase occurs, but no LH surge is strong enough to trigger egg release. A period (or withdrawal bleed) still occurs, but there is no luteal phase and no chance of pregnancy in that cycle.
- Short luteal phase: Consistently fewer than 10 days between ovulation and your period — the body may not produce enough progesterone for long enough to support implantation.
- Long or inconsistent follicular phase: Common with PCOS, ovulation timing is highly unpredictable, making calendar-based fertile window estimates unreliable.
- Spotting or skipped periods: May indicate hormonal imbalance worth investigating with a provider.
Frequently asked questions about menstrual cycle phases and fertility
Pregnancy is only possible during the fertile window, the 6 days ending on ovulation day. Chance peaks at approximately 25–30% on the day before ovulation and ovulation day itself. After ovulation, the chance falls to under 1% by day 1 DPO and to essentially zero by day 2 and beyond.
The day before ovulation and ovulation day itself, both carrying approximately 25–30% conception chance per cycle for a healthy couple. The day before ovulation holds a slight advantage in some studies because sperm are already present when the egg is released. Having sex on both days gives the best coverage.
The 6-day fertile window consists of the 5 days before ovulation and ovulation day. Sperm survive up to 5 days in fertile cervical mucus, making any day in this window a potential conception day, with chances rising progressively toward the final 2 days.
Yes, if you have a short cycle. In a 21–23 day cycle, ovulation can occur as early as day 7–9. If your period lasts 5 days, you could be 3 days out from your period and still within or approaching your fertile window. The only way to know for certain is to track your LH surge rather than count days from your period.
Very unlikely for most women. Two days before your period is the late luteal phase, the egg from the current cycle has long expired. The exception is women with very irregular cycles who can’t reliably predict where they are relative to ovulation. Calendar-based estimates don’t provide certainty; LH tracking does.
No. Even with perfectly timed intercourse, healthy couples have approximately a 25–30% chance per cycle. Multiple biological factors determine whether fertilization and implantation succeed. Most couples conceive within 6–12 months of regular timed intercourse, not in a single cycle.
Start using ovulation tests soon after your period ends so you don’t miss an early LH surge. Have sex every 1–2 days throughout your fertile window, especially around your LH surge. You can also log your BBT after ovulation and compare your cycle patterns over time in the Premom app to better understand your fertile timing.
Yes. Sperm can survive up to 5 days in fertile cervical mucus, so 2-day-old sperm retain fertilization capacity. This is why having sex in the days before ovulation, not just on the day, is effective. Sperm waiting in the fallopian tube when the egg arrives have an equal or better chance of fertilization than sperm deposited on ovulation day itself.
Research suggests approximately age 30, though this figure reflects egg quantity rather than quality. Quality decline becomes more significant from the mid-30s. This underlies why ACOG recommends fertility evaluation after 6 months of trying for women over 35, rather than waiting 12 months.
Peak fertility signs include: egg-white cervical mucus (clear, stretchy, slippery), a clear LH surge on an ovulation test, mild one-sided pelvic pain around ovulation (mittelschmerz), and a subtle BBT rise after ovulation, which suggests that an egg was likely released. Regular cycles of 25–35 days with consistent LH peaks are the strongest ongoing indicators of regular ovulation and a healthy reproductive pattern.
In a 28-day cycle, your fertile window typically begins 4–5 days after a 5-day period ends. In shorter cycles (21–24 days), the fertile window can start immediately after the period ends or even overlap with the last days of it. In longer cycles (35 days), the wait between period end and fertile window is longer. Tracking your actual LH surge helps to remove the guesswork, it tells you where your window is in your specific cycle, not where it statistically “should” be.
The Premom app tracks your LH curve across cycles rather than relying on a fixed cycle-length formula. For women with PCOS, irregular cycles, or variable follicular phases, this means Premom adapts to your actual data rather than applying a 28-day template. You test daily with easy@Home strips, Premom reads and plots your LH trend, and identifies your surge pattern regardless of whether ovulation arrives on day 12 or day 30. Premom’s PCOS Pro feature provides additional support for women whose surge patterns are harder to interpret.
