The best time to get pregnant is during the five days before ovulation and the day of ovulation itself. This six-day stretch is called the fertile window, and your chances peak about two days before the egg is released, when the probability of conception reaches roughly 26% per cycle. By contrast, having sex even one day after ovulation drops that probability to around 1%.
Why the Fertile Window Works
The math behind the fertile window comes down to two biological clocks running on very different timescales. Sperm can survive inside the uterus and fallopian tubes for three to five days, while a released egg lives for less than 24 hours. That mismatch means sperm need to already be waiting when the egg arrives. Sex in the days leading up to ovulation positions sperm in the fallopian tubes ahead of time, which is why the highest conception rates happen before ovulation rather than on the day itself.
Once that narrow egg-survival window closes, conception for that cycle is essentially off the table. This is why timing matters more than almost any other single factor when you’re trying to conceive.
How Often to Have Sex
During the fertile window, having sex every one to two days gives you the best odds. A large review by the American Society for Reproductive Medicine found that daily and every-other-day intercourse produced similar conception rates, so there’s no advantage to a rigid daily schedule if that feels like pressure. The only notable drop-off came when couples had sex just once during the entire fertile window.
One persistent myth is that “saving up” sperm by abstaining improves quality or count enough to matter. It doesn’t. More frequent sex does not lower your chances, and couples trying to conceive shouldn’t limit how often they have sex based on that idea.
How to Pinpoint Ovulation
Since the fertile window revolves around ovulation, tracking when it happens is the most useful thing you can do. There are three practical approaches, and combining them gives you the clearest picture.
Cervical Mucus
Your body produces a specific type of mucus as ovulation approaches. In the days leading up to the egg’s release, mucus becomes clear, slippery, and stretchy, often compared to raw egg whites. This “fertile-type” mucus isn’t just a signal; it’s functionally necessary. Sperm can’t survive or travel to the egg without it. On days with no noticeable mucus, the probability of conception is nearly zero (about 0.3%). On days with the most fertile-type mucus, it jumps to close to 30%. Tracking mucus changes gives you a real-time, forward-looking indicator that ovulation is coming soon.
Ovulation Predictor Kits
These urine-based tests detect a surge in luteinizing hormone (LH), the chemical trigger that causes the ovary to release an egg. Ovulation typically happens 36 to 40 hours after the LH surge begins, so a positive test tells you you’re about a day and a half away. That makes the day of the positive test and the following two days your highest-priority window for sex.
Basal Body Temperature
Your resting temperature rises slightly after ovulation, typically by less than half a degree Fahrenheit (the exact shift varies from person to person, ranging from about 0.4°F to 1°F). The catch is that the temperature rise confirms ovulation has already happened, so it’s a backward-looking tool. It won’t tell you when to have sex this cycle, but tracking it over several months reveals your personal pattern, helping you predict the timing of future cycles.
Using cervical mucus or an ovulation kit to look ahead, then confirming with temperature afterward, gives you both the planning advantage and the confirmation that your body is ovulating consistently.
How Age Affects Your Odds
Even with perfect timing, the per-cycle probability of conception changes significantly with age. A woman in her early to mid-20s has a 25 to 30% chance of getting pregnant each month. That rate holds relatively steady through the late 20s, then begins a gradual decline through the 30s. By age 40, the chance of conceiving in any given cycle drops to around 5%.
This decline reflects changes in both egg quantity and egg quality over time. It doesn’t mean pregnancy at 40 is impossible, but it does mean that fewer cycles will result in conception, and the process often takes longer. If you’re over 35 and haven’t conceived after six months of well-timed sex, that’s generally the point where fertility evaluation becomes worthwhile. For those under 35, the typical benchmark is 12 months.
What to Do Before You Start Trying
Timing sex correctly is the biggest lever you can pull, but a few preconception steps improve both your chances and the health of a future pregnancy. The most evidence-backed one is folic acid. The CDC recommends 400 micrograms daily for all women who could become pregnant, ideally starting at least one month before conception. Folic acid dramatically reduces the risk of neural tube defects, which form in the earliest weeks of pregnancy, often before you even know you’re pregnant. If you’ve had a previous pregnancy affected by a neural tube defect, the recommended dose increases to 4,000 micrograms daily.
Beyond supplementation, the basics matter: maintaining a stable weight, managing chronic conditions like thyroid disorders or diabetes, and reducing alcohol intake all support both fertility and early fetal development. These aren’t factors that override timing, but they create the healthiest possible environment once conception happens.
Putting It All Together
The practical strategy is straightforward. Start tracking cervical mucus daily so you recognize the shift to clear, stretchy, fertile-type secretions. Use an ovulation predictor kit around the time you expect the shift, typically mid-cycle. Once you see fertile mucus or a positive LH test, have sex every one to two days for the next few days. Confirm ovulation with a temperature rise, and use that data to refine your timing in future cycles.
Most couples who time intercourse well conceive within six months. If you’ve been tracking carefully and hitting the fertile window consistently without success, that timeline gives you a reasonable benchmark for deciding when to seek further evaluation.