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Fertility basics

Best Time to Get Pregnant: Can You Tell Fact from Fiction?

best time to get pregnant

Knowing the best time to get pregnant doesn’t always mean it’ll happen as soon as you want it to. In fact, in our recent survey of over 2,000 women, we found that 83% underestimated the amount of time it would take to get pregnant, with nearly half not understanding how important timing intercourse was in order to conceive.

The best time to get pregnant comes down to knowing when you ovulate. Your fertile window is the 5 days before ovulation and the day of ovulation itself. Peak fertility occurs during the 2 – 3 days before ovulation.

Can you get pregnant any time of the month?

Despite what you may have learned in high school sex-ed, a woman can’t get pregnant any time during the month. The only time when it’s possible to conceive is during your maximum fertile window, which is the five days before ovulation and the day of ovulation itself (the fertile window may be shorter in some women, but not longer).

However, if you don’t know when ovulation occurs, then it might feel like you could get pregnant any time simply because you don’t know when your fertile window happens. You can use online ovulation calculators to estimate when your fertile window is based on the date of your last menstrual period. You should be aware that this method of calculating your fertile window is imprecise—for more accurate results, you need to use a method that incorporates additional information, such as vaginal discharge observations and LH tests.

How many days after your period are you the most fertile?

This depends on how long your menstrual cycle is. You can get pregnant only during your fertile window, which includes the day of ovulation and the five days leading up to ovulation. If you have a textbook 28-day menstrual cycle with ovulation on day 14, your fertile window would be days 9 – 14 of your menstrual cycle (with a 5-day period, this would mean you are fertile starting from 4 days after your period, and most fertile around days 11 – 13).

But for 70% of women, the fertile window does not fall entirely within this timeframe. Since the fertile window is defined retrospectively based on when you ovulated, if you don’t ovulate on day 14, your fertile window will not end on day 14 or start on day 9.

If you ovulate much later than day 14, your fertile window will start much later after your period ends. And if you ovulate earlier than day 14, you may even be able to get pregnant during your period.

Does the best time to get pregnant change from cycle to cycle?

Yes. For reasons that scientists are still trying to understand, cycle length and fertility can vary from cycle-to-cycle in the same woman. A study from 2006 observed over 100 women for multiple cycles and found that about one-third of the women, the fertile window varied by up to a week from between cycles.

It’s perfectly normal to have your fertile window or ovulation day vary each cycle. But it does mean that to make the most of your fertility calendar, you need to understand your unique cycle. That means tracking your ovulation so you can make the most out of your chances.

Is the best time to get pregnant on ovulation day?

Surprisingly, the day of ovulation itself carries a lower chance of conception than the two to three days leading up to ovulation. A study from 1998 observed conception rates from couples who had intercourse during the fertile window and found that the conception rate was 36 percent two days before ovulation and 34% the day before ovulation. For comparison, intercourse three, four, or five days before ovulation had an 8 – 17 percent chance of conception.

A more recent, and larger, study from 2000 found that the greatest chances of conception came from intercourse that occurred during the three days preceding ovulation.

In the 1998 study, intercourse on day of ovulation had a high conception rate (36%), and it also had the higher rate of chemical pregnancy (a form of early miscarriage). It’s possible that this has to do with how long the egg has been around before sperm fertilize it, but more research is needed to know for sure.

This doesn’t mean that you should avoid having sex on the day of ovulation—the chances of miscarriage were overall very small. But it does mean that you should focus your efforts on having sex on the days leading up to ovulation, rather than trying to pinpoint the precise day of ovulation.

How often should you have sex during the fertile window?

Having sex every day of your fertile window results in a 25 percent chance of conceiving a healthy pregnancy, and the chance slightly drops to 22 percent if you have sex every other day.

But how often you should have sex to get pregnant depends on the quality of your partner’s sperm. If sperm counts are average (at least 20 million per milliliter of sample), then having sex everyday increases the chances of fertilization. If his counts are lower, then intercourse every other day can increase odds of fertilization because it gives time for more sperm to be available per ejaculation. If his counts are high, have intercourse as much as you want!

Should you have sex after ovulation?

No! This is one of main problems with using basal body temperature to track ovulation: the most obvious thing to look for (aka the rise in body temperature) happens after ovulation and when the fertile window closes. So, before ovulation, basal body temperature is lower, and after ovulation, body temperature increases. This shift in temperature around ovulation is called a biphasic pattern, so if you see this pattern, it’s likely that ovulation occurred (but the only way to definitely confirm ovulation is via ultrasound).

The bottom line? If you’re really diligent about this method, then you could use information from previous cycles’ body temperature to predict ovulation yourself. BUT, remember the point above that you can ovulate on different days each cycle, so one major drawback is that you might not always get the most accurate information.

Does fertility drop after age 35?

Not as much as you might think. Many women fear age 35 as the dreaded fertility cliff, scared that chances of conceiving drop dramatically after this point. But, where does the number 35 even come from in this issue? Turns out that it comes from a study that found that changes of conceiving drop from 75% to 66% from age 30 to 35 for women in the 1600s. That’s right: the study used women from four hundred years ago, scaring women about age 35 since then.

A study of women from a more recent century (1990s) found that for women between 27 – 29 years old, probability of conception was about 80% within a year of trying to conceive. For women in the 35 – 39 years old group, the probability was about 77%. That’s just a 3% difference!

Should you wait three months to try again after a miscarriage?

No: you can go ahead and try getting pregnant after miscarriage as soon as you feel ready. In fact, women who conceive again within the first six months after a miscarriage are less likely to have a subsequent miscarriage.

Note that it can take some time for hCG levels to fall after miscarriage, which is necessary in order for ovulation to resume.

The good news is that if you’ve experienced a miscarriage, the likelihood of experiencing another one doesn’t increase. If you experience recurrent miscarriage (meaning two or more consecutive miscarriages), then talk to your doctor about causes of miscarriage and what your options are.


View sources

Can assisted reproduction technology compensate for the natural decline in fertility with age? A model assessment

Increased Infertility With Age in Men and Women

Effect of interpregnancy interval on outcomes of pregnancy after miscarriage: retrospective analysis of hospital episode statistics in Scotland

Variability in the phases of the menstrual cycle.

Daily fecundability: first results from a new data base.

Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby

Post-ovulatory ageing of the human oocyte and embryo failure.

Aarthi Gobinath, PhD

Aarthi Gobinath earned her PhD in neuroscience from the University of British Columbia. Her research covers the ways that stress affects the male and female brain differently.

She tackled the issue of sex bias in research by looking at why standard treatments for depression don't always work in the case of postpartum depression. Her work has been covered by Vice and Massive Science.

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