Evidence Library · The basics

What a normal month actually looks like

Most couples do not conceive in the first month, and that is the ordinary result.

Conception is not likely in any one month, even for couples with nothing wrong. That is normal, and it is the single most useful thing to know before you start counting.

33%

Chance of conceiving from intercourse on the day of ovulation

Highest single day measured

10%

Chance from intercourse five days before ovulation

The other end of the fertile window

80%

Of couples conceive within the first six months of trying

Fertility society figure

Those daily figures come from 221 women who collected a urine sample every morning so that the day of ovulation could be worked out precisely. Even with perfect timing, most single months end without a pregnancy.

The chance also falls with age, but less steeply than most people expect. In 782 European couples keeping daily records, the day-specific chance of conceiving was about twice as high at ages 19 to 26 as at ages 35 to 39. Notice what that does not say: it does not say the older group had no chance, and it does not say their fertile window was shorter. The same study found no evidence that the window gets shorter with age in either partner.

What this means for youIf you have been trying for three months without success, nothing has gone wrong. You have had roughly three chances, each of which was more likely to fail than to succeed. The published advice is to seek evaluation at twelve months under 35, or six months at 35 and over, and that timing exists because most couples who look worried at three months are not.

Where this comes from:

3. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med. 1995;333(23):1517-1521.

2. Dunson DB, Colombo B, Baird DD. Changes with age in the level and duration of fertility in the menstrual cycle. Hum Reprod. 2002;17(5):1399-1403.

8. Practice Committee of the American Society for Reproductive Medicine; Practice Committee of the Society for Assisted Reproductive Technology. Optimizing natural fertility: a committee opinion. Fertil Steril. 2022;117(1):53-63.

1. Dunson DB, Baird DD, Colombo B. Increased infertility with age in men and women. Obstet Gynecol. 2004;103(1):51-56.

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This page is educational. It supports the conversation with your own clinicians. It is not consent to any treatment, and it cannot assess you. If you are worried about a symptom now, see urgent warning signs.