Fertility by Age Calculator

Fertility here means fecundability, the chance of getting pregnant in one menstrual cycle. It is highest in a woman's 20s and early 30s and falls with age, faster after the mid 30s. The calculator starts from the average chance for your age group in a large study, then adjusts it for how long you have been trying.

What Fertility by Age Measures

The result is the average chance for women your age in couples with no known fertility problems. It is not a test of your own fertility, and it cannot tell whether you ovulate or how healthy your partner's sperm is. It estimates the chance of pregnancy, not of a live birth.

The Formula

Starting chance per cycle = 22.3% x age factor

Chance in a later cycle = starting chance x 6.75 / (6.75 + months already tried)

Chance within 6 or 12 cycles = 1 minus the chance of not getting pregnant in any of those cycles

The age factors come from PRESTO, a North American study that followed 2,962 couples trying to conceive for up to 12 cycles¹. The two constants, 22.3% and 6.75, were set so the formula matches that study's results: 79% of women aged 25 to 27 were pregnant within 12 cycles, and 62% of women aged 28 to 30 within 6 cycles¹.

How This Calculator Computes Your Result

Enter your age (18 to 55) and the months you have been trying (0 to 36). Your male partner's age is optional and adds a note only. The tool finds your age group, works out your chance in each of the next 12 cycles, and multiplies the chances of not conceiving to get your 6 and 12 month results. One month counts as one cycle, and results are rounded to whole percentages. To find your fertile days, use the Ovulation Calculator.

What Your Result Means

These are the starting chances for couples who are just beginning to try (0 months tried).

The age factor compares each group with women aged 21 to 24. Chances stay close together into the mid 30s, and the larger drops come at 37 and at 40¹. This fits the ACOG and ASRM view that fertility falls gradually but significantly from about age 32, and more quickly after 37². ASRM also notes that fertility at 40 is about half that of women in their late 20s and early 30s³. Ages 18 to 20 use the 21 to 24 row. Ages 46 and over get no percentage, because the studies stop at 45.

Why Your Monthly Chance Falls the Longer You Try

Couples differ in fertility. Those with the highest chances tend to conceive early, so couples still trying have lower chances on average. ASRM states that the chance of pregnancy per month is greatest in the first 3 months³. So this calculator lowers your chance for each month already tried.

A common mistake is to use the same chance every month. At 20% per cycle, that shortcut predicts 93% pregnant within a year, but in PRESTO only 79% of women aged 25 to 27 were¹. A slow start is not the end of the road. In a European study of 782 couples, an estimated 43% to 63% of couples who had not conceived after 12 cycles did so in the next 12, depending on age⁴. Only about 1% of couples were sterile (unable to conceive at all without treatment), and this did not change with age⁴.

When to Talk to a Doctor About Fertility

ASRM advises a fertility evaluation after 12 months of trying when the woman is under 35, and after 6 months when she is 35 or older⁵. This applies to couples having regular sex without birth control and no known cause of fertility problems⁵. For women older than 40, ACOG and ASRM say an evaluation is warranted right away². Your result shows where you are on this timeline. Irregular or absent periods, or a known condition in either partner, are reasons to see a doctor sooner.

Does a Partner's Age Matter?

The evidence is mixed. The European study found male age began to matter in the late 30s, with couples not conceiving within 12 cycles rising from about 18% to 28% between ages 35 and 40⁴. PRESTO found little link once the woman's age was counted¹, and ASRM states male fertility does not seem much affected before about 50³. So this calculator notes your partner's age but does not change your numbers.