Fertility by Age Calculator (chance of getting pregnant by age)

Understanding the fertility by age calculator — concept and principle

This calculator shows published estimates of how likely a woman is to become pregnant, and to have a live birth, depending on her age when she starts trying. It also tells you when, by age, it is usually advised to see a doctor if pregnancy has not happened.

Age 32, trying 4 months: with the default inputs the result is 12 months (see a doctor if not pregnant after).

How it is calculated

Two separate studies are used, each only for the ages it covers.

Chance of pregnancy within 12 cycles (Dunson, Baird and Colombo, 2004): about 92% for women aged 19–26, 86.5% at 27–34 and 82% at 35–39.
Live birth within 1 and 4 years (Leridon's 2004 model): 75% and 91% when starting at 30, 66% and 84% at 35, 44% and 64% at 40. Ages in between are interpolated in a straight line; outside 30–40 the page shows "—".
When to see a doctor (ACOG): after 12 months of trying under 35, after 6 months at 35–40, right away over 40.

The principle

Fertility falls with age mainly because the number and quality of eggs decline, which raises the share of cycles that cannot lead to a viable pregnancy. Dunson's study followed 782 European couples who timed intercourse with natural family planning, so it reflects couples trying actively. Leridon's model combines data on monthly conception chance, miscarriage and sterility by age to estimate how many women starting at a given age would have a live birth within a set time.

Worked example

Default inputs: age 32, trying for 4 months.

Age 32 is in the 27–34 band → chance of pregnancy within 12 cycles 86.5%.
Live birth within 1 year: 75 + (66 − 75) × (32 − 30) ÷ 5 = 71.4 → 71%.
Live birth within 4 years: 91 + (84 − 91) × 2 ÷ 5 = 88.2 → 88%.
Under 35 → see a doctor after 12 months of trying; 4 months is less, so Not yet by age guidance.

How to read the result

The figures are averages for groups of women. A high percentage still means some couples take longer, and many conceive in the second year. The male partner's age and health, cycle regularity, previous pelvic infection, endometriosis and other conditions all change the individual chance, so seek advice earlier if any apply.

Common mistakes

Reading the percentage as a personal guarantee.
Waiting the full time despite known problems such as irregular or absent periods.

Keep in mind: This is general information, not a diagnosis or medical advice. Talk to a doctor about your own situation, especially if you have symptoms or a known condition.

Frequently asked questions

At what age does fertility start to decline?

Studies show a gradual decline from the late twenties or early thirties, becoming faster after about 35.

Why see a doctor sooner after 35?

Because the chance per month is lower and time matters more, ACOG advises an evaluation after 6 months of trying.

Sources: Dunson DB, Baird DD, Colombo B, "Increased infertility with age in men and women", Obstet Gynecol 2004;103(1):51–56 · Leridon H, "Can assisted reproduction technology compensate for the natural decline in fertility with age? A model assessment", Hum Reprod 2004;19(7):1548–1553 · ACOG Committee Opinion No. 781, "Infertility Workup for the Women's Health Specialist" (2019)

Checked 9 Nov 2026. Dunson DB, Baird DD, Colombo B, “Increased infertility with age in men and women”, Obstet Gynecol 2004;103(1):51–56; Leridon H, “Can assisted reproduction technology compensate for the natural decline in fertility with age? A model assessment”, Hum Reprod 2004;19(7):1548–1553; ACOG Committee Opinion No. 781, “Infertility Workup for the Women’s Health Specialist” (2019).

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