Fertility by Age Calculator

Estimate your average per-cycle chance of natural conception and your cumulative probability of conceiving within a chosen number of months, based on published age-related fertility decline data.

Quick Facts

Per-cycle fecundability
~25% at age 20-24 down to ~5% by age 40-42
Average chance of conception per menstrual cycle with regular unprotected intercourse, based on published age-related fertility data.
Cumulative probability formula
P = 1 - (1 - p)ⁿ
p = monthly fecundability for the entered age; n = number of monthly cycles trying.
ACOG evaluation guidance
12 months (under 35) / 6 months (35+)
Recommended point to seek a fertility evaluation after regular unprotected intercourse without conception.

Your Results

Calculated
Per-cycle fecundability
-
Average chance of conceiving in one cycle at this age
Chance within projected months
-
Cumulative chance across the additional months entered
Chance within 12 months
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Cumulative chance across a full year of trying, from today
Guidance
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Based on ACOG age-based evaluation guidance

Ready

Enter your age and how long you've been trying, then press Calculate.

How Age Affects Fertility

Fecundability — the average chance of conceiving in a single menstrual cycle with regular, unprotected intercourse — declines gradually with age. This decline starts subtly in the late 20s, becomes more noticeable after age 35, and accelerates further after 40, mainly due to a natural, progressive decrease in the number and quality of remaining eggs (ovarian reserve). This calculator combines published age-banded fecundability figures with a standard cumulative-probability formula to estimate your chances over time, plus guidance based on ACOG's recommended timing for a fertility evaluation. This tool is educational only and is not a substitute for professional medical advice, testing, or diagnosis.

How the calculation works

The calculator first looks up an average monthly fecundability (p) for the age you enter, using published age-band figures that fall from roughly 25% per cycle in the early-to-mid 20s to around 5% or less by the early 40s. It then applies the standard cumulative probability formula used in reproductive epidemiology, P = 1 − (1 − p)ⁿ, where n is the number of monthly cycles. This formula answers "what is the chance of at least one success in n independent monthly trials?" — it is run once using the months you enter to project forward, and again with n = 12 to show a full-year outlook from today.

What this estimate does not include

This is a population-average model, not a personal diagnosis. It does not account for a partner's sperm quality or count, PCOS, endometriosis, tubal or uterine factors, thyroid disorders, ovarian reserve test results (such as AMH level or antral follicle count), body weight, smoking, cycle irregularity, or how frequently and precisely intercourse is timed to ovulation — all of which can meaningfully raise or lower an individual couple's real chances versus the population average shown here.

When to seek a fertility evaluation

The American College of Obstetricians and Gynecologists (ACOG) generally recommends evaluation after 12 months of regular, unprotected intercourse without conception for women under 35, or after 6 months for women 35 and older. Seek evaluation sooner, regardless of these timelines, if you have irregular or absent periods, a known condition affecting fertility, prior pelvic surgery, or other risk factors — a reproductive endocrinologist or your OB/GYN can order appropriate testing for both partners.

Frequently Asked Questions

How does age affect fertility?
Female fertility declines gradually starting in the late 20s, more noticeably after age 35, and more steeply after 40. This is mainly due to a natural decline in both the number and quality of eggs (ovarian reserve) with age. Average per-cycle chances of conception fall from roughly 25% in the early 20s to around 5% or less by the early 40s.
How is the probability of conceiving within a number of months calculated?
This calculator uses the cumulative probability formula P = 1 − (1 − p)ⁿ, where p is the average monthly fecundability (per-cycle chance of conception) for the entered age and n is the number of monthly cycles. This is a standard way epidemiologists model how chances of conceiving add up over repeated cycles of trying.
When should I see a fertility specialist?
The American College of Obstetricians and Gynecologists (ACOG) generally recommends an evaluation after 12 months of regular, unprotected intercourse without conception if you are under 35, or after 6 months if you are 35 or older. Seek evaluation sooner if you have irregular cycles, known reproductive conditions, or other fertility risk factors.
Does this calculator account for male-factor infertility or medical conditions?
No. This tool applies population-average, age-based fecundability figures only. It does not account for a partner's fertility, PCOS, endometriosis, thyroid disorders, ovarian reserve test results (such as AMH or antral follicle count), body weight, smoking, or other individual factors that can raise or lower the true chance of conception. Use it as an educational starting point, not a diagnosis.

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