Estimate the chance of having at least 1, 2, or 3 live-born children delivered by an ending birthday when natural-conception attempts begin at an earlier age. You will also see the model-population average family size and an age-window summary.
Your selected goal
Chance of reaching your selected family size by the delivery deadline
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Average live-born children by your ending age
Modeled age window
Conception chance declines with age in this model. Numbered birth ages are not shown because the people who reach later births form progressively smaller selected groups, so those averages do not form one representative schedule.
Sensitivity range (not a confidence interval)
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This range changes one population-rate assumption in the model. It is not a confidence interval and does not measure your personal uncertainty.
- Age window
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- Selected goal
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- Post-birth wait
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Assumptions and limitations
- Age means the age of the person providing the eggs. The model assumes natural conception with their own eggs, no known infertility, and no previous time trying.
- The selected goal means at least that many live-born children delivered by the ending age. A conception does not count if delivery would occur later.
- The separate average continues attempts after the third birth when time remains; it is not capped at the 1-to-3 goal choices.
- Each successful pregnancy contributes one live-born child. Twins and other multiples are not modeled separately, which may make larger-family estimates slightly conservative.
- Permanent sterility is a modeled reproductive endpoint, not menopause. Its marker is averaged among those not already permanently sterile at the starting age.
- This population estimate cannot account for individual ovulation, partner fertility, health conditions, pregnancy history, treatment, donor eggs, or unplanned pauses.
Methodology
The calculator follows a fixed cohort through 13 modeled conception cycles per year. Each simulated couple has a persistent peak conception probability and an age of permanent sterility. Conception chance declines as that age approaches; conception may end in pregnancy loss or in a live birth after about nine months. After a birth, attempts pause for the selected number of months.
The selected 1-to-3-child goal uses the natural-conception family-completion benchmarks published by Habbema and colleagues. The average family size continues the base simulation beyond a third birth whenever the selected window contains enough time. Later births therefore still contribute to the average.
Conception chance declines with age in this model. Numbered birth ages are not shown because the people who reach later births form progressively smaller selected groups, so those averages do not form one representative schedule. The permanent-sterility marker averages the model distribution among cohort members who are not already permanently sterile at the starting age. It is not a predicted menopause age, medical cutoff, or personal forecast.
The later-birth extension assumes the same conception and pregnancy process at each parity. It does not add postpartum recovery, lactational suppression of ovulation, parity-related changes, secondary infertility, recommended spacing, or pregnancy complications. Those omissions matter most for short waits and large projected family sizes.
The sensitivity range repeats the selected-goal calculation with mean peak monthly fecundability set to 18% and 28% around the 23% base assumption. It changes one model input only and is not a confidence interval.
Primary sources
- Habbema and colleagues, Human Reproduction (2015): desired-family-size endpoint, natural-conception benchmark ages, and the 15-month post-birth default.
- Leridon, Human Reproduction (2004): the reproductive-ageing microsimulation underlying the family-size study.
- Sozou and Hartshorne, PLOS ONE (2012): an open computational cross-check for persistent fecundability and age-related decline.
- American Society for Reproductive Medicine: natural-fertility context and the no-known-infertility population boundary.
This is a population planning model, not an individual prognosis. If you have irregular or absent cycles, a known fertility concern, recurrent pregnancy loss, or prior time trying, ask a clinician about advice that reflects your history.
Frequently asked questions
What does the chance of N children mean?
It is the modeled chance of having at least your selected number of live-born children delivered after attempts begin at the starting age and on or before the ending-age deadline.
Is the average number of children a personal maximum?
No. It is the model-population average under the selected age window and post-birth wait while attempts continue whenever possible. It is not capped at three, but it is not a prediction of your personal family size.
Why does the age window not list average birth ages?
Conception chance declines with age in the model. The people who reach later births form progressively smaller selected groups, so their separate average ages do not form one representative birth schedule. The summary instead shows the starting age, the delivery deadline when applicable, and the modeled reproductive endpoint.
Is the permanent-sterility age the same as menopause?
No. It is a reproductive endpoint used by the population model. The displayed average is limited to modeled cohort members who are not already permanently sterile at the starting age. It is not a menopause date or personal medical cutoff.
Does the calculator include IVF, donor eggs, or known infertility?
No. It models natural conception with the egg provider's own eggs and assumes no known infertility and no previous time trying. Treatment, donor eggs, individual diagnoses, and unplanned pauses can produce different outcomes.
Medical note: This calculator is an educational population estimate, not a fertility test or individual forecast. If you have a known fertility concern, irregular or absent cycles, recurrent pregnancy loss, or prior time trying, ask a qualified clinician about advice that reflects your history. See the medical disclaimer.