Fertility by Age & Conception Odds
Last reviewed: April 2026
Estimate your fertility by age. See chances of natural conception per cycle, cumulative probability over months, and when to seek help. This calculator runs entirely in your browser — your data stays private, and no account is required.
Female fertility peaks in the early-to-mid 20s and begins a gradual decline around age 30, with a sharper drop after 35. This is primarily driven by egg quantity and quality — both decline with age. At birth, a female has about 1–2 million eggs. By puberty, roughly 300,000–400,000 remain. By age 37, the average is about 25,000. By 40, approximately 5,000–10,000. Quality also declines, with higher rates of chromosomal abnormalities in older eggs.
Under 25: ~25–30% chance per cycle. ~90% conceive within 12 months. 25–29: ~25% per cycle. ~85% within 12 months. 30–34: ~20% per cycle. ~75% within 12 months. 35–37: ~15% per cycle. ~66% within 12 months. 38–40: ~10% per cycle. ~50% within 12 months. Over 40: ~5% per cycle. ~30% within 12 months. These are averages for couples without known fertility issues.
Male fertility also declines with age, though more gradually. Sperm count, motility, and morphology decrease starting around age 40. Men over 45 have lower conception rates and slightly higher risks of miscarriage and certain genetic conditions in offspring. Lifestyle factors (smoking, alcohol, heat exposure, obesity) can significantly affect sperm quality at any age.
Under 35: Seek evaluation after 12 months of regular unprotected intercourse without conception. 35–39: After 6 months. 40+: Consider evaluation immediately or after 3 months. Known issues (irregular periods, endometriosis, PCOS, prior surgery, male factor concerns): consult a reproductive endocrinologist sooner.
Timing intercourse: The fertile window is roughly 5 days before ovulation through ovulation day. Use our Ovulation Calculator to estimate your window. Maintain healthy weight: BMI 19–24 is optimal. Both underweight and overweight reduce fertility. Limit alcohol and caffeine: Moderate caffeine (<200mg/day) is generally considered safe. Don't smoke: Smoking accelerates egg loss and reduces IVF success rates by 50%.
Egg freezing: Most effective before age 35. Success rates decline significantly after 38. Costs $10,000–15,000 per cycle plus annual storage. Embryo freezing: Higher success rates than egg freezing but requires a sperm source at the time of freezing. AMH testing: Anti-Müllerian Hormone blood test estimates remaining egg supply (ovarian reserve) — useful for planning but doesn't predict natural conception odds directly.
| Cycle Day | Event | Fertility Level | Conception Chance |
|---|---|---|---|
| Day 1-7 | Menstruation | Very low | <1% |
| Day 8-11 | Pre-ovulation | Rising | 5-10% |
| Day 12-13 | Fertile window peak | High | 15-25% |
| Day 14 | Ovulation (avg) | Highest | 25-33% |
| Day 15-16 | Post-ovulation | Declining | 5-10% |
| Day 17-28 | Luteal phase | Very low | <1% |
Fertility is fundamentally a game of probabilities — and those probabilities shift dramatically based on age, timing, health status, and environmental factors. Understanding the realistic odds of conception per cycle helps couples set appropriate expectations and know when to seek medical assistance.
For a healthy couple having well-timed intercourse during the fertile window, the probability of conception per cycle (called fecundability) peaks in the early-to-mid twenties at approximately 25–30% per cycle. By age 30, this drops to roughly 20%. At 35, it falls to about 15%. At 40, the per-cycle rate is approximately 5–10%, and by 45, it drops below 3%. Cumulative probability over 12 cycles paints a more practical picture: approximately 85–90% of couples under 35 conceive within one year of trying, compared to about 75% of couples age 35–39 and roughly 50% of couples over 40.
These declining odds result from two simultaneous processes: decreasing egg quantity (ovarian reserve) and decreasing egg quality (rising rates of chromosomal abnormalities). At age 25, roughly 75% of eggs are chromosomally normal. By 35, about 50% are normal. By 40, only 20–30% are normal. Chromosomally abnormal eggs either fail to fertilize, fail to implant, or result in early miscarriage — explaining why miscarriage rates climb from 10% in the 20s to 33% by age 40 and 50%+ by age 45.
While female age receives most attention, male fertility also declines with age — just more gradually. Sperm quality (motility, morphology, and DNA fragmentation) begins declining around age 40. Advanced paternal age (over 45) is associated with increased rates of miscarriage, certain genetic conditions in offspring, and longer time to conception. A standard semen analysis evaluates count (15+ million/mL is normal), motility (40%+ should be motile), and morphology (4%+ should have normal shape using strict Kruger criteria). Factors that impair sperm quality include heat exposure (saunas, hot tubs, tight clothing, laptop use), smoking, heavy alcohol use, certain medications, anabolic steroids, and obesity.
Body weight: Both underweight (BMI below 18.5) and obese (BMI above 30) women experience reduced fertility. Excess body fat disrupts estrogen regulation and can cause anovulation. Low body fat suppresses the hypothalamic-pituitary-ovarian axis entirely — a condition called hypothalamic amenorrhea, common in athletes and those with eating disorders. Even modest weight changes (5–10% of body weight) can restore ovulation in many cases. Smoking: Reduces female fertility by approximately 50% and accelerates egg loss by 1–4 years — a 35-year-old smoker may have the ovarian reserve of a 39-year-old nonsmoker. Alcohol: Moderate-to-heavy drinking (7+ drinks per week) is associated with reduced fertility, though light consumption shows minimal effect in most studies. Caffeine: Consumption under 200 mg/day (roughly one 12-oz coffee) appears safe; higher intake is associated with slightly increased miscarriage risk.
Standard medical guidance recommends evaluation after 12 months of unprotected, well-timed intercourse for women under 35, and after 6 months for women 35 and older. Evaluation should begin immediately if there are known risk factors: irregular or absent periods, known endometriosis, history of pelvic inflammatory disease, prior cancer treatment, or known male factor issues. The basic fertility workup includes hormonal blood tests (FSH, estradiol, AMH, thyroid, prolactin), pelvic ultrasound for ovarian follicle count, hysterosalpingogram (HSG) to assess tubal patency, and semen analysis for the male partner.
Treatment escalates based on diagnosis. Ovulation induction (letrozole or clomiphene) costs $50–$500/cycle and is first-line for anovulatory infertility. IUI (intrauterine insemination) places washed sperm directly in the uterus during ovulation, costing $500–$2,000/cycle including monitoring — effective for mild male factor, cervical factor, or unexplained infertility. IVF (in vitro fertilization) costs $15,000–$25,000/cycle including medications, with success rates of 40–50% per cycle under age 35, declining to 10–20% over age 40. Egg freezing (oocyte cryopreservation) offers fertility preservation for women who want to delay childbearing — the procedure costs $8,000–$15,000 plus $500–$1,000/year for storage. Optimal freezing age is under 35, when egg quality is highest.
Fertility treatment takes a significant emotional and financial toll. The average couple undergoes 2–3 IVF cycles before achieving a live birth, bringing total costs to $40,000–$75,000. Some states mandate insurance coverage for fertility treatments — currently 21 states have some form of fertility insurance mandate, though coverage details vary widely. Employer-sponsored fertility benefits have expanded dramatically in recent years, with many large companies offering $20,000–$50,000+ in lifetime fertility coverage. Before starting treatment, research your insurance benefits thoroughly, explore financing options (many clinics offer payment plans or partner with fertility lenders), and consider the emotional support resources available — counseling, support groups, and online communities can be invaluable during what many describe as one of life's most stressful experiences.
See also: Ovulation Calculator · Due Date Calculator · Pregnancy Calculator · Menstrual Cycle · Pregnancy Weight Tracker
→ Age is the single most important fertility factor. At 25, per-cycle conception rate is ~25%. At 30: ~20%. At 35: ~15%. At 40: ~5%. These are population averages — individual variation is enormous, but the trend is consistent and well-documented.
→ Timing intercourse to the fertile window matters most. The fertile window is approximately 5 days before ovulation plus the day of ovulation itself. Sperm survive up to 5 days; the egg survives 12–24 hours. Our Ovulation Calculator can help identify this window.
→ See a specialist earlier if you're over 35. Under 35: try for 12 months before seeking evaluation. Over 35: seek evaluation after 6 months. Over 40: seek evaluation immediately. These guidelines exist because time is a meaningful factor in treatment success.
→ Male factors account for 40–50% of infertility cases. A semen analysis is simple, inexpensive, and should be done early in any fertility evaluation. Both partners should be evaluated simultaneously rather than assuming the issue is with one person.
See also: Ovulation Calculator · Pregnancy Calculator · Due Date Calculator · Menstrual Cycle