If you are starting IUI, one number matters more than any other: your age. Across widely reported clinic data, IUI leads to a clinical pregnancy in roughly 15–20% of cycles for women under 35, about 10% per cycle at ages 35–37, and single digits per cycle after 40. Those are per-cycle figures — and the cumulative odds across several cycles tell a more hopeful story than any single number suggests.
Below are the real numbers by age band, what "success" actually means in clinic statistics, the simple math behind cumulative odds, and the factors beyond age that move your chances.
What Are IUI Success Rates Under 35?
Under 35, IUI works in roughly 15–20% of cycles (clinical pregnancy rate), with live birth rates a few points lower at about 10–15% per cycle.
This is the age band with the best IUI prognosis, which is why fertility guidelines commonly suggest trying 3–4 IUI cycles before considering IVF when the diagnosis is unexplained infertility or mild male-factor issues. A typical cycle involves ovarian stimulation with oral medication, ultrasound monitoring of follicle growth, a trigger shot to time ovulation, and the insemination procedure itself — usually completed within a single morning appointment. Younger eggs mean fewer chromosomal errors, better embryo quality, and a uterine environment more likely to support implantation — the three biological levers that drive every fertility statistic. If you want a rough sense of your monthly odds from intercourse or treatment, a pregnancy chance calculator can put age-based probabilities in perspective.
What Are IUI Success Rates at 35–37?
Between 35 and 37, the per-cycle clinical pregnancy rate falls to roughly 10%.
The decline is gradual at first, then accelerates. Egg quantity (ovarian reserve) and egg quality both begin dropping more steeply after 35, which is the main reason the numbers step down. Many clinics still recommend IUI in this band — particularly with ovulation medication — but doctors tend to suggest fewer cycles (often 2–3) before discussing IVF, since time matters more now. Published summaries from fertility societies (such as ASRM practice guidance updated through 2023) consistently show this inflection point in the mid-30s.
What Are IUI Success Rates at 38–40?
From 38 to 40, IUI success drops to roughly 5–8% per cycle.
At this stage, age-related egg quality decline dominates the outcome. Clinics often counsel patients in this band to move to IVF sooner rather than later, because IVF with genetic screening of embryos can compensate for the higher rate of chromosomal abnormalities. That said, IUI is still a reasonable, lower-cost first step for some diagnoses — the key is going in with realistic expectations and a clear plan for how many cycles to attempt. For context on the alternative path, our IVF due date calculator shows how IVF timing translates into a due date.
What Are IUI Success Rates Over 40?
Over 40, per-cycle IUI pregnancy rates fall to low single digits — roughly 2–5%.
These are sobering numbers, and honest clinics share them upfront. After 40, the proportion of chromosomally normal eggs drops sharply, which is why most fertility specialists recommend IVF (often with donor eggs discussed as an option) rather than repeated IUI cycles. IUI is rarely harmful to try once or twice, but each month spent on a low-probability treatment is a month of declining odds — a trade-off worth discussing frankly with your doctor.
Per-Cycle vs Cumulative: What 3 Cycles Really Add Up To
Here is the insight most articles skip: per-cycle rates understate your real chances, because cumulative odds compound. The formula is simple:
Cumulative success = 1 − (1 − p)ⁿ, where p is the per-cycle rate and n is the number of cycles.
Worked example: at an 18% per-cycle rate (typical under 35), three cycles give 1 − (0.82)³ = 1 − 0.551 ≈ 45% cumulative chance of at least one clinical pregnancy. At a 10% per-cycle rate (ages 35–37), three cycles give 1 − (0.90)³ ≈ 27%. A fourth cycle at 18% pushes the cumulative figure to about 55%. This is exactly why the standard advice is a course of IUI — usually 3–4 cycles — rather than judging the treatment on a single attempt. Each cycle is an independent roll of the dice, and the dice get rolled again.
Why Clinic-Reported IUI Numbers Vary So Much
If you have seen wildly different IUI success rates online, here is why: clinics are not reporting the same thing.
- Patient mix matters most. A clinic whose IUI patients average 32 will report far higher rates than one averaging 39 — even with identical skill. National summaries (such as SART's 2022 clinic report, published in 2024) show how steeply outcomes track female age.
- "Success" is defined differently. A positive pregnancy test rate is always higher than a clinical pregnancy rate (heartbeat on ultrasound), which is higher than a live birth rate. Early losses — including chemical pregnancy — explain much of the gap between a positive test and a baby.
- Medication protocols differ. Natural-cycle IUI, Clomid/letrozole IUI, and injectable-gonadotropin IUI have different success rates — and very different multiple-pregnancy risks (twin rates can reach 10–20% with injectables, versus ~5–8% with oral medication).
- The trigger shot confuses testing. The hCG trigger used before IUI can linger in your system and cause a wrong positive pregnancy test if you test too early — another reason "pregnancy rate" needs a definition attached.
Always ask a clinic: is that clinical pregnancy or live birth, per cycle started, and for women my age?
What Else Moves Your IUI Odds Besides Age?
Age leads, but four other factors meaningfully shift the numbers:
Sperm parameters
IUI was designed for mild male-factor infertility. Most clinics look for at least 5–10 million motile sperm after washing; below that threshold, per-cycle rates fall and IVF with ICSI is usually recommended instead.
Your diagnosis
IUI works best for unexplained infertility, mild male factor, and ovulation disorders. It cannot overcome blocked fallopian tubes or severe endometriosis — for those, IVF is the appropriate treatment from the start.
Medication protocol
Ovulation medication roughly doubles IUI success compared with natural-cycle IUI in many published series, at the cost of higher multiple-pregnancy risk. Oral medications (letrozole, Clomid) are the usual first step; injectables are more powerful but require close monitoring.
Timing precision
IUI is typically performed 24–36 hours after the hCG trigger shot, aligning insemination with ovulation. Precise timing is one of the few variables you and your clinic fully control.
When Do Doctors Recommend Moving From IUI to IVF?
The usual guidance: after 3–4 unsuccessful IUI cycles under 35, or 1–2 cycles at 38 and above, most specialists recommend a serious conversation about IVF.
This is not a failure — it is statistics. IVF per-cycle live birth rates are substantially higher (SART's 2022 national data put IVF live birth per embryo transfer above 50% for patients under 35), because it bypasses several steps where IUI can fail: fertilization, embryo development, and selection of the best embryo. The trade-off is cost and invasiveness, which is why IUI remains the sensible first step for good-prognosis patients.
If your IUI cycle worked, congratulations — find out when your baby is due with our free IUI due date calculator.