IUI carries a per-cycle success rate of roughly 10 to 20 percent. That is lower than most patients expect, but it is a real chance with the right diagnosis, at the right age, and over a fair number of attempts. These numbers can't predict your own result. What they do show is when IUI is a reasonable choice, and when your time is better spent on another treatment.
IUI success rate by age, decade by decade
Age is the strongest single predictor because it reflects egg quality, which no test directly measures and no medication corrects. Published series consistently show a pattern:
| Age group | Approximate per-cycle success rate | What it reflects |
|---|---|---|
| Under 35 | 15–20% | Egg quality is typically at its best; IUI's per-cycle odds are at their highest |
| 35–37 | 12–15% | A gradual decline — still a reasonable window for IUI, but the timeline before reassessing shortens |
| 38–40 | 8–12% | The decline steepens; cumulative odds across three to four cycles narrow meaningfully |
| Over 40 | 3–9% | Per-cycle odds are low enough that most specialists weigh the time cost of IUI against what IVF can offer |
At exactly age 35: this is simply where published studies divide their age groups. Nothing changes suddenly on your birthday. A 35-year-old's odds sit close to the top of the "35–37" band above — very similar to a 34-year-old's, and only slightly different from a 37-year-old's. The age bands describe a gradual decline in egg quality. These are averages from published clinical studies — rough ranges, not fixed numbers. Your individual odds depend on diagnosis, medication protocol, sperm quality, and whether ovulation timing was precise. No calculator can replace the judgment your doctor makes cycle by cycle.
How diagnosis changes the picture
The same per-cycle percentage looks very different depending on why you are doing IUI:
| Diagnosis | How it affects IUI odds |
|---|---|
| Unexplained infertility | IUI with ovarian stimulation is often the evidence-supported first step — the combination addresses timing and mild egg-pickup issues that testing cannot detect |
| Mild male factor | When sperm count or motility is moderately reduced, washing and concentrating the sample can meaningfully improve the number of motile sperm reaching the egg |
| Ovulation disorders (PCOS and others) | If the primary issue is irregular or absent ovulation, medication-plus-IUI addresses the root cause directly — success rates in this group often sit at the higher end of the range |
| Cervical-factor infertility | Bypassing the cervix is precisely what IUI does; per-cycle odds here can be comparable to the general population's natural conception rate |
| Significant male factor | When sperm results are too low even after the sample is washed, IUI's odds drop substantially — ICSI via IVF deals with the fertilisation step directly |
| Tubal disease | IUI requires at least one open tube; blocked or significantly damaged tubes make IUI unsuitable regardless of other factors |
| Low ovarian reserve | Fewer eggs per cycle means lower odds each cycle, and the time spent on repeated attempts matters more |
The diagnosis does not replace age; both count. A 28-year-old with mild male factor has different odds from a 39-year-old with the same semen analysis, even though the diagnosis is the same.
Stimulated versus natural-cycle IUI
Most published success rates refer to stimulated IUI — cycles where medication (oral or injectable) encourages one or two follicles to mature. Natural-cycle IUI, where no medication is used and the body's own single egg is the target, carries lower per-cycle odds — roughly 5 to 10 percent depending on age and diagnosis. The difference is not dramatic per cycle, but it adds up over three to four attempts.
This matters when interpreting any number you read online. A success rate quoted without specifying whether it was medicated is not comparable to one that does.
Cumulative success across cycles
Per-cycle odds are modest, but they accumulate:
| Cycles completed (stimulated) | Approximate cumulative chance of pregnancy (under 35, no severe factor) |
|---|---|
| 1 | 15–20% |
| 2 | 25–35% |
| 3 | 35–45% |
| 4 | 40–50% |
After three to four cycles, the curve flattens — each additional attempt adds proportionally less. This is why most specialists suggest reassessing at three to four cycles rather than continuing indefinitely: most of the benefit of IUI comes within those first few cycles.
For patients over 38 or with significant factors, the cumulative curve is shallower and flattens earlier, which is why the decision to move to IVF comes sooner in those situations.
What these numbers cannot tell you
Success-rate tables describe populations, not individuals. Three things they reliably do not capture:
- Your specific egg and sperm quality. Tests measure quantity and movement, not the chromosomal health of a particular egg or sperm cell. Two patients with identical reports can have very different outcomes.
- Cycle-to-cycle variation. Medication response, follicle count, lining thickness, and timing precision all vary between attempts — one weaker cycle does not decide how the next one goes.
- The emotional weight. A 15 percent chance means roughly one in seven — real, but also five or six cycles that end with a negative test. Preparing for the emotional reality of those odds, not just the mathematical ones, matters.
Success rates describe populations, not your outcome — the most useful thing they tell you is whether IUI is a reasonable path for your situation, and for how long.
Frequently asked
Is a 15 percent success rate low?
It depends on the comparison. Natural conception per cycle in fertile couples is roughly 20 to 25 percent — IUI is not dramatically lower, especially when the cause of difficulty is something IUI specifically addresses (timing, mild male factor, cervical bypass). What makes it feel low is the expectation that treatment should be substantially more effective than trying naturally, which for IUI is not always the case.
Do success rates include pregnancies that ended in miscarriage?
This varies by source. Some report clinical pregnancy rates (a pregnancy confirmed on scan), which include early losses; others report live-birth rates, which are lower. When comparing numbers, check which definition is being used — a clinical pregnancy rate of 18 percent and a live-birth rate of 12 percent from the same dataset are not contradictory, they are measuring different things.
Should I choose a clinic based on its IUI success rates?
Be cautious. Published success rates vary widely depending on patient selection — a clinic that accepts only straightforward cases will report higher numbers than one that treats complex diagnoses, without necessarily being better. Ask how many IUI cycles the clinic performs, what age and diagnosis mix they see, and whether their quoted rate is per cycle or cumulative. Those details matter more than a headline number.
At what point do the numbers say IUI is not worth trying?
When per-cycle odds are consistently below 5 percent — which typically means significant male factor, tubal compromise, markedly low reserve, or age over 40 with additional factors — the time and emotional cost of sequential attempts may outweigh the probability of success. Your doctor's judgment, not a table, makes that call.
What is the success rate of a 4th IUI cycle, specifically?
Published series mostly report cumulative success across cycles rather than the isolated odds of "just the 4th try," but the pattern is consistent: each additional cycle adds less than the one before it. From the cumulative table above (under 35, no severe factor), the jump from cycle 3 to cycle 4 adds only about 5 percentage points to the cumulative chance of pregnancy, compared with the larger jumps from cycle 1 to 2 and 2 to 3. This is why most specialists suggest reassessing at three to four cycles rather than continuing indefinitely. A 4th cycle still has real odds; it just adds less than the cycles before it.
What are the risks and side effects of an IUI cycle itself?
Mostly medication-related — bloating, tenderness, mild spotting — with a small chance of OHSS and a somewhat higher chance of twins with stimulated cycles. IUI side effects, risks, and the pregnancy-test timeline covers the full list, including why testing before your clinic's recommended day can mislead you.