Frozen embryo transfer planning involves equal parts hope and arithmetic. Patients naturally ask how likely each transfer is to succeed. They also ask how chances grow across several embryos. This calculator answers both questions with a transparent estimate model. It uses your age at egg retrieval and embryo testing status. Results appear as a per transfer rate and a cumulative chance.
Honesty about limits matters enormously with fertility numbers. Clinic rates vary widely between centres, protocols, and patient groups. This model therefore offers planning guidance, never a personal prediction. It is not medical advice, and it guarantees nothing about outcomes. Your clinic's own audited statistics deserve the greatest weight. Use this page to prepare better questions for your care team.
The model draws on published live birth rates per transfer. Untested blastocysts show a steep decline with rising age. Genetically tested euploid embryos show a much flatter pattern. That contrast surprises many patients at first glance. Sections below explain the reasoning behind both curves. Two worked examples show the arithmetic in full.
What Is a Frozen Embryo Transfer
A frozen embryo transfer is often shortened to FET. Embryos created during an earlier IVF cycle are thawed and transferred. The transfer itself is usually a brief, gentle procedure. No egg collection or fertilisation happens on transfer day. Hormones prepare the uterine lining across the preceding weeks. Timing that lining correctly is central to success.
Most clinics now transfer one embryo at a time. Single embryo transfer greatly reduces risky multiple pregnancies. Remaining embryos stay frozen for possible later attempts. Each thawed embryo therefore represents one separate chance. That structure is exactly why cumulative maths matters here. Several stored embryos mean several sequential opportunities.
Blastocyst is the developmental stage most embryos reach before freezing. A blastocyst is about five or six days old. Embryos reaching this stage have passed early selection naturally. Freezing quality has improved enormously with vitrification techniques. Survival after thawing now exceeds ninety percent at good clinics. Stage and survival both sit behind the published rates.
The frozen approach also separates collection from transfer timing. That gap lets hormone levels settle after stimulation drugs. Many specialists believe a calmer cycle helps the lining. Patients also gain time for genetic testing results. Scheduling becomes more flexible for work and family life. These practical benefits explain the worldwide shift toward frozen transfers.
Why Age at Retrieval Drives the Rates
Eggs age with the person who produced them. Chromosome errors inside eggs rise steadily after the mid thirties. Such errors are the main reason embryos fail to implant. They also explain most early miscarriages in IVF treatment. The uterus, by contrast, ages far more slowly. Frozen transfer therefore keys success to retrieval age.
An embryo created at 32 keeps its 32 year old prospects. Transferring it at 38 does not age the embryo further. This is why the calculator asks for age at retrieval. Patients who banked embryos young often find this reassuring. It also explains the popularity of embryo banking strategies. Freezing earlier preserves younger biology for later family building.
The untested rates in this model reflect that egg ageing. Under 35, each untested blastocyst carries a 45 percent estimate. By ages 41 to 42, the estimate falls to 20 percent. Past 42, it drops to 10 percent per transfer. These are population averages across many clinics and patients. Individual prognosis can sit well above or below them.
Sperm quality plays a smaller, but real, supporting role here. Severe male factor issues can reduce embryo development rates. Once a blastocyst forms, though, egg age dominates outcomes. Couples sometimes blame the wrong side of the equation. Balanced counselling addresses both partners' contributions from the start.
Tested Versus Untested Embryos
PGT-A testing checks embryos for the correct chromosome count. Embryos with the full set are called euploid. Those with extra or missing chromosomes are called aneuploid. Transferring a euploid embryo removes the largest single failure cause. Per transfer success therefore rises and steadies considerably. This model uses euploid rates between 55 and 46 percent.
Notice how flat the euploid curve stays across ages. Published meta analyses report roughly 55 percent under 35. Even past 42, euploid transfers hold near 46 percent. Testing effectively filters out age related chromosome errors beforehand. Fewer euploid embryos are available at older ages, though. The challenge shifts from transfer success to obtaining one.
Testing involves cost, biopsy, and some difficult decisions. Not every clinic recommends it for every patient. Younger patients with many embryos may gain little from testing. Older patients may value avoiding transfers doomed by aneuploidy. Your specialist can weigh these trade offs for your situation. This calculator simply shows both rate sets side by side.
Biopsy removes a few cells from the embryo's outer layer. Those cells would otherwise become part of the placenta. Modern studies find the procedure safe in experienced hands. Results usually return within one to two weeks. Patients then learn how many embryos are euploid.
How to Use the Fet Success Rate Calculator
Three quick inputs drive the estimate above. Follow these steps in order.
- Choose the age band that matches your age at egg retrieval.
- Select whether the embryos are untested or PGT-A euploid.
- Enter how many embryos you have available, from one to six.
- Press the blue Calculate button to see both estimates.
- Read the per transfer rate before the cumulative figure.
- Press the yellow Reset button before changing your scenario.
Age at retrieval means the age when eggs were collected. Using your current age instead would distort the estimate badly. Check your clinic paperwork if the retrieval date feels fuzzy. Embryo counts should include only embryos actually frozen and stored. Planned future cycles belong in a separate calculation entirely. Clean inputs keep the planning value of this tool.
The result gives three figures for your scenario. First comes the estimated live birth chance per transfer. Second comes the cumulative chance across all your embryos. Third comes the average number of transfers per live birth. Together they support realistic financial and emotional planning. Share them with your clinic at your next review.
Worked Example 1: Under 35 With Three Untested Embryos
The Inputs
Consider a patient whose eggs were collected at age 33. She has three untested blastocysts in storage now. Her age band is therefore under 35 in the model. The untested rate for that band is 45 percent. Each single embryo transfer carries that same starting estimate. Her question is what three embryos offer together.
The Calculation
Cumulative chance uses the formula one minus one minus p, raised to N. Here p is 0.45 and N is 3. One minus 0.45 leaves 0.55 per failed transfer. Cubing 0.55 gives 0.166375, and one minus that gives 0.833625. Average transfers equal one divided by 0.45, about 2.22.
The Result
Her cumulative estimate reaches 83.36 percent across three transfers. Each individual transfer still carries the 45 percent figure. On average, about 2.22 transfers produce one live birth here. These numbers assume each transfer behaves independently of the others. Her clinic may quote different figures from its own data.
Worked Example 2: Ages 38 to 40 With Two Euploid Embryos
The Inputs
Now consider a patient whose retrieval happened at age 39. Testing left her with two euploid blastocysts in storage. Her age band is 38 to 40 in this model. The euploid rate for that band is 50 percent per transfer. She wants the combined outlook for both embryos. Emotional planning matters as much as arithmetic here.
The Calculation
Apply the same cumulative formula with p equal to 0.50. One minus 0.50 leaves 0.50 for each transfer. Squaring 0.50 gives 0.25 exactly for two transfers. One minus 0.25 gives a cumulative figure of 0.75. Average transfers equal one divided by 0.50, exactly 2.
The Result
Her cumulative estimate reaches 75 percent across two transfers. Each transfer individually carries the 50 percent euploid estimate. Testing has flattened the age penalty she might otherwise face. Compare the untested rate of 30 percent for her band. The contrast explains why her clinic discussed testing.
Reading the Cumulative Chance
Cumulative figures grow with every additional embryo available. Growth slows, though, because each transfer multiplies a shrinking remainder. Going from one to two embryos adds a large jump. Going from five to six adds a much smaller one. This pattern is called diminishing returns in probability. It helps families weigh further retrieval cycles realistically.
Independence is the model's biggest simplifying assumption. Real transfers are not perfectly independent events in practice. A uterus related issue can affect every attempt similarly. Conversely, clinicians learn from each failed transfer and adjust. Protocols change lining preparation, timing, or further testing accordingly. Reality can therefore beat or trail the model either way.
Never read a cumulative figure as a promise. An 83 percent estimate still includes a 17 percent miss chance. Conversely, a 20 percent estimate succeeds for one in five patients. Probability describes groups across many similar treatment cycles. Your personal outcome will be binary: success or not. Planning should respect both the hope and the uncertainty.
Partners often read the same percentage very differently. One may hear strong hope where another hears real risk. Talking through both readings prevents conflict during treatment weeks. Agree in advance how many transfers you will attempt. Also agree when you will review that decision together. Shared plans protect relationships as well as budgets.
What This Model Leaves Out
Embryo grading details do not enter this estimate model. Clinics grade blastocysts by appearance alongside genetic status. Top graded embryos may outperform the averages used here. Lining thickness and pattern also influence implantation chances. These clinical details live in your personal treatment file. Only your clinic can weigh them properly.
Diagnosis matters as well across different patient groups. Endometriosis, fibroids, and male factor issues all shift outlooks. Body weight, smoking, and prior transfer history add further variation. Clinic laboratory quality creates another genuine layer of difference. Published population rates smooth all of that away. Expect your personalised estimate to differ from this page.
Treat this page as education, not medical advice. It cannot diagnose, prescribe, or predict your personal result. Decisions about testing, banking, or further cycles belong with specialists. Ask your clinic for its own rates by age and embryo type. Compare those with this model during your consultation. Informed questions lead to calmer, better decisions.
Tips for Using the Fet Success Rate Calculator
Careful framing turns raw percentages into useful planning.
- Always enter age at egg retrieval, never your current age.
- Run tested and untested scenarios separately when deciding about PGT-A.
- Ask your clinic for its own live birth rates by age band.
- Plan finances using the per transfer rate, not only cumulative hope.
- Recalculate after each transfer, since embryo counts change.
- Discuss single embryo transfer benefits with your specialist.
- Share results with your partner before making cycle decisions.
- Remember that a missed transfer still leaves real chances behind.
Emotional pacing deserves a place in every treatment plan. Breaks between transfers help many patients recover perspective. Support groups and counselling reduce the isolation of treatment. Numbers should serve your planning, not dominate your life. Step away from calculators when they stop helping.
Frequently Asked Questions
General Questions
1. What does this calculator estimate?
It estimates live birth chances for frozen embryo transfers. Inputs are age at retrieval, embryo testing status, and embryo count. Outputs show a per transfer rate, a cumulative chance, and average transfers per live birth.
2. Is this calculator medical advice?
No, this page provides general education and planning estimates only. It cannot assess your health, diagnosis, or personal prognosis. Always discuss treatment decisions with your own fertility specialist, who knows your complete medical history.
3. Why do clinic rates vary so much?
Clinics differ in patient mix, laboratory quality, and transfer protocols. A clinic treating many older patients shows lower headline rates. Compare clinics using age stratified data rather than single overall percentages whenever possible.
4. What does euploid mean?
A euploid embryo carries the correct number of chromosomes. PGT-A testing identifies euploid embryos before transfer takes place. Because chromosome errors cause many failures, euploid transfers succeed more often and more consistently across ages.
5. Does a frozen transfer work as well as a fresh one?
Modern vitrification gives frozen transfers outcomes comparable to fresh transfers. Many clinics now freeze all embryos by deliberate strategy. Your specialist will explain whether a freeze all approach suits your particular treatment plan.
How the Calculation Works
6. How is the cumulative chance calculated?
The formula is one minus one minus p, raised to the number of transfers. Here p is the per transfer chance as a decimal. This assumes each transfer is an independent event with the same probability.
7. Why does age at retrieval matter more than age at transfer?
Chromosome quality is set when the egg forms the embryo. Freezing preserves that embryo's biology at the retrieval age. The uterus ages slowly by comparison, so retrieval age drives the rates in this model.
8. Why are euploid rates so flat across ages?
Testing removes aneuploid embryos, which become commoner with age. The euploid embryos that remain perform similarly at most ages. Published meta analyses place their live birth rates roughly between 55 and 46 percent.
9. What does average transfers mean?
It is one divided by the per transfer chance. A 50 percent rate therefore averages two transfers per live birth. Averages describe groups, so your own path may take fewer or more attempts.
10. Can I enter more than six embryos?
The form accepts between one and six embryos by design. Most patients store numbers within that range for planning. If you hold more, calculate six first, then consider the remainder as a separate scenario.
Practical Questions
11. Should I test my embryos with PGT-A?
That decision depends on age, embryo numbers, history, and budget. Testing raises per transfer rates but reduces embryos available for transfer. Your specialist can model both paths using your clinic's actual laboratory data.
12. What if I used donor eggs?
Use the donor's age at retrieval in this model. Embryo biology follows the egg provider's age, not the recipient's. Mention donor status to your clinic when comparing their quoted rates with these estimates.
13. Why did my clinic quote a different rate?
Clinics quote from their own audited results and patient population. Their figures may also count pregnancy rather than live birth. Ask exactly which outcome and age group any quoted rate describes before comparing numbers.
14. Does embryo grade change the estimate?
Yes, grading can shift chances above or below these averages. This simplified model does not include grade, lining, or diagnosis. Treat its output as a starting point for discussion, never as your personalised prognosis.
15. Is a high cumulative chance a guarantee?
No percentage here guarantees any individual outcome at all. A cumulative 90 percent still leaves one in ten patients unsuccessful. Conversely, low estimates succeed for a meaningful minority of patients in every band.
CONCLUSION
One patient saw 45 percent per transfer become 83.36 percent across three embryos. Another saw euploid testing hold her rate at 50 percent, reaching 75 percent across two. Both examples show how age, testing, and embryo count interact. Use this estimate model to plan questions, budgets, and expectations calmly. Then lean on your clinic's data and advice for the decisions that truly matter.