For couples going through in vitro fertilization (IVF), the due date is not a guess based on an uncertain last period — it is pinned to a precise moment. Because the embryologist knows exactly when fertilization happened and exactly when the embryo was placed back into the uterus, an IVF due date is usually more accurate than a due date estimated from a regular menstrual cycle. This Smekys IVF due date calculator turns your embryo transfer date into an estimated due date (EDD), your likely fertilization date, your LMP-equivalent date, and your current pregnancy week. Whether you call it a blastocyst due date calculator for a day-5 transfer or a frozen embryo transfer (FET) planner, the same transfer-date math applies.
The math is deliberately simple. A day-5 blastocyst transfer means the embryo has already spent five days growing before transfer, so you add 261 days to the transfer date. A day-3 cleavage-stage transfer means the embryo is younger, so you add 264 days. The three-day gap between the two rules is why selecting the correct embryo stage matters: choosing the wrong one shifts your EDD by three full days.
How to Use
- Enter the Embryo Transfer Date — the exact calendar date your fertility clinic transferred the embryo(s). This works for both a fresh transfer and a frozen embryo transfer (FET), because the clock is anchored to the transfer itself, not to egg retrieval.
- Set the Embryo Stage at Transfer to 5 if you had a blastocyst transfer (day 5 or day 6), or 3 if you had an earlier cleavage-stage transfer. Your IVF cycle summary lists this; the most common transfers today are day-5 blastocysts.
- Optionally set Calculate Pregnancy As Of to the date you want your current week measured against. It defaults to today, so the moment you open the page you will see how many weeks and days pregnant you are.
- Read the result card: the highlighted Estimated Due Date (EDD) is the headline number, with the estimated fertilization date, your LMP-equivalent date, current week, days pregnant, and days remaining.
A quick worked check: a transfer on March 15, 2026 with a day-5 blastocyst adds 261 days and lands on December 1, 2026. The same transfer date with a day-3 embryo adds 264 days and lands on December 4, 2026.
What the Results Mean
The highlighted Estimated Due Date (EDD) is the headline date to plan around — about 40 weeks from the LMP-equivalent date the clinic back-calculates. The Estimated Fertilization Date is simply your transfer date minus the embryo's age in days; the LMP-Equivalent Date adds 14 days before that, matching the way obstetricians date a natural pregnancy. Current Pregnancy Week and Days Pregnant tell you where you are today, and Days Until Due Date counts down to EDD. Treat the week number as a planning guide, not a promise: only a minority of babies are born exactly on their EDD, and your first-trimester ultrasound is the clinic's final tie-breaker.
Why IVF Due Dates Are Different
In a natural conception, doctors use Naegele's rule: take the first day of the last menstrual period and add 280 days. That rule assumes ovulation happens around day 14, but many women ovulate earlier or later, which is why only about 5% of babies are actually born on their estimated due date.
IVF removes that uncertainty. The embryologist fertilizes the egg in the lab on a known day, and the transfer happens on a known day. Clinics therefore back-calculate a "gestational age" as if a standard 28-day cycle had occurred: they treat the pregnancy as 14 days along at fertilization. A day-5 blastocyst transferred on date T is already 19 gestational days old, so the remaining time to the 280-day target is 280 minus 19, or 261 days. A day-3 cleavage embryo follows the same 280-day target using the widely accepted clinic convention of 264 days added to transfer. This calculator uses those two published offsets — 261 for a day-5 blastocyst, 264 for a day-3 embryo — which is exactly why selecting the correct stage moves your EDD by three days.
Your ultrasound at the first trimester nuchal scan will still be the clinic's reference point. If the ultrasound measures a gestational age that differs by more than about five to seven days from the transfer-based estimate, your doctor may adjust the due date.
Day-3 vs Day-5 Transfers
- Day-5 blastocyst transfer (add 261 days). Blastocysts have developed to a fluid-filled ball of cells and are generally more robust. Because they are more developed, the transfer-based EDD sits slightly earlier.
- Day-3 cleavage transfer (add 264 days). These embryos are still in early cell division. The extra three days built into the formula account for the younger stage.
If your clinic transferred a day-6 blastocyst, treat it as a day-5 blastocyst in this calculator and ask your embryologist whether they apply a one-day adjustment.
Examples
Example 1 — A fresh day-5 transfer. A couple has a blastocyst transferred on March 15, 2026. They enter embryo stage 5. The calculator adds 261 days and shows an EDD of December 1, 2026, an estimated fertilization date of March 10, and an LMP-equivalent date of February 24. Measured on October 25, they are about 34 weeks pregnant with 37 days to go.
Example 2 — A frozen embryo transfer (FET) on the same date. The same couple uses a cryopreserved day-3 embryo transferred on March 15, 2026. Because the embryo is stage 3, the calculator adds 264 days and moves the EDD to December 4, 2026 — three days later. This illustrates why the embryo-stage field is not optional.
Example 3 — Planning around cost and timing. A single IVF cycle in the United States commonly costs $12,000–$20,000 before medications, and live birth rates per started cycle vary widely with maternal age — roughly 30–40% for patients under 35 and falling steadily after that. Couples often schedule a second attempt or an embryo biopsy around the first EDD; entering the transfer date here gives the clinic a shared timeline to plan ovarian stimulation, monitoring, and maternity leave.
FAQ
How many weeks pregnant am I at embryo transfer?
At a day-5 blastocyst transfer, gestational age is counted as about 19 days (2 weeks and 5 days), because IVF dating adds the standard 14 days before fertilization. At a day-3 transfer it is about 17 days (2 weeks and 3 days). This "gestational age" is why you will already appear roughly two weeks pregnant on the day of transfer.
Why do I add 261 days for a blastocyst and 264 for a day-3 embryo?
A full-term pregnancy is counted as 280 gestational days from an imagined last period. A day-5 blastocyst has already completed 19 of those days by transfer, leaving 261. A day-3 embryo has completed 17, and IVF clinics conventionally quote the resulting EDD by adding 264 days. The exact stage your embryologist recorded is what makes the difference.
Does a frozen embryo transfer (FET) use the same calculation?
Yes. Whether the embryo was frozen and thawed or transferred fresh, the clock starts on the transfer date. Frozen day-5 blastocysts use the same 261-day rule, and frozen day-3 embryos use the same 264-day rule. The freezing itself does not change the due date.
How accurate is an IVF due date?
It is one of the most accurate due dates possible because the start of pregnancy is known precisely. Even so, only a minority of babies arrive exactly on their EDD; most healthy births happen within about two weeks before or after it. Your first-trimester ultrasound remains the clinical tie-breaker if measurements diverge.
What if my clinic used a day-6 blastocyst?
Enter stage 5 (261 days) for a day-6 blastocyst here, and confirm with your embryologist. Some clinics add one extra day for a slow-growing day-6 embryo, while others treat day-6 blastocysts identically to day-5. Because the discrepancy is small, ask the clinic which convention they used on your cycle summary.
Can my IVF due date change after the first ultrasound?
Sometimes. If your first-trimester ultrasound measures a crown-rump length that implies a gestational age more than five to seven days different from your transfer-based EDD, your doctor may update the date. After the first trimester, due dates are rarely changed.
Related Calculators
- Pregnancy Calculator — general pregnancy week and due-date tracker for natural conceptions.
- Due Date by Conception Calculator — back-calculate EDD from a known conception date.
- Conception Calculator — estimate your fertile window and likely conception date.
- Pregnancy Week Calculator — see which trimester and week you are in.
- Am I Pregnant? Calculator — early-signs guidance before a positive test.
Disclaimer
This IVF due date calculator is provided for informational purposes only and is not medical advice, nor a substitute for professional medical advice, diagnosis, or treatment. The estimate is based on standard IVF dating conventions and the transfer date and embryo stage you enter; actual delivery timing varies, and your fertility clinic and obstetrician determine your official estimated due date. Always confirm your EDD, gestational age, and any adjustments with your reproductive endocrinologist or prenatal care provider, and never delay medical care because of an estimate on this page. For editorial standards see the About page, and for data handling see the Privacy Policy.