How a frozen embryo transfer due date works
A frozen embryo is effectively paused in time. Whether it was frozen last month or several years ago, its developmental age is the age it was when it was frozen — usually day 5 or day 6 for a blastocyst, sometimes day 3. After thawing and transfer, it continues from that age. So the formula for an FET due date is the same as for a fresh IVF transfer:
FET due date = transfer date + (266 − embryo age at freezing)
For the most common case, a day-5 blastocyst, that is the transfer date + 261 days. A day-6 blastocyst is + 260 days and a day-3 embryo + 263 days. The year the embryo was created does not change the due date at all.
Medicated and natural FET cycles
Frozen transfers are timed in one of two ways. In a medicated (programmed) cycle, estrogen and progesterone prepare the uterine lining and the transfer is scheduled after a set number of days of progesterone. In a natural or modified-natural cycle, the clinic tracks your own ovulation and times the transfer to it. Either way, it is the transfer date and embryo age that set the due date — so you do not need your period date at all.
Clinics still describe the pregnancy in gestational weeks, counted from an equivalent “last period” that the calculator shows in your results (280 days before the due date). On the day of a day-5 FET you are 2 weeks 5 days pregnant; your first beta blood test about 9–11 days later typically falls at around 4 weeks.
FET example: day-5 vs. day-6 blastocyst
| Frozen transfer on August 12, 2026 | Estimated due date | Equivalent last period |
|---|---|---|
| Day-5 blastocyst (+261 days) | April 30, 2027 | July 24, 2026 |
| Day-6 blastocyst (+260 days) | April 29, 2027 | July 23, 2026 |
The equivalent last-period date is what your prenatal care team will use to describe the pregnancy in weeks. It is calculated as the transfer date minus 14 days minus the embryo’s age, so it does not depend on when (or whether) you actually had a period in a medicated cycle.
Why FET due dates can differ by a day from your clinic
Clinics sometimes count embryo age slightly differently — for example by treating the thaw day or the day of fertilisation as day 0 or day 1. A difference of one day is normal and not significant. Use the date your clinic gives you for appointments; once set, an FET due date is generally not changed by later scans because the embryo’s age is known.
Your FET pregnancy calendar
The result above includes a milestone calendar — end of the first trimester, the anatomy-scan window, full term and the due date — so you can plan the months ahead. For a week-by-week layout, open the Pregnancy Timeline; for fresh IVF cycles or retrieval-date dating, use the IVF Due Date Calculator.