FET Due Date Calculator

Estimated due date —

Due date (written out): —
Gestational age on check date: —
Days until due date: —
Trimester on check date: —
Equivalent last period start: —
Days added to transfer date: —
Share of 40 weeks reached: —

Progress toward 40 weeks on the check date

The chart appears with your result

After a frozen embryo transfer, the due date is the transfer date plus 266 days minus the embryo's age in days. A day-5 blastocyst transferred on 10 January 2026 gives 261 days and a due date of 28 September 2026. Freezing time does not count, because the embryo does not develop while stored.

About this tool

Frozen embryo transfer pregnancies have a known start point, so the due date does not rest on a remembered period or a variable ovulation day. This calculator takes the thaw-and-transfer date, the embryo's stage when it was frozen, and a second date you choose for checking progress. It returns the estimated due date, the gestational age on the check date in weeks and days, the trimester, the days still to go and the equivalent last-period date that clinics and apps often ask for. A progress bar shows how far through 40 weeks the pregnancy is on that day. The dates follow the obstetric convention, which counts two weeks before conception, so a pregnancy is already about 3 weeks along on transfer day. The result is an estimate; your fertility clinic or a first-trimester scan sets the date used in your notes.

How to use it

Enter the transfer date
Use the day the thawed embryo was placed, not the day it was frozen or the start of the medicated cycle.
Pick the embryo age
Choose Day 3, Day 5 or Day 6 as recorded by the embryology lab when the embryo was vitrified.
Set a check date
Enter today or an appointment date to see gestational age, trimester and days remaining on that day.
Read the working
The steps list each day count, so you can trace how the due date and weeks were reached.

Examples

Day-5 blastocyst thawed and transferred on 10 January 2026

Frozen embryo transfer date: 2026-01-10
Embryo age when frozen: Day 5
Check progress on: 2026-02-07

Result Estimated due date: 2026-09-28
Due date (written out): September 28, 2026
Gestational age on check date: 6 weeks 5 days
Days until due date: 233
Trimester on check date: First trimester
Equivalent last period start: 2025-12-22
Days added to transfer date: 261
Share of 40 weeks reached: 16.8%

Days from transfer to due date = 266 − 5 = 261
Due date = 2026-01-10 + 261 days = 2026-09-28
Days since transfer on 2026-02-07 = 28
Gestational age = 14 + 5 + 28 = 47 days
Days to due date = 280 − 47 = 233

Adding 261 days gives 28 September. Four weeks after transfer, on the usual first-scan window, the pregnancy dates to 6 weeks 5 days.

Day-3 embryo transferred on 2 March 2026

Frozen embryo transfer date: 2026-03-02
Embryo age when frozen: Day 3
Check progress on: 2026-03-02

Result Estimated due date: 2026-11-20
Due date (written out): November 20, 2026
Gestational age on check date: 2 weeks 3 days
Days until due date: 263
Trimester on check date: First trimester
Equivalent last period start: 2026-02-13
Days added to transfer date: 263
Share of 40 weeks reached: 6.1%

Days from transfer to due date = 266 − 3 = 263
Due date = 2026-03-02 + 263 days = 2026-11-20
Days since transfer on 2026-03-02 = 0
Gestational age = 14 + 3 + 0 = 17 days
Days to due date = 280 − 17 = 263

A cleavage-stage embryo is two days younger than a blastocyst, so 263 days are added and the due date lands on 20 November.

How it is calculated

Due date = T + (266 − A); gestational age on C = 14 + A + (C − T) days

T: Frozen embryo transfer date
A: Embryo age at freezing, in days (3, 5 or 6)
C: Check date chosen for the progress reading
266: Average days from conception to birth (280 minus 14)

ACOG Committee Opinion 700 dates assisted-reproduction pregnancies from the embryo's age and transfer date. A pregnancy is counted as 280 days from a notional last period, with conception at day 14. An embryo of age A is treated as conceived A days before transfer, so 266 − A days remain. Time in the freezer is ignored, since development stops during vitrification. Gestational age on the check date adds the days elapsed since transfer to 14 + A.

Sources

Methods for Estimating the Due Date (Committee Opinion 700) — American College of Obstetricians and Gynecologists

When not to use it

Once a first-trimester ultrasound has dated the pregnancy, your clinic may keep the transfer date or note a scan date instead.
It does not date pregnancies from intrauterine insemination or natural cycles, which need an ovulation or period date.
It does not predict the actual day of labour for twins, where earlier delivery is common.

Common mistakes

Entering the date the embryo was frozen instead of the date it was thawed and transferred.
Using the day of the medicated cycle or progesterone start as the embryo age.
Adding the years an embryo spent in storage to the pregnancy length.

Frequently asked questions

Does the time my embryo spent frozen change the due date?

No. Vitrification pauses development, so an embryo frozen at day 5 is still a day-5 embryo when it is thawed years later. Only its stage and the transfer date matter for dating.

Why does the calculator say I am already about 3 weeks pregnant on transfer day?

Obstetric dating starts from a notional last period two weeks before conception. A day-5 blastocyst on transfer day is treated as 14 + 5 = 19 days along, which is 2 weeks 5 days. This keeps FET pregnancies on the same scale as every other pregnancy chart and scan report.

How many days are added for each embryo age?

266 minus the embryo age: 263 days for a day-3 embryo, 261 for a day-5 blastocyst and 260 for a day-6 blastocyst. The tool shows the number it used in the stats and the steps.

Is a frozen transfer due date different from a fresh IVF due date?

The arithmetic is the same. In both cases the transfer date and the embryo's age give the conception-equivalent date. What differs is the cycle around it, for example a medicated or natural endometrial preparation, which does not change the dating.

What does the equivalent last period date mean?

It is the date a last menstrual period would have started for a natural pregnancy of the same age: transfer date minus 14 days minus the embryo age. Some apps and forms ask for an LMP, and this value lines them up with the clinic's dating.

Will my baby actually arrive on this date?

Rarely on the day itself. The date marks 40 weeks 0 days, and ACOG treats 39 weeks 0 days to 40 weeks 6 days as full term. Most births fall within a couple of weeks either side.

Can I use a check date in the future?

Yes. Enter a planned scan or appointment date to see the gestational age and trimester you will be at on that day, up to 300 days after transfer.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 19). FET Due Date Calculator. Tools Directory. Retrieved October 28, 2026, from https://tools.milunir.com/health/pregnancy-and-fertility/fet-due-date-calculator/

MLA

Tools Directory Editorial Team. “FET Due Date Calculator.” Tools Directory, 19 Oct. 2026, https://tools.milunir.com/health/pregnancy-and-fertility/fet-due-date-calculator/. Accessed 28 Oct. 2026.

Chicago

Tools Directory Editorial Team. “FET Due Date Calculator.” Tools Directory. Last modified October 19, 2026. Accessed October 28, 2026. https://tools.milunir.com/health/pregnancy-and-fertility/fet-due-date-calculator/.

Link

<a href="https://tools.milunir.com/health/pregnancy-and-fertility/fet-due-date-calculator/">FET Due Date Calculator – Tools Directory</a>