Due Date from a Blastocyst Transfer or Ovulation Date: Counting Weeks After IVF

Due date from ovulation: ovulation date + 266 days

In pregnancy weeks, the day of ovulation and fertilization is treated as "2 weeks 0 days". The due date is 40 weeks 0 days, so from ovulation to the due date is 38 weeks, or 266 days. If you ovulated on August 17, 2026, the due date is 266 days later, on May 10, 2027.

You can use this calculation if you know your ovulation date from timed intercourse, or if you became pregnant through intrauterine insemination (IUI). Because IUI is timed to ovulation, the procedure date is usually counted as the ovulation date. An ovulation date estimated from basal body temperature or ovulation tests has a margin of one or two days, so that much error remains.

Due date from the transfer date: the days to add depend on the embryo's age

With IVF and ICSI, the egg retrieval date (the day of fertilization) is counted as 2 weeks 0 days, the same as an ovulation date. Embryos are cultured for a few days after retrieval before being returned to the uterus, so the transfer date is "2 weeks 0 days + the embryo's age in days". For a blastocyst (day-5 embryo) the transfer date is 2 weeks 5 days, and for an early-stage embryo (day-3 embryo) it's 2 weeks 3 days.

Even with transfers on the same day, the longer the embryo has been growing, the earlier the due date. A day-5 blastocyst and a day-3 early-stage embryo differ by two days. Check which day your embryo was from the paperwork given at transfer or your culture records.

Counting for a frozen embryo transfer

The calculation works the same way for a frozen embryo transfer, where a frozen embryo is thawed and returned. The time it spent frozen isn't counted, and you use the embryo's age when it was frozen. For a blastocyst frozen on day 5, the transfer date is 2 weeks 5 days and the due date is the transfer date + 261 days.

• Even if the retrieval cycle and the transfer cycle differ, count from the transfer date, not the retrieval date
• In a hormone replacement cycle transfer, don't use your last period date either (because ovulation is controlled with medication, a calculation from your last period won't fit)
• A due date from the transfer date is accurate, so it's often not revised much at the early-pregnancy ultrasound. Ultimately, follow the due date set by your clinic

A guide to the weeks after transfer

Counting weeks from the transfer date tells you which week the test day and appointments fall in. If you transferred a blastocyst (day-5 embryo) on September 1, 2026, 0 weeks 0 days is August 13, 2026, and from then on every Thursday is "X weeks 0 days".

How many days after transfer the pregnancy blood test is done, and when you move ("graduate") to a regular maternity clinic, vary by clinic. For later milestones such as the heartbeat check, the stable period and the final month, see Pregnancy schedule by week.

Why it's better not to calculate from your last period after IVF

Calculating the due date from your last period rests on the assumption that you ovulated on day 14 after it. With IVF, the retrieval and transfer dates are adjusted with medication, so that assumption simply doesn't apply.

• Fresh embryo transfer: ovarian stimulation changes how the follicles grow, and the retrieval date isn't necessarily day 14 after your last period
• Frozen embryo transfer (hormone replacement cycle): the uterine lining is prepared with medication before transfer, so which day after your last period the transfer falls on varies by cycle
• Frozen embryo transfer (natural cycle): the transfer is timed to your own ovulation, but the embryo's age is as it was when frozen. Counting from the transfer date, where both the ovulation date and the embryo's age are known, is more reliable

For example, in a hormone replacement cycle where a blastocyst is transferred 20 days after the start of the last period, calculating from the last period puts the transfer day at 2 weeks 6 days, while counting from the transfer date puts it at 2 weeks 5 days. In this example the gap is just one day, but the further the transfer is from the last period, the bigger the gap, and the weeks stop matching what you're told at checkups. If you became pregnant through IVF, use the transfer date rather than your last period as the reference.

Calculating from a transfer or ovulation date with the tool

1. 1

   Choose the basis for the calculation

   Under "What do you want to calculate from?" in the Due Date & Pregnancy Week Calculator, choose "Ovulation date" or "Embryo transfer date".

2. 2

   Enter the date and the embryo's age

   For an embryo transfer date, enter the day of transfer and choose the embryo type: day-2 embryo, day-3 embryo (early-stage), day-5 embryo (blastocyst) or day-6 embryo (blastocyst).

3. 3

   Check the due date and today's week

   It shows the due date, today's pregnancy week and the date that counts as 0 weeks 0 days. You can also check each week's dates in the Pregnancy week calendar tab.

When you switch the basis, the date in the input field is replaced while keeping the same pregnancy. For example, if you calculate from the embryo transfer date and then switch to "From due date", the due date field is filled in with the calculated due date. How to think about calculating from your last period is explained in How to calculate your due date.

FAQ

Which pregnancy week is the day of a blastocyst transfer?

For a day-5 blastocyst, the transfer day is 2 weeks 5 days pregnant; for a day-6 blastocyst, 2 weeks 6 days. For a day-3 early-stage embryo, it's 2 weeks 3 days. The retrieval date (the day of fertilization) is counted as 2 weeks 0 days, and the days the embryo was cultured are added.

How do I calculate the due date after a blastocyst transfer?

For a day-5 blastocyst, the due date is the transfer date plus 261 days. With a transfer on September 1, 2026, the due date is May 20, 2027. For a day-3 early-stage embryo, add 263 days for May 22, 2027.

Is the calculation the same for a frozen embryo transfer?

Yes. The time spent frozen isn't counted. Use the embryo's age when frozen (5 days for a day-5 blastocyst) and calculate from the transfer date. Neither the retrieval date nor your last period is used.

After IUI, what is the due date calculated from?

The usual approach is to treat the IUI date as the ovulation date and add 266 days. If the IUI was on August 17, 2026, the due date is May 10, 2027. Pregnancy weeks are counted with 14 days before the procedure as 0 weeks 0 days.