The IVF due date formula
In a natural pregnancy the baby is born roughly 266 days after conception. With IVF, fertilisation happens in the lab on the day of egg retrieval (day 0), so we know the embryo’s exact age on transfer day. That gives a simple formula:
- Day 3 transfer: transfer date + 263 days
- Day 5 blastocyst: transfer date + 261 days
- Day 6 blastocyst: transfer date + 260 days
- Egg retrieval / IUI: retrieval or insemination date + 266 days
Quick reference table
| Transfer type | GA on transfer day | Days to due date |
|---|---|---|
| Day 3 embryo | 2w 3d | 263 |
| Day 5 blastocyst | 2w 5d | 261 |
| Day 6 blastocyst | 2w 6d | 260 |
When is the beta hCG test?
Most fertility clinics schedule a blood beta hCG test about 9–11 days after a day-5 transfer, or 11–12 days after a day-3 transfer. That lands around 4 weeks of gestational age. Home urine tests before this can be misleading – particularly because the “trigger” injection used before egg retrieval contains hCG and can cause a false positive for up to two weeks.
Always follow your own clinic’s protocol for beta hCG timing, progesterone support and when to stop medication. Never stop luteal-support medicines on the basis of a home test.
Fresh vs frozen transfer
For a frozen embryo transfer (FET) the date of freezing does not matter. What counts is the embryo’s developmental age when it is placed in the uterus. A day-5 blastocyst frozen two years ago and transferred today is still treated as a day-5 embryo today.
Why you’re already “2 weeks + embryo age” pregnant
To keep IVF pregnancies on the same scale as natural ones, clinics convert to an “LMP-equivalent” date – 14 days before fertilisation. So on the day of a day-5 transfer you are considered 2 weeks 5 days pregnant. This lets your obstetrician use the same scan charts and screening windows as for any other pregnancy.
After your first scan, you can follow your baby’s growth in our week-by-week guide. Expecting twins after transferring two embryos? Try the twin due date calculator.
Frequently asked questions
How do I calculate my due date after a day 5 transfer?
Add 261 days to the date of your day-5 blastocyst transfer. For example, a transfer on 1 March 2026 gives a due date of 17 November 2026.
How many weeks pregnant am I after a day 3 transfer?
On the day of a day-3 transfer you are 2 weeks 3 days pregnant. Add the days since transfer to find your current gestational age.
Is an IVF due date more accurate?
The starting point is much more precise, since fertilisation date is known. However, the natural spread in pregnancy length is the same as in any pregnancy, and IVF pregnancies – especially twins – have a higher chance of arriving early.
Does a frozen embryo transfer change the due date calculation?
No. The formula is the same; use the embryo’s age on the day of transfer.
When will I see the heartbeat after IVF?
A heartbeat is usually visible on a transvaginal scan at around 6–7 weeks of gestational age, which is roughly 3–4 weeks after a day-5 transfer.
Medical disclaimer: The results and information on this page are estimates for general education only. They are not a diagnosis and do not replace advice from your gynaecologist, obstetrician or midwife. If you have pain, bleeding, reduced baby movements or feel unwell, contact your doctor or call 108 immediately. Read the full disclaimer.
Sources & further reading
- American College of Obstetricians and Gynecologists (ACOG). Committee Opinion No. 700: Methods for Estimating the Due Date. acog.org
- Federation of Obstetric and Gynaecological Societies of India (FOGSI). Clinical practice recommendations. fogsi.org
- NHS (UK). Pregnancy tests; Ovulation; Your pregnancy and baby guide. nhs.uk