How does the ivf due date calculator work?
- An embryo transferred on day 5 is already 5 days past fertilisation. Due date = transfer date + 266 days - 5, so +261.
- Day-3 transfer: +263 days. Day-6 transfer: +260 days. From egg collection (or IUI): +266 days.
- Weeks pregnant are then counted the usual way, as if from a last period 2 weeks before fertilisation.
- Clinics usually set a blood test about 9 to 11 days after a day-5 transfer. We show the rough window, but your clinic's date is the one to use.
Why IVF dates are so precise
With IVF the day of fertilisation is known, so there's no guessing about ovulation. Your clinic will still date the pregnancy by scan, usually from about 6 to 7 weeks. If you need support through treatment, the HFEA has independent information, and our guide on looking after your mind may help.
When to see a doctor
- Follow your clinic's test date and scan plan.
- Symptoms of OHSS: bloating, tummy pain, breathlessness, being sick. Call your clinic.
- Bleeding or one-sided pain after a positive test.
In the UK you can call NHS 111 for advice, any time. In an emergency call 999 (UK) or 911 (US).
Questions people ask
How is an IVF due date calculated?
From the embryo's age. A day-5 blastocyst transfer adds 261 days; a day-3 transfer adds 263 (ACOG).
How many weeks pregnant am I at transfer?
About 2 weeks plus the embryo's age: 2+5 at a day-5 transfer, 2+3 at a day-3 transfer.
Is a frozen embryo transfer different?
No. Use the transfer date and the embryo's age at freezing, just like a fresh transfer.
When can I test after transfer?
Your clinic will give you a date, often about 9 to 11 days after a day-5 transfer. Testing earlier at home can mislead, especially if you had a trigger injection.
Is anything I enter saved or sent?
No. Everything runs in your browser. Nothing is stored or sent, and the page makes no network requests when you use it.
Sources
Written by the Splash team · Sources checked Oct 2026 · Updated
