IVF due date calculator

Why IVF dating is different — and better

Every other way of estimating a due date is an inference. Counting 280 days from a last period assumes you remember the date, that your cycle is 28 days, and that you ovulated on day 14. Measuring an embryo on a scan assumes it is growing at the population average. IVF assumes nothing: the eggs were collected on a known day, fertilised in a laboratory on that day, and the embryo was graded and transferred on a numbered day after that. The date of conception is a logged event.

That precision has a practical consequence. Because the dates are exact, they are not revised by a later scan. As one NHS trust states in its patient leaflet: "For IVF pregnancies dates are not changed based on scan measurements and the due dates given by the IVF clinic are adhered to." If your 12-week scan measures a few days out, your dates stay as they are. That is the opposite of what happens in a spontaneous pregnancy, where an early scan normally overrides a remembered period.

Working from the transfer date

Take your transfer date and add 266 days, then subtract the age of the embryo. The subtraction is the whole trick: a day-5 blastocyst had already been alive for five days when it was put back, so five days of the pregnancy had already elapsed before the transfer. A day-3 embryo had used three. This is why a day-3 and a day-5 transfer from the same egg retrieval produce the same due date — they should, because they are the same pregnancy, dated from the same day 0.

ACOG Committee Opinion 700 is the authority most often cited here, and it gives the two common numbers directly rather than leaving them to be derived. The general formula, covering day 2 through day 6 and frozen as well as fresh cycles, appears in hospital operating procedures such as the Royal Hospital for Women's in Sydney.

Working from the egg retrieval date

If you know the retrieval date but not the transfer date — common if you had a freeze-all cycle and are looking back, or if you are estimating before a transfer is booked — add 266 days to the retrieval date. Retrieval day is treated as equivalent to day 14 of a 28-day cycle, which is why the same 266 that applies to a known conception date applies here.

The gestational age that does not match your calendar

On the day of your day-5 transfer, this calculator will tell you that you are 2 weeks and 5 days pregnant. Nothing has been implanted yet and the embryo is five days old. Both things are true, because gestational age is measured from a notional last menstrual period two weeks before conception. Every professional body uses this convention, so a "7-week scan" means the same thing for an IVF pregnancy as for any other — but it does mean that the number of weeks you are told will always run about two weeks ahead of the age of your embryo. It is worth knowing before someone says it to you in a waiting room.

What the timeline is for

The dated timeline below the result exists because IVF pregnancies come with more appointments and more waiting than most, and the waiting is easier when it has dates attached. The blood pregnancy test (beta hCG) window is anchored to your transfer or retrieval date, because that is how clinics book it — typically 9 to 14 days after transfer, though your clinic's own date always wins. Everything after that is anchored to gestational age, because that is how the rest of maternity care is organised.

The gestational sac usually becomes visible on a transvaginal scan around 5 weeks, and a fetal heartbeat is usually detectable from about 6 weeks; most clinics book the first viability scan between 6 and 8 weeks. Around 8 weeks the embryonic period ends and many fertility clinics discharge patients to routine maternity care. Cell-free DNA screening becomes available from 10 weeks. The NHS offers a dating scan at 11 to 14 weeks — which, for you, will confirm rather than change your dates — and the detailed 20-week screening scan between 18 and 21 weeks. RANZCOG's guidance in New Zealand recommends the first scan ideally between 12 and 13+6 weeks. The first trimester ends at 13+6, the second at 27+6.

What a due date does not promise

Precise dating does not mean a precise birth date. Knowing the day of conception to the hour tells you nothing about how long labour will take to start. The NHS states that pregnancy normally lasts 37 to 42 weeks, and the research is blunter still: Jukic and colleagues, writing in Human Reproduction in 2013, note that only about 4% of women deliver at 280 days and only 70% within 10 days either side of the estimated date. Their study of pregnancies with hormonally confirmed ovulation found term gestation ranged across 37 days. Treat the date as the centre of a five-week window.

Two things this calculator cannot do. It cannot account for twins, which are common after IVF and are rarely carried to 40 weeks — a twin pregnancy is dated the same way but managed on a different schedule. And it is not a substitute for your clinic. Your embryology report has the embryo day on it; if you are unsure whether yours was a day-5 or a day-6 blastocyst, ask, because it is a one-day difference and it is the only input here that can be wrong.