IVF Due Date Calculator

The one pregnancy where the dates are not a guess

Every other due date calculator on this site is, underneath, making an estimate about something nobody watched. It takes the date of your last period and assumes you ovulated on day 14, assumes the sperm and egg met promptly, and assumes your memory of the date is right. Reasonable assumptions. Still assumptions.

IVF is different, and it is worth appreciating how different. Somebody was in the room. The fertilisation happened in a lab, on a known date, at a known hour. The embryo was cultured for a known number of days and transferred on a known date. There is no ovulation to guess at, no cycle length to average, no remembered period to misremember. Of all the pregnancies there are, yours is the one with the paperwork.

That precision is why the professional guidance says that when assisted reproduction is involved, the dating derived from the treatment should be used to set the due date, rather than working backwards from a period. Below is the arithmetic that does it, the thing about your gestational age that confuses nearly everyone after IVF, the one input mistake worth avoiding, and what multiples do and do not change.

The arithmetic: 266 minus the embryo's age

Start from one fact: a pregnancy runs about 266 days from fertilisation. That is the same 266 days that sits under every conception-based due date, IVF or not.

Now the IVF twist. When your embryo was transferred, it had already been alive for a few days in the lab. Those days count. A day-5 blastocyst has already used up five of its 266. So the sum is simply:

Due date = transfer date + (266 − embryo age in days)

Which produces the numbers this tool uses:

The pattern extends if your clinic did something less common. A day-6 blastocyst would be 266 minus 6, so 260 days. A day-2 transfer would be 264. You are always just subtracting the embryo's birthday-in-the-lab from 266.

A day-5 transfer, worked through

Suppose your blastocyst went in on 15 March 2026. It was a day-5 embryo, so:

Days to add = 266 − 5 = 261
Due date = 15 March 2026 + 261 days = 1 December 2026

Worth seeing how little the transfer type moves things. Same 15 March transfer, run as a day-3 embryo, gives 3 December. Run from a retrieval date instead, at 266 days, it gives 6 December. So the whole spread across every option is five days. Getting the transfer type wrong will not wreck your planning, but getting it right costs you nothing.

You were already two weeks pregnant at transfer

This is the part that makes IVF patients stare at their notes. You walk into a clinic not pregnant, have a five-minute procedure, and walk out officially two weeks and five days pregnant. Nothing has had time to happen. Yet the number is correct.

The reason is the convention that runs all of obstetrics: gestational age is counted from the first day of a last menstrual period, roughly two weeks before conception. Everyone gets those two free weeks, IVF or not. Our How Many Weeks Pregnant Am I page covers why that convention exists.

For IVF, there was no meaningful last period to count from, so the clock is reconstructed: 14 days of notional pre-ovulatory time, plus however old the embryo already was.

So when a midwife later asks how many weeks you are and the answer feels two weeks ahead of the biology, it is. It is ahead for everybody. IVF just makes the arithmetic visible instead of hiding it inside a guess about ovulation.

Transfer date or retrieval date? They are not the same

This is the single most common input error, and it is an easy one to make, because both dates are sitting on the same discharge letter and neither is labelled helpfully.

Your retrieval is the day the eggs were collected and fertilised. Your transfer is the day the embryo went back, typically three to six days later. They are different dates, and they belong to different formulas: 266 days from the retrieval, or 266 minus the embryo age from the transfer. Mix them up and your due date moves by several days.

One quirk of this tool worth knowing. The day-3 and day-5 options work from your transfer date, as labelled. The two options for own eggs and donor eggs add the full 266 days, which is the arithmetic for a fertilisation or retrieval date, not a transfer date. So if you know your embryo's age, pick the day-3 or day-5 option and enter the transfer date, and you will get the cleanest answer. If your clinic gave you a retrieval date and no embryo age, that is when the 266-day option is the one you want.

When in doubt, your clinic's own letter usually states an estimated due date. That is the one to trust, and this page is a way of understanding where it came from.

Fresh or frozen changes nothing

People are routinely surprised by this one, particularly if their embryo spent two years in storage. A frozen embryo transfer uses exactly the same formula as a fresh one.

The reason is that the freezing does not age the embryo. Development stops when it is frozen and resumes when it is thawed. A day-5 blastocyst frozen in 2024 and transferred in 2026 is still, developmentally, a five-day-old embryo on transfer day. Time in the tank is not time in the pregnancy. So a frozen day-5 transfer is transfer date plus 261, same as a fresh one, and whether your cycle was medicated or natural makes no difference either.

Twins, triplets, and why your due date does not move

This trips people up because two true things sound like they contradict each other.

The first: your due date does not change for multiples. It is still 40 weeks, still the same arithmetic from the same transfer date. The embryos were the same age; the calendar does not care how many of them there were. That 40-week date stays your official estimated date on the notes.

The second: multiples almost always arrive earlier anyway. Twins commonly come around 37 weeks, triplets around 33. That is not a different due date, it is a different reality, and your team will plan around it with closer monitoring and a delivery conversation well before 40 weeks.

So the honest way to hold it is that the due date is the reference point, not the prediction. If you are expecting twins, the tool will still give you the 40-week date and note that twins tend to come early, which is the correct way round. Expect to meet them before the date on the chart.

Planning it backwards from a date you want

The tool has a second mode, for people who have not transferred yet and are trying to work out timing. Pick a target birth date and it runs the sum in reverse to tell you when the transfer would need to happen.

Say you would like to give birth on 25 December 2026 with a day-5 transfer. Subtract 261 days and the transfer lands on 8 April 2026.

A dose of realism about this, though, because IVF is not a train timetable. Cycles get delayed for ordinary reasons: response to stimulation, lining thickness, embryos that do not make it to day 5, a freeze-all decision, a clinic's schedule. And even with a perfect transfer date, only a small share of babies arrive on their due date at all. Treat this mode as a rough guide to which month you would be aiming at, useful for a conversation with your clinic rather than a plan you build around.

Does an IVF due date still need a scan?

Yes, and this is a nice reversal of how dating usually works.

In a natural pregnancy, an early ultrasound routinely overrules the period-based due date, because measuring the embryo beats guessing at ovulation. In IVF, the dating is already precise, so the scan is not there to correct your date. It is there to confirm the pregnancy is progressing, check where it has implanted, and find out how many are in there, which matters rather a lot if two embryos were transferred or one decided to split.

So expect an early scan, and do not be alarmed if a measurement comes back a few days off your calculated date. Early scans carry their own margin of about five to seven days. With IVF, your transfer date is the better information, and your clinic will generally keep the date the arithmetic gave.

Where the estimate still has slack

Precise dating does not mean a precise birthday, and it is worth separating the two:

• The date is precise; the birth is not. Knowing exactly when your pregnancy started tells you nothing about when labour will begin. Only around 4 to 5 percent of babies arrive on their due date, IVF included.
• Anything from 37 to 42 weeks is normal. Hold the date as a window rather than an appointment.
• Multiples shift the realistic date, not the calculated one. See above.
• This is arithmetic, not care. Your clinic's date, and your notes, outrank this page. If they disagree, go with your clinic.

Questions people ask

If my day-5 transfer was on 15 March 2026, when is my due date?

1 December 2026. That is 15 March plus 261 days, which is 266 days of pregnancy minus the 5 days your blastocyst had already lived in the lab. On transfer day you were already 2 weeks and 5 days pregnant by standard counting.

Is the due date different for a frozen embryo transfer?

No. Same formula, same result. What matters is how old the embryo was when it was transferred, not how long it was frozen or whether the cycle was medicated. A frozen day-5 blastocyst is transfer date plus 261, exactly like a fresh one.

Is an IVF due date more accurate than a normal one?

The dating is, yes, and by a good margin. A standard due date rests on a remembered period and an assumed day-14 ovulation, which is why roughly 40 percent of women get redated after an early scan. Your date rests on a lab record. That said, accurate dating does not make labour punctual, so the spread of possible birthdays is the same as anyone else's.

Should I use an earlier due date because I am having twins?

No, keep the 40-week date, since that is what your notes will use. But plan your life around arriving earlier, because twins commonly come around 37 weeks and triplets around 33. Your team will be watching closely and will talk timing with you well before the calculated date.

What if my embryo was a day-6 or day-2 transfer?

Same rule, different subtraction: 266 minus the embryo's age. A day-6 blastocyst gives transfer plus 260, and a day-2 embryo gives transfer plus 264. This tool offers the two common options, day-3 and day-5, so for anything else do the sum by hand or use your clinic's date.

My form asks for an LMP but I did IVF. What do I write?

A very common headache with medicated cycles, where there may not have been a real period at all. The usual answer is a notional last period 14 days before fertilisation, so about 19 days before a day-5 transfer or 17 days before a day-3. Your clinic can give you the exact date they are using, and it is worth asking for it once and writing it down, since you will be asked repeatedly.

References

Where the figures come from. The recommendation that dating derived from assisted reproduction should be used to set the due date, the accuracy of first-trimester ultrasound, and the redating figures quoted above come from the ACOG committee opinion on estimating the due date. The 266-day interval from fertilisation, the 280-day convention it derives from, and the point that only around 4 percent of babies arrive on the estimated date draw on the Medscape review of gestational assessment.

1. American College of Obstetricians and Gynecologists. Methods for estimating the due date. Committee Opinion No. 700. Obstetrics & Gynecology. 2017;129:e150-e154. acog.org
2. Evaluation of Gestation. Medscape Reference. https://emedicine.medscape.com/article/259269-overview