How an IVF due date is calculated
In a natural pregnancy, conception is assumed to happen about 14 days after the last period starts, giving 266 days from conception to the due date. In IVF the moment of fertilisation is known, and the embryo is transferred when it is a known number of days old. The calculator therefore takes 266 days, subtracts the embryo’s age, and adds the result to your transfer date:
IVF due date = transfer date + (266 − embryo age in days)
| Starting date | Formula | Example: date = March 3 |
|---|---|---|
| Egg retrieval / insemination | + 266 days | November 24 |
| Day-3 embryo transfer | + 263 days | November 21 |
| Day-5 blastocyst transfer | + 261 days | November 19 |
| Day-6 blastocyst transfer | + 260 days | November 18 |
Your “weeks pregnant” after IVF
Even though there was no natural period, IVF pregnancies are counted in the same gestational weeks as any other pregnancy, so that growth charts and appointment schedules line up. The calculator works out an equivalent “last period” date 280 days before your due date. On the day of a day-5 transfer, for example, you are considered 2 weeks 5 days pregnant. Two weeks after transfer — around the time of the first blood test — you are about 4 weeks 5 days.
Why IVF due dates are rarely changed
Because the embryo’s age is known exactly, IVF dating is usually more precise than dating from a period or even an early scan, and due dates from IVF are generally kept even if later ultrasounds measure slightly ahead or behind. Your fertility clinic will confirm the due date it uses.
Day-3 vs. day-5 vs. day-6 transfer: why the due date changes
People are often surprised that two IVF pregnancies transferred on the same day can have due dates two or three days apart. The reason is the embryo’s age. A day-5 blastocyst is already two days further along than a day-3 embryo, so it reaches 40 weeks two days sooner. Here is the same transfer date with each embryo age:
| Transfer on June 10 | Days added | Estimated due date | Weeks pregnant on transfer day |
|---|---|---|---|
| Day-3 embryo | 263 | February 28 | 2 weeks 3 days |
| Day-5 blastocyst | 261 | February 26 | 2 weeks 5 days |
| Day-6 blastocyst | 260 | February 25 | 2 weeks 6 days |
(Dates assume the following year is not a leap year.) If your clinic dates the pregnancy from the egg retrieval or insemination date instead, choose that option in the calculator — it adds 266 days to the retrieval date, which gives the same result as counting from the transfer.
Turning IVF dates into a “last period” date
Prenatal care, growth charts and pregnancy apps all expect a first day of the last menstrual period (LMP). For an IVF pregnancy, that date is calculated rather than real:
Equivalent LMP = transfer date − (14 + embryo age) days
For a day-5 transfer on June 10, the equivalent LMP is June 10 − 19 days = May 22. Enter that date in any LMP-based tool — including the main Due Date Calculator — and you will get the same due date as the IVF method. The calculator above shows this equivalent date in your results so you can give it to your midwife or obstetrician.
Your IVF pregnancy timeline after transfer
Every clinic has its own schedule, but the early weeks of an IVF pregnancy commonly look like this (gestational age in brackets, for a day-5 transfer):
| Days after a day-5 transfer | Gestational age | What commonly happens |
|---|---|---|
| 0 | 2w 5d | Embryo transfer |
| about 9–11 | about 4w | First blood pregnancy test (beta hCG) |
| about 2–3 weeks | about 5–6w | Early ultrasound to check the pregnancy is in the uterus |
| about 3–4 weeks | about 6–7w | Ultrasound to look for a heartbeat |
| about 5–7 weeks | about 8–10w | Many people move from the fertility clinic to regular prenatal care |
| about 15–19 weeks | 18–22w | Detailed anatomy scan |
Use the Pregnancy Timeline to see every week of your pregnancy as calendar dates, starting from your IVF due date.
Days past transfer (DPT) in weeks pregnant
IVF communities often describe timing as “days past transfer” — for example 9dp5dt means nine days past a day-5 transfer. Gestational age on any DPT day is simply 14 days + the embryo’s age + the days since transfer:
| Days past transfer | Day-5 transfer | Day-3 transfer |
|---|---|---|
| 5 DPT | 3 weeks 3 days | 3 weeks 1 day |
| 7 DPT | 3 weeks 5 days | 3 weeks 3 days |
| 9 DPT | 4 weeks 0 days | 3 weeks 5 days |
| 11 DPT | 4 weeks 2 days | 4 weeks 0 days |
| 14 DPT | 4 weeks 5 days | 4 weeks 3 days |
This is the same “weeks pregnant” figure your clinic will use at the blood test and first scans, and it lines up exactly with the due date from the calculator.
Day-7 blastocysts and PGT-tested embryos
Some embryos develop more slowly and are biopsied or frozen on day 7. The rule is the same: subtract the embryo’s age from 266, so a day-7 blastocyst gives a due date 259 days after the transfer. Choose “Day-7 blastocyst” in the calculator. Embryos that have had preimplantation genetic testing (PGT) are dated exactly like any other embryo — the biopsy and the time spent frozen while results come back do not change the embryo’s developmental age, so they do not change the due date.
If you are unsure of your embryo’s age, your transfer report or clinic portal usually states it (for example “5AA blastocyst” or “day 6”). The first number in grades such as 5AA describes how expanded the blastocyst is, not its age in days, so check the day separately.
Fresh vs. frozen IVF transfers
For dating purposes there is no difference between a fresh and a frozen transfer: both use the embryo’s age at transfer (for frozen embryos, the age when they were frozen). What differs is how the transfer is timed — fresh transfers follow the egg retrieval, while frozen transfers happen in a later natural or medicated cycle. If you had a frozen transfer, the FET Due Date Calculator explains the equivalent last-period date for medicated cycles in more detail.
IUI and timed intercourse
Intrauterine insemination (IUI) and timed intercourse are not IVF: fertilisation happens inside the body, so there is no embryo age to enter. Use the insemination or ovulation date with the Conception Due Date Calculator, which adds 266 days. If your clinic monitored ovulation with a trigger shot, ovulation usually follows it by about a day and a half, so ask your clinic which date to use.
Planning around your IVF due date
Many IVF patients plan time off, travel and appointments around the due date. Useful tools: the Days Until Date countdown, Add Weeks to Date to find the date at any week of pregnancy, and the Days Between Dates calculator to count working days before leave begins. Keep in mind that birth anywhere from 37 to 42 weeks is considered within the normal range, so plan for the whole window rather than a single day.
IVF twins and the due date
If more than one embryo implants, the due date is calculated in exactly the same way — the formula does not change for twins. What does change is how likely an early birth is: twin pregnancies are, on average, delivered several weeks before the due date, and your care team will usually plan extra monitoring. Treat the due date as the 40-week reference point that all your scans and appointments are measured against.
What if my clinic’s due date is different?
A difference of a day is common and usually comes from how the clinic counts — some count the retrieval day as day 0, others as day 1, and some use the transfer date with a slightly different embryo age. Always use the date your clinic or care team gives you for medical purposes. Unlike pregnancies dated from a period, IVF due dates are generally not changed by later ultrasounds, because the start date is known precisely.
Donor eggs, embryo donation and frozen transfers
The same formula applies when donor eggs or donated embryos are used: what matters is the embryo’s age on the transfer date. For a frozen embryo transfer, the age to use is the age when the embryo was frozen (usually day 5 or 6) — the FET Due Date Calculator covers that case in detail. For IUI or timed intercourse, use the Conception Due Date Calculator with the date of insemination or ovulation.
Once you know your due date, the Pregnancy Timeline lays out every week of your pregnancy on the calendar, and the Days Until Date calculator gives you a countdown to your next appointment.