Enter the embryo transfer date and the embryo's age at transfer. Works for fresh and frozen transfers.
| Milestone | Gestation | Date |
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An embryo of age n days at transfer was fertilised n days earlier. Gestational age counts from a notional last menstrual period 14 days before fertilisation, so:
Due date = transfer date + 266 − n days (e.g. +261 for Day 5, +263 for Day 3)
Gestational age = (date − transfer date) + n + 14 days
Scan windows follow NHS antenatal screening timings. This tool supports, and does not replace, clinical judgement.
Because the exact date of fertilisation is known, IVF dating is more precise than dating from a period. The calculator works back from the transfer date by the embryo's age to find the fertilisation date, then adds 266 days (38 weeks). For a Day 5 blastocyst that means the due date is 261 days after transfer; for a Day 3 embryo it is 263 days.
Pregnancy is conventionally counted from the first day of the last menstrual period (LMP), about two weeks before fertilisation. So on the day of a Day 5 transfer, the pregnancy is already counted as 2 weeks 5 days (2+5). The calculator shows the equivalent LMP so dates match those used by midwives and scan departments.
No. What matters is the embryo's age when it was transferred, not when it was created or how long it was frozen. Use the FET date and the embryo's developmental day (for example Day 5 or Day 6 blastocyst).
They are the number of days since fertilisation when the embryo was transferred. Day 2–3 embryos are at the cleavage stage; Day 5–6 (occasionally Day 7) embryos have reached the blastocyst stage. Your clinic's transfer notes will state the day.
It depends on where you have your maternity care. There is no clear national guidance on whether IVF pregnancies should keep the due date from the transfer date or be re-dated at the dating scan, so policy varies between local NHS trusts. Your maternity team will tell you which due date they will use.
The due date is an estimate. Only a small proportion of babies arrive on that exact day; most are born within two weeks either side. Term is from 37+0 weeks.
Clinics usually arrange a blood test around 9–11 days after a blastocyst transfer and a little later after a Day 3 transfer. The date shown in the table is a typical guide; always follow your clinic's instructions.
No. All calculations happen in your browser. Nothing you enter is saved or sent anywhere. We only count anonymous page visits, without cookies.
Scan timings: NHS fetal anomaly and combined screening programme (dating and combined screening 11+2 to 14+1 weeks; anomaly scan 18+0 to 20+6 weeks). Booking appointment and induction timing: NICE guidelines NG201 (Antenatal care) and NG207 (Inducing labour).