Enter the embryo transfer date and the embryo's age at transfer. Works for fresh and frozen transfers.
| Milestone | Gestation | Date |
|---|
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
This follows ACOG guidance that IVF pregnancies are dated using the embryo's age and the transfer date1. Scan and appointment timings follow NHS and NICE guidance2,3,4. This tool supports, and does not replace, clinical judgement.
Because the date of fertilisation is known, IVF pregnancies are dated from the embryo transfer rather than from a period.1 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 the due date is 261 days after transfer; for a Day 3 embryo it is 263 days.7
By convention, pregnancy is counted from the first day of the last menstrual period (LMP), about two weeks before fertilisation, with the due date 280 days after that.1 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.1,7 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. NICE recommends a dating scan at 11+2 to 14+1 weeks for all pregnancies3, while US guidance advises keeping the IVF-derived date.1 There is no clear national UK guidance on which to use for IVF pregnancies, 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. A pregnancy is considered full term from 37+0 weeks6, and induction of labour is usually discussed from 41+0 weeks.5
Your clinic will give you a test and a date to use it, usually around 16 days after the embryo transfer. Testing earlier can give a false result, so use the date you are given.2
No. All calculations happen in your browser. Nothing you enter is saved or sent anywhere. We only count anonymous page visits, without cookies.