IVF dating guide
How IVF due dates are calculated
IVF pregnancy dating starts with the actual embryo transfer date and the embryo’s clinic-confirmed developmental age. A Day-5 transfer uses the transfer date plus 261 days; a Day-3 transfer uses the transfer date plus 263 days.
The same rule applies to a fresh or frozen embryo transfer (FET) when the clinic records a supported Day-3 or Day-5 age. If your fertility or prenatal care team has established an estimated due date (EDD), use that recorded date for care.
Day 3, Day 5 and the due-date formula
Use the actual transfer date and the embryo age documented by the clinic. For the two transfer records supported here, Day 5 means adding 261 days and Day 3 means adding 263 days. Day 3 and Day 5 describe the embryo’s developmental age recorded for transfer, not days since transfer or embryo quality.
Do not substitute the egg-retrieval, freezing, thawing, implantation, or pregnancy-test date for the completed transfer date. If the transfer has not occurred yet, treat a scheduled date only as planning information and use the completed clinic record afterward.
| Transfer type | Pregnancy age on transfer day | Due-date rule |
|---|---|---|
| Day-3 embryo | 2w3d | Transfer date + 263 days |
| Day-5 blastocyst | 2w5d | Transfer date + 261 days |
The Day-3 offset is two days longer because a Day-3 embryo is two developmental days younger than a Day-5 embryo at transfer. Both rules place the pregnancy on the same conventional obstetric calendar.
Example: transfer date March 1, 2024
- Day-5 transfer: March 1 + 261 days = estimated due date November 17, 2024.
- Day-3 transfer: March 1 + 263 days = estimated due date November 19, 2024.
These are calendar calculations, not predictions of implantation, treatment success, or the actual day of birth.
Obstetric pregnancy dating includes 14 conventional days before fertilization. A Day-3 embryo therefore begins transfer day at 14 + 3 = 17 pregnancy-calendar days, or 2 weeks, 3 days (2w3d). A Day-5 embryo begins at 14 + 5 = 19 days, or 2 weeks, 5 days (2w5d). Those two weeks are a dating convention, not two weeks of embryo development or proof that a menstrual period occurred.
Fresh and frozen embryo transfers (FET)
A fresh transfer uses an embryo without prior cryopreservation. A frozen embryo transfer uses an embryo that was frozen and later warmed or thawed before transfer. Dating still starts from the actual transfer date and the clinic-confirmed total developmental age for that transfer.
Do not use the egg-retrieval, freezing, thawing, or pregnancy-test date in place of the transfer date, and do not add culture days yourself. If the clinic confirms Day 3 or Day 5, the calculator supports that record; otherwise use the clinic’s EDD or ask which developmental age was used.
Intracytoplasmic sperm injection (ICSI) changes the fertilization technique, not the Day-3 or Day-5 transfer dating rule. Donor egg, donor embryo, or gestational-carrier status also does not change these day-count offsets.
Which record should I use?
Use the current EDD documented by your fertility or prenatal care team for care. Do not average several IVF due dates, repeatedly recalculate to choose a preferred one, or replace an established clinic date with an online estimate.
If you want to see how many weeks pregnant you are on another date, use the Gestational Age Calculator with the current recorded EDD. Ultrasound remains clinically important, but an online calculator cannot decide whether a discrepancy should change an established date.
Pregnancy Metrics supports only documented Day-3 and Day-5 embryo transfers. If the record says Day 2, Day 4, Day 6, Day 7, another age, an unknown age, or conflicting ages, do not select the nearest option. Use the clinic-established EDD or ask the clinic which developmental age and due date apply to this pregnancy.
Why estimates differ and what they cannot tell you
Two estimates can differ when they use different embryo ages, the wrong treatment date, a planned rather than completed transfer, or an older record rather than the current clinic EDD. A frozen-cycle calculation can also be wrong if someone tries to reconstruct developmental age instead of using the clinic-confirmed total age.
Check the actual transfer date and recorded embryo age, then follow the current date in the pregnancy record. The calculation should clarify the record, not compete with it.
The calculator can apply the published Day-3 or Day-5 calendar offset and show the resulting estimated due date and pregnancy-calendar age. It cannot determine:
- implantation or pregnancy success;
- viability or pregnancy location;
- hCG progression or fetal wellbeing;
- medication or treatment decisions; or
- the exact date of birth.
Official sources
- ACOG — Methods for Estimating the Due Date — Supports ART-based dating and the 261-day Day-5 and 263-day Day-3 transfer offsets.
- ASRM — The International Glossary on Infertility and Fertility Care, 2025 — Defines ART dating and terminology for embryo development, transfer, and frozen-thawed cycles.
- CDC — ART Glossary of Terms — Defines embryo transfer, fresh and frozen embryo cycles, gestational age in ART, and ICSI.
- MedlinePlus — In Vitro Fertilization — Explains the major steps in IVF, including embryo culture, transfer, implantation, and pregnancy testing.
- HFEA — Decisions to Make About Your Embryos — Provides embryo-stage context for cleavage-stage and blastocyst-stage transfers.
These organizations provide the cited definitions and dating guidance. They do not review, certify, sponsor, or endorse Pregnancy Metrics.