1) How to calculate your IVF EDD
Here is the rule that clears up D3 vs D5 in one line:
- EDD = transfer date + 266 days − embryo age in days.
- Day-5 embryo → add 261 days.
- Day-3 embryo → add 263 days.
Why? Standard gestation is counted from “gestational age,” which starts about two weeks before conception. With IVF, we know embryo age at transfer, so we back-solve from the known fertilisation timing.
Tip: If you prefer to think in weeks, 266 days ≈ 38 weeks from conception. Subtract the embryo’s age and you land at the same EDD you’d get from the LMP method.
2) Worked examples (so you can sanity-check)
-
Example A — Day-5 transfer
Transfer: 7 August 2025 (AEST).
EDD = 7 Aug 2025 + 261 days = 25 April 2026 (AEST). -
Example B — Day-3 transfer
Transfer: 7 August 2025 (AEST).
EDD = 7 Aug 2025 + 263 days = 27 April 2026 (AEST).
Use our IVF Due Date Calculator to avoid manual math and see week-by-week progress.
3) IVF vs LMP: why the numbers differ
LMP-based dates assume ovulation happened 14 days after your last period. That guess works for regular cycles conceived naturally. IVF uses a known fertilisation and embryo age, so the EDD comes from the transfer date and embryo day.
Clinics still confirm with an early ultrasound. If the first trimester scan differs meaningfully from your stated dates, most AU services follow the scan for accuracy. The due date should then stay fixed unless there is a strong reason to change it later.
4) Week-by-week milestones (typical)
These are common touchpoints. Your own clinic may time things slightly differently.
| Week (GA) | Milestone (typical in AU) |
|---|---|
| 6–9 weeks | Early dating/viability ultrasound; heartbeat often seen. |
| ≥10 weeks | NIPT (optional). Some choose this window. |
| 11–13+6 | First‑trimester combined screening window if used. |
| 18–20 weeks | Morphology (anomaly) scan. Standard AU timing. |
| 24 weeks | Threshold of viability; individual guidance varies. |
| 24–28 weeks | Glucose testing window is commonly here. |
| 28 weeks | If Rh‑negative, anti‑D is often given now (local protocols apply). |
| 35–37 weeks | Some services offer group B strep screening; practices vary in AU. |
| 40 weeks | EDD. Most babies arrive before or after this exact date. |
Use these as conversation starters, not as personal medical instructions.
5) Clinician-friendly summary (screenshot/print)
Patient: ___________________________
EDD (IVF): ____________________
Conception/IVF: Embryo transfer on [DD Month YYYY]; embryo age D3/D5.
EDD method: EDD = transfer date + 266 days − embryo age (D5 +261; D3 +263).
Planned early scan: [Week + day] at [clinic/service].
Notes: Any prior adjustments to EDD will be documented after the first trimester scan if indicated.
You can print this page or save to PDF. It helps everyone speak the same dating language.
6) How we calculate (short method note)
Our calculator applies the same rule you see above, with local date formatting for Australia and an AEST/AEDT note where relevant. For the detailed math and clinical sources, see Method & assumptions (planned).
7) Practical pointers
- If you had a frozen transfer, the math is the same. The embryo’s day at transfer drives the offset.
- Twins or higher-order multiples may change the timing of care. Your clinic will advise you.
- Once an EDD is set from an early scan, most services do not change it unless there is a strong clinical reason.
8) FAQs
Is IVF EDD more precise than LMP?
Why might a clinic change my date after ultrasound?
What about Day‑6 embryos?
Does FET vs fresh change the math?
Can I rely only on the calculator?
10) References
- Australian Clinical Practice Guidelines: Pregnancy Care (latest releases and living updates) — evidence-based antenatal care and dating practice in AU.
- ASUM guideline for first-trimester ultrasound — accurate dating and purposes of early scans.
- ACOG: Methods for Estimating the Due Date — framework for EDD and when to adjust.
- IVF-specific offsets explained (clinic resource) — Day-3 add 263 days; Day-5 add 261 days.