IVF Due Date Calculator
Enter your embryo transfer date and embryo age to calculate your estimated due date and current gestational age.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter a transfer date and click Calculate.
For general information only — your clinic dating is the authority.
How the IVF due date calculation works
Unlike natural conception — where the exact moment of fertilisation is never known — IVF gives you a precise date and time. This makes the pregnancy dating significantly more accurate for IVF pregnancies than for spontaneous ones.
The formula is straightforward: your due date is the transfer date plus a fixed number of days that depends on the age of the embryo at transfer.
Day-5 blastocyst transfer
Due date = transfer date + 261 days (37 weeks 2 days)
The embryo has already developed for 5 days, so less time needs to be added.
Day-3 cleavage-stage transfer
Due date = transfer date + 263 days (37 weeks 4 days)
The younger embryo needs an extra 2 days to reach the same developmental point.
Where do these numbers come from?
Standard pregnancy dating counts 280 days (40 weeks) from the last menstrual period (LMP). In IVF, we know the exact fertilisation date. A Day-5 embryo is already 5 days old, so: 280 − 5 − 14 = 261 days from transfer. A Day-3 embryo is 3 days old, so: 280 − 3 − 14 = 263 days from transfer. The 14 subtracted in both cases represents the two weeks before ovulation (the follicular phase) that is included in the 280-day LMP convention.
Understanding gestational age
Gestational age is how far along the pregnancy is, measured in weeks and days. It starts counting from the first day of the last menstrual period (LMP) by convention — not from fertilisation. This is why gestational age is always about two weeks ahead of the actual embryonic age.
For IVF pregnancies gestational age is calculated as:
For example, if your Day-5 transfer was 100 days ago, your gestational age would be 100 + 5 + 14 = 119 days, which is exactly 17 weeks.
Worked example
Scenario: Day-5 blastocyst transfer on 1 June 2026.
Scenario: Day-3 cleavage-stage transfer on 15 August 2026.
Who should use this calculator
IVF patients
Get an immediate estimate of your due date and how far along you are, from the one date you know for sure — your embryo transfer.
Fertility clinic staff
Use the calculator as a quick reference when counselling patients about their expected due date and pregnancy timeline.
Partners and family
Plan maternity leave, announce dates, and prepare for the baby's arrival with a reliable due-date estimate based on the clinical facts.
Researchers & educators
Demonstrate how IVF dating differs from natural conception dating, and illustrate the gestational-age formula for medical trainees.
Tips for using your IVF due date
Your clinic ultrasound is the authority
While the calculated date is very accurate for IVF pregnancies, your clinic's first-trimester ultrasound (usually at 6–8 weeks) is the gold standard for confirming and potentially adjusting your due date. The ultrasound measures the crown–rump length (CRL), which correlates closely with gestational age in early pregnancy.
Day 3 vs Day 5 matters
Always use the correct embryo age. A Day-3 transfer adds 263 days; a Day-5 transfer adds 261 days. Using the wrong setting shifts your due date by two days, which can affect scheduling around the 40-week mark.
Track your gestational age milestones
Use the calculator throughout your pregnancy to see your current gestational age. Each trimester brings different milestones — viability, anatomy scan, third-trimester growth scans — and knowing your exact week helps you stay informed and prepared.
Share the date with your clinic
When you first contact your clinic after a positive pregnancy test, they will ask for your transfer date and embryo age. Having your calculated due date ready can make the intake conversation smoother.
The formulas in full
Day-5 blastocyst due date
dueDate.setDate(dueDate.getDate() + 261)
Equivalent to: transfer date + 37 weeks + 2 days
Day-3 cleavage-stage due date
dueDate.setDate(dueDate.getDate() + 263)
Equivalent to: transfer date + 37 weeks + 4 days
Gestational age
const gestationalDays = daysSinceTransfer + embryoAge + 14
const weeks = Math.floor(gestationalDays / 7)
const days = Math.round(gestationalDays % 7)
The 14 accounts for the two weeks before ovulation in standard pregnancy dating. At transfer, gestational age is already 2 weeks + embryo age in days.
Why IVF dating is more precise
In natural conception, the due date is usually estimated from the first day of the last menstrual period (LMP) or from an early ultrasound. But women ovulate on different cycle days, sperm can survive for several days, and fertilisation itself is invisible. The LMP method assumes a 28-day cycle with ovulation on day 14 — which doesn't fit many women.
With IVF, every variable is controlled and documented. The egg is retrieved at a known time, fertilised in the lab, and transferred on a specific date. The embryologist records whether the embryo was transferred on day 3 (cleavage stage, ~6–8 cells) or day 5 (blastocyst, ~100–200 cells). That exact knowledge makes IVF due-date calculation more reliable than LMP-based dating for natural pregnancies.
Studies have shown that IVF-dated pregnancies have fewer "post-term" inductions because the dating is simply more accurate. That said, nature still has its own timeline — only about 4–5% of babies are born exactly on their due date, whether conceived naturally or through IVF.
Important limitations
- This calculator gives an estimate, not a medical diagnosis.
- Your clinic's ultrasound dating — especially the first-trimester scan — is the authoritative due date.
- Multiple pregnancies (twins, triplets) often deliver earlier than the calculated due date.
- Individual factors such as maternal age, health conditions, and previous pregnancy history can affect delivery timing.
- Frozen embryo transfers use the same formula — the freeze/thaw process does not change the gestational age calculation.
- Donor egg and embryo transfers follow the same logic: use the transfer date and embryo age at transfer.
Related tools
Frequently asked questions
Why is IVF dating more precise?
The conception timing is known exactly from the transfer, unlike natural conception where the exact day of ovulation and fertilisation is uncertain.
Day 3 vs Day 5 — does it matter?
Yes — a Day-3 transfer adds 263 days (about 37 weeks 4 days), while a Day-5 transfer adds 261 days (about 37 weeks 2 days). The two-day difference shifts your estimated due date.
Is this my official due date?
Treat it as an estimate; your clinic ultrasound will confirm or adjust the date, especially the first-trimester scan which is the most accurate for dating.
How is gestational age calculated?
Gestational age = (today — transfer date) + embryo age in days + 14 days. The extra 14 days accounts for the two weeks before ovulation (the follicular phase) in standard pregnancy dating.
Sources & references
This tool uses standard formulas and reference values from:
- • NIH / National Institutes of Health and CDC reference values and formulas. nih.gov
- • Peer-reviewed equations (e.g. Mifflin-St Jeor, Harris-Benedict) as originally published.
- • ACOG for pregnancy, ovulation and due-date methodology. acog.org
Not medical advice. Estimates only — consult a qualified healthcare professional for any personal health decision.