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How to Calculate Your IVF Due Date Accurately

Jan 13, 2026

An IVF pregnancy starts with something most pregnancies don’t have: a date you can point to with confidence.
You know when the embryo was created. You know when it was transferred. You know whether it was a Day 3 embryo or a Day 5 blastocyst. And yet, due dates still end up feeling strangely confusing—because every app asks for a last menstrual period (LMP) you may not even have, and different calculators can show different answers. Shape

Why IVF due dates are different (and why they’re often more accurate)

In a natural conception, doctors estimate gestational age from LMP because the exact fertilization date is unknown. IVF flips that.
With IVF, fertilization is timed and embryo age is known. That makes dating more precise—especially early on. The confusion usually comes from mixing IVF dates with LMP-style calculators.
If you remember only one thing: IVF due date calculations are not based on when you “missed a period.” They are based on embryo age and transfer date (or fertilization date). Shape

The simplest rule clinics use

Pregnancy is dated as 40 weeks (280 days) from LMP in the standard system. In that system, fertilization typically happens about 2 weeks (14 days) after LMP.
So in IVF, we “back-calculate” to match that same system.

IVF due date formula (transfer-date method)

Estimated Due Date (EDD) = Embryo Transfer Date + (266 − Embryo Age in Days) Because:

280 days (standard pregnancy length)
minus 14 days (the “pre-ovulation” part of the LMP system)
equals 266 days from fertilization
then adjust for the embryo’s age at transfer

This is the backbone of every reliable embryo transfer date calculator. Shape

IVF due date calculator shortcut table

Use this when you know your transfer date.

Embryo Stage at Transfer	Embryo Age	What to Add to Transfer Date
Day 3 embryo	3 days	263 days
Day 5 blastocyst	5 days	261 days
Day 6 blastocyst	6 days	260 days

So if you’re using an IVF pregnancy calculator, check whether it asks for embryo age or transfer day. If it doesn’t, it’s probably a generic calculator—and those are where the mismatches begin.
Read More: Pregnancy Calculator

Examples (so you can do it yourself in 30 seconds)

Example 1: Day 5 transfer

Embryo transfer date: August 10
Embryo age: 5 days
Due date: August 10 + 261 days

Example 2: Day 3 transfer

Embryo transfer date: August 10
Embryo age: 3 days
Due date: August 10 + 263 days

Same transfer date, different embryo age, different due date. That difference is not a mistake—it’s the point. Shape

If you know fertilization date (even easier)

Sometimes you have:

Egg retrieval date
Fertilization date (often the same day or the next day, depending on lab notes)

In that case:
EDD = Fertilization Date + 266 days
That’s why IVF dating is so steady: fertilization timing is not a guess.
ShapeRead More: All you need to know about IVF

Fresh vs Frozen transfer: does it change the due date?

No.
A frozen transfer changes timing on the calendar, not the embryo’s age. Due date calculations still depend on:

transfer date, and
embryo age on transfer day (Day 3/Day 5/Day 6)

So a frozen blastocyst transfer is still “Day 5” or “Day 6” for due date purposes.

Common mistakes that throw off IVF due date estimation

These are the usual reasons two calculators don’t match:

1) Using a regular pregnancy app that asks for LMP

If you enter an LMP that doesn’t align with IVF timing, the app will generate a different due date. IVF pregnancies often don’t map neatly onto LMP-based assumptions.

2) Confusing transfer date with conception date

Transfer day is not conception day. A Day 5 transfer means fertilization happened 5 days earlier.

3) Not knowing whether your embryo was Day 5 or Day 6

That one-day difference changes the due date by one day. Ask your clinic notes if you’re unsure.

4) Assuming twins change the due date

Twins change monitoring and delivery planning, not the calculation method. The dating method is the same.

What if your ultrasound due date differs from your IVF due date?

Early ultrasounds can shift dates in non-IVF pregnancies because conception timing is uncertain. In IVF, the conception timeline is known.
In most IVF cases, clinicians keep the IVF-based due date unless there’s a specific clinical reason to adjust (for example, measurement variation early on is common). The key is not the number on the screen—it’s consistent dating across your pregnancy for accurate growth monitoring.
If you’re seeing two different dates, the practical question is: Which date is your care team using for growth scans and milestones? That’s the one to anchor to.

Your quick “IVF due date calculator” checklist

To calculate accurately, you need only one of these:

Option A: Transfer date + embryo age

Transfer date
Day 3 or Day 5/6 embryo
→ Use the table above

Option B: Fertilization date

Fertilization date (or retrieval date if that’s how your clinic records it) → Add 266 days

Once you have the due date, everything else—week counts, trimester milestones, scan timing—becomes much simpler. Shape

Conclusion

A due date is not a prediction of the exact day your baby will arrive. It’s a clinical anchor—so your scans, growth tracking, and milestones stay consistent and meaningful.
With IVF, you don’t have to rely on guesswork or generic calculators. When you calculate using the embryo transfer date and embryo age, your due date is grounded in the most reliable information you have.
At BirthRight by Rainbow Hospitals, this is exactly how we approach IVF pregnancies: with clear dating, consistent monitoring, and guidance that keeps you informed—without adding unnecessary confusion to an already intense journey.

1) How accurate is an IVF due date calculator?

IVF due dates are typically more precise than natural conception estimates because the embryo’s age and transfer timing are known. The calculation is still an estimate (babies arrive on their own schedule), but the dating baseline is strong and clinically reliable.

2) How do I calculate my due date from embryo transfer date?

Use the transfer-date method:

Day 3 transfer: add 263 days to the transfer date
Day 5 transfer: add 261 days to the transfer date
Day 6 transfer: add 260 days to the transfer date
This is the logic used in an embryo transfer date calculator

3) Is IVF due date estimation based on LMP?

Not in the way most pregnancy apps use it. Many apps assume ovulation happens around Day 14 and back-calculate from LMP. IVF dating instead uses embryo age and transfer/fertilization timing. If an app forces an LMP entry, it can display a different date unless it’s an IVF-specific calculator.

4) Does the due date change for frozen embryo transfer (FET)?

No. Frozen vs fresh changes scheduling, not embryo age. IVF due date estimation still uses the embryo’s age on transfer day (Day 3/5/6) and your transfer date.

5) What’s the difference between conception date and embryo transfer date?

Conception (fertilization) occurs earlier than transfer. For example, with a Day 5 blastocyst transfer, fertilization happened about 5 days before the transfer date. Mixing these up is one of the most common reasons due date calculators disagree.

6) What if I don’t know whether my embryo was Day 5 or Day 6?

That one-day detail can shift the due date by a day. If you’re unsure, check your embryo transfer paperwork or ask your clinic—your lab notes will specify the embryo stage.

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How to Calculate Your IVF Due Date Accurately