5-Day Blastocyst Transfer Due Date Calculation

Day 5 Transfer: Key Facts

What is a Day 5 Blastocyst?

To understand day 5 due date calculations, it helps to know what a blastocyst is and why day 5 is significant in embryo development.

After an egg is fertilized (day 0), it begins dividing:

• Day 1: The fertilized egg (zygote) has two pronuclei visible
• Day 2: 2-4 cells
• Day 3: 6-8 cells (cleavage stage embryo)
• Day 4: Morula stage (cells compact together)
• Day 5: Blastocyst stage (100+ cells, distinct structures form)

A blastocyst is an embryo that has developed for five days and reached a critical milestone. At this stage, the embryo has differentiated into two distinct cell types:

• Inner cell mass (ICM): These cells will become the baby
• Trophectoderm: These outer cells will become the placenta

The embryo also develops a fluid-filled cavity called the blastocoel. A blastocyst typically contains 100-200 cells, compared to just 6-8 cells at day 3.

Why Day 5 Transfers Are Most Common

Day 5 blastocyst transfers have become the standard of care in IVF for several important reasons:

1. Natural Selection

Not all fertilized eggs have the potential to become babies. By growing embryos to day 5, the lab can identify which embryos are truly viable. Many embryos that look normal at day 3 will fail to develop to the blastocyst stage, indicating they likely wouldn't have resulted in pregnancy anyway.

2. Better Embryo Selection

Blastocysts are easier to grade and assess for quality. Embryologists can evaluate the inner cell mass, trophectoderm, and expansion level to select the embryo most likely to implant.

3. Improved Synchronization

In natural conception, embryos reach the uterus at approximately the blastocyst stage. Transferring a day 5 embryo better mimics the natural timing, as the uterine environment is optimally prepared for a blastocyst rather than a cleavage-stage embryo.

4. Higher Success Rates

Studies consistently show that day 5 transfers have higher implantation and pregnancy rates per transfer compared to day 3 transfers. This is primarily due to better embryo selection rather than an inherent advantage of the blastocyst stage itself.

5. Enables Single Embryo Transfer

Because blastocyst transfer success rates are higher, clinics can confidently transfer a single embryo, reducing the risk of twins and higher-order multiples while maintaining good pregnancy rates.

The Day 5 Transfer Due Date Formula

Now let's get to the calculation. For a day 5 blastocyst transfer, here's the exact formula:

Due Date = Transfer Date + 261 days

Or equivalently: Due Date = Transfer Date + 37 weeks + 2 days

Where Does 261 Days Come From?

A full-term pregnancy is 40 weeks, or 280 days, from the first day of the last menstrual period (LMP). At the time of a day 5 transfer, your gestational age is already:

• 14 days (standard time from LMP to ovulation in pregnancy dating) + 5 days (embryo age) = 19 days

So you need the remaining days to reach 280:

280 - 19 = 261 days

This means on the day of your day 5 transfer, you are already 2 weeks and 5 days pregnant according to standard medical dating.

Day 5 Transfer Due Date: Detailed Examples

Example 1: January Transfer

You have a day 5 blastocyst transfer on January 15, 2026.

Calculation:

1. Start date: January 15, 2026
2. Add 261 days
3. January has 31 days, so 31 - 15 = 16 days remaining in January
4. 261 - 16 = 245 days remaining after January
5. February: 28 days (245 - 28 = 217)
6. March: 31 days (217 - 31 = 186)
7. April: 30 days (186 - 30 = 156)
8. May: 31 days (156 - 31 = 125)
9. June: 30 days (125 - 30 = 95)
10. July: 31 days (95 - 31 = 64)
11. August: 31 days (64 - 31 = 33)
12. September: 30 days (33 - 30 = 3)
13. October: 3 days = October 3

Due date: October 3, 2026

Example 2: Summer Transfer

Day 5 transfer on June 20, 2026.

Quick calculation: June 20 + 261 days = March 8, 2027

Example 3: Fall Transfer

Day 5 transfer on September 1, 2026.

Quick calculation: September 1 + 261 days = May 20, 2027

Calculating Your Theoretical LMP

Many medical forms and pregnancy apps ask for your last menstrual period date. Since you may not have had a natural period before your IVF cycle, you need to calculate a "theoretical LMP" that gives you the correct gestational dating.

For a day 5 transfer:

Theoretical LMP = Transfer Date - 19 days

LMP Examples

• Transfer on January 15, 2026 → LMP: December 27, 2025
• Transfer on June 20, 2026 → LMP: June 1, 2026
• Transfer on September 1, 2026 → LMP: August 13, 2026

When you enter this theoretical LMP into a standard pregnancy calculator or app, it will correctly calculate your due date and gestational age.

Day 5 Transfer Gestational Age Timeline

Here's what your gestational age looks like at key points after a day 5 transfer:

Day 5 vs. Day 3 vs. Day 6: Comparing Due Dates

The embryo age at transfer directly affects your due date calculation. Here's how day 5 compares to other transfer days:

As you can see, transferring an older embryo results in a slightly earlier due date. This makes sense because the embryo is further along in development at the time of transfer.

Day 5 Blastocyst Grading Reference

Blastocysts are graded using a three-part system: expansion number (1-6), inner cell mass grade (A-C), and trophectoderm grade (A-C). For example, "4AA" means expansion level 4, grade A inner cell mass, grade A trophectoderm. Here is a complete reference:

Important: The expansion stage and grade do not change your due date calculation. Whether your day 5 embryo was graded 3BB or 5AA, you still use the same formula (transfer date + 261 days).

Implantation Rates by Embryo Grade

Embryo quality does affect your chance of pregnancy, though not the due date itself. Here are approximate implantation rates by blastocyst grade:

These are general estimates. Individual outcomes depend on many factors including patient age, uterine receptivity, and whether PGT-A testing was performed.

Day 3 vs. Day 5 vs. Day 6: Pros and Cons

Day 5 Transfer: Month-by-Month Quick Reference

Use this table to quickly estimate your due date based on your day 5 transfer month (assuming transfer on the 1st of each month):

Day 5 Transfer with Assisted Hatching

Some embryos receive assisted hatching, where the embryologist creates a small opening in the zona pellucida (outer shell) to help the embryo hatch and implant. This procedure does not change the due date calculation—the embryo is still a day 5 blastocyst regardless of assisted hatching.

Day 5 Fresh vs. Frozen Transfer

Whether your day 5 embryo was transferred fresh (during your stimulation cycle) or after being frozen and thawed (FET), the due date calculation is identical:

• Fresh day 5 transfer: Transfer date + 261 days = Due date
• Frozen day 5 transfer: Transfer date + 261 days = Due date

The freezing and thawing process doesn't change the embryo's developmental age. A day 5 blastocyst that was frozen for a year is still a day 5 embryo when thawed and transferred.

Early Pregnancy After Day 5 Transfer

Understanding the timeline after your day 5 transfer helps manage expectations:

Days 1-4: Implantation Window

The blastocyst hatches from its shell and begins implanting into the uterine lining. This process takes several days.

Days 5-9: hCG Production Begins

Once implanted, the embryo starts producing hCG (human chorionic gonadotropin). Levels are initially very low.

Days 9-14: Beta hCG Test

Most clinics schedule blood tests 9-14 days post-transfer. A positive result confirms pregnancy. Many clinics repeat the test 2-3 days later to ensure hCG is rising appropriately (should roughly double every 48-72 hours).

Weeks 6-7: First Ultrasound

At approximately 6-7 weeks gestational age (3-4 weeks after a day 5 transfer), you'll have your first ultrasound. This confirms the pregnancy is in the uterus and may detect a heartbeat.

Day 5 Transfer Success Rates

Day 5 blastocyst transfers typically have higher success rates than day 3 transfers. However, success depends on many factors:

• Patient age
• Embryo quality (grading)
• Uterine receptivity
• Whether embryos were tested (PGT-A)
• Fresh vs. frozen transfer
• Previous pregnancy history

While success rates don't affect due date calculation, higher-quality day 5 blastocysts are associated with better outcomes.

Common Day 5 Transfer Questions

My embryo was a "5AA"—does the grade affect my due date?

No. Embryo grades (like 5AA, 4BB, etc.) describe quality and developmental stage but don't change the due date calculation. A 5AA embryo and a 3BB embryo transferred on the same day 5 have the same due date formula.

I had two day 5 embryos transferred. Does this change my due date?

No. Whether you transferred one or multiple embryos, the due date calculation is the same. If both embryos implant (resulting in twins), your delivery will likely be earlier than the calculated due date, but that's a separate consideration.

My clinic said my embryo was "slow" and didn't reach blastocyst until day 6. What date do I use?

Use the day the embryo was actually transferred. If it reached blastocyst on day 6 and was transferred on day 6, use the day 6 formula (260 days). If it was then frozen and transferred later as a "day 6 blastocyst," still use day 6.

Is 261 days exactly 9 months?

Close, but not exactly. 261 days is about 8 months and 3 weeks. The "9 months" of pregnancy is an approximation—the actual duration from conception to due date is about 38 weeks (266 days), but we measure from LMP, which adds roughly 2 weeks.

Using Our Day 5 Transfer Calculator

Skip the math entirely with our IVF Due Date Calculator:

1. Enter your transfer date
2. Select "Day 5 (Blastocyst)"
3. Choose fresh or frozen
4. Click Calculate

You'll instantly see your:

• Estimated due date
• Current gestational age (weeks and days)
• Trimester
• Progress percentage
• Pregnancy milestones with dates
• Days until due date

Summary

The day 5 blastocyst transfer is the gold standard in modern IVF, offering the best combination of embryo selection and pregnancy success rates. Calculating your due date is straightforward:

• Formula: Transfer date + 261 days = Due date
• Gestational age at transfer: 2 weeks, 5 days (19 days)
• Theoretical LMP: Transfer date - 19 days

This formula works for both fresh and frozen day 5 transfers, regardless of embryo grade or whether assisted hatching was performed. For quick, accurate calculations, use our free IVF Due Date Calculator and get your complete pregnancy timeline in seconds.