How IVF due dates are calculated

Use the actual embryo transfer date and the embryo day recorded by the fertility clinic.

• Day-5 blastocyst transfer: estimated due date = transfer date + 261 days.
• Day-3 embryo transfer: estimated due date = transfer date + 263 days.
• Pregnancy age on transfer day: 2 weeks, 5 days for Day 5; 2 weeks, 3 days for Day 3.

ACOG recommends using ART-derived gestational age to assign the estimated due date when a pregnancy results from assisted reproductive technology. For IVF, the embryo age and transfer date are the key dating records.

The result is an estimated due date and pregnancy timeline. It is not confirmation that implantation or pregnancy occurred.

In a naturally conceived pregnancy, the exact fertilization date usually is not observed. Pregnancy dating therefore often begins with the last menstrual period or an early ultrasound.

IVF provides a different kind of record. Fertilization or ICSI occurs in the laboratory, the embryo develops for a documented number of days, and the embryo is transferred on a known date.

ACOG states that when pregnancy results from ART, the ART-derived gestational age should be used to assign the due date. The age of the embryo and the date of transfer place the pregnancy on the standard obstetric calendar.

That is why a transfer-based IVF due date should not be replaced with an ordinary last-period estimate when the treatment record is available.

Day 3 and Day 5 describe the embryo’s developmental age in the clinic record, not the number of days since transfer.

The HFEA describes cleavage-stage embryos as embryos selected on day two or three of development and blastocyst-stage embryos as embryos selected on day five. The 2025 international infertility glossary notes that the blastocyst stage typically begins on day five or six.

The embryo-day label should come from the clinic record. It is not a judgment about embryo quality, genetic status, or likelihood of success.

For a documented Day-5 blastocyst transfer:

Estimated due date = embryo transfer date + 261 days

The 261-day interval accounts for the embryo already being five days old at transfer while preserving the standard 266-day interval from fertilization to the estimated due date.

Worked example

The pregnancy age on March 1 is 2 weeks, 5 days. The calculated pregnancy-dating start is February 11, 2024—19 days before transfer.

That calculated start is a calendar reference. It does not claim that an actual menstrual period began on February 11.

For a documented Day-3 embryo transfer:

Estimated due date = embryo transfer date + 263 days

The 263-day interval is two days longer than the Day-5 formula because the embryo is two days younger at transfer.

Worked example

The pregnancy age on March 1 is 2 weeks, 3 days. The calculated pregnancy-dating start is February 13, 2024—17 days before transfer.

Again, this is an obstetric dating reference, not evidence of an actual last menstrual period.

Obstetric gestational age begins about two weeks before fertilization in the standard pregnancy calendar.

The 2025 international infertility glossary states that, for ART, gestational age is calculated by adding 14 days to the completed time since in vitro insemination or ICSI.

For the two supported transfer types:

• Day 3 after fertilization + 14 days = 17 gestational days, or 2 weeks, 3 days.
• Day 5 after fertilization + 14 days = 19 gestational days, or 2 weeks, 5 days.

This does not mean the embryo has existed for two extra weeks. The extra 14 days belong to the pregnancy-dating convention.

Once the transfer-day pregnancy age is established, pregnancy age on a later date is calculated by adding the number of calendar days since transfer.

Gestational days on the selected date = gestational days at transfer + days since transfer

Worked example

A Day-5 transfer occurred on March 1, 2024.

• Pregnancy age on transfer day: 2 weeks, 5 days = 19 gestational days.
• March 15 is 14 days after March 1.
• 19 + 14 = 33 gestational days.
• 33 days = 4 weeks, 5 days.

The same March 15 reference date after a Day-3 transfer on March 1 would be 4 weeks, 3 days.

Checking another date changes only the displayed pregnancy age. It does not change the due date.

A fresh embryo transfer uses an embryo that has not previously been cryopreserved. A frozen embryo transfer, or FET, uses an embryo that was frozen and later thawed or warmed for transfer. CDC defines these as separate ART cycle types.

For a standard documented Day-3 or Day-5 transfer, both fresh and frozen transfers use:

• the actual transfer date, and
• the embryo age recorded for that transfer.

Do not use the original egg retrieval date as the transfer date in a frozen cycle. The retrieval may have occurred months or years earlier.

The 2025 international infertility glossary explains that FET gestational age reflects the embryo’s combined culture time before freezing and after thawing. If the record describes an embryo age other than Day 3 or Day 5, or includes additional post-thaw culture that makes the embryo-day label unclear, use the due date assigned by the clinic rather than guessing.

These events belong to the same treatment process, but they are not interchangeable dating inputs:

MedlinePlus describes IVF as a sequence that includes egg retrieval, insemination or ICSI, embryo culture, and embryo transfer. It also explains that pregnancy depends on an embryo implanting after transfer.

Do not enter the retrieval date, pregnancy-test date, or an assumed implantation date into a transfer-date field.

A scheduled transfer date can produce a planning estimate.

That estimate can show:

• the due date that would follow from the scheduled date and embryo age;
• the pregnancy age that would be assigned on the scheduled transfer day; and
• later calendar milestones if the transfer occurs as planned and results in pregnancy.

It cannot confirm that:

• the planned embryo will be available for transfer;
• the transfer will occur on that date;
• implantation will occur;
• a pregnancy test will be positive; or
• the pregnancy will continue.

Use the completed transfer record as the authoritative input after the procedure.

No. ICSI changes how fertilization is attempted in the laboratory, not how the resulting ART pregnancy is placed on the obstetric calendar.

CDC defines ICSI as injection of a single sperm directly into an egg. The 2025 international glossary applies the same 14-day gestational-age convention after either in vitro insemination or ICSI.

For a documented Day-3 or Day-5 transfer after ICSI, use the same transfer-date formula.

The formula does not assess whether fertilization was normal, whether an embryo is euploid, or whether ICSI was clinically indicated.

The calendar formula still follows the embryo age and transfer date.

The genetic source of the egg or sperm does not change:

• the number of days in the obstetric dating convention;
• the pregnancy age assigned on transfer day; or
• the Day-3 and Day-5 transfer offsets.

CDC includes donor egg cycles, donated embryo cycles, and gestational carrier cycles within ART terminology.

The result does not identify genetic parentage, legal parentage, embryo ownership, or any treatment outcome.

Pregnancy Metrics currently supports only:

• documented Day-3 embryo transfers; and
• documented Day-5 blastocyst transfers.

Do not force another record into one of those options.

Examples that require the clinic’s documented due date or clarification include:

• a Day-2, Day-4, Day-6, or Day-7 transfer;
• an embryo with additional post-thaw culture;
• a record that lists only “cleavage stage” or “blastocyst” without a day;
• a transfer record with conflicting embryo-age information;
• a transfer involving embryos of different recorded ages.

The 2025 international glossary recognizes embryo transfer at stages from day one through day seven and notes that blastocyst development can begin on day five or six and may be delayed to day seven.

Use the clinic’s established due date when the record falls outside the calculator’s supported inputs.

Common reasons include:

1. One calculation used Day 3 and another used Day 5.
2. The transfer date was entered incorrectly.
3. A retrieval date was used instead of the actual frozen-transfer date.
4. The original freezing day was used without accounting for post-thaw culture.
5. A scheduled date was entered, but the completed transfer occurred on another date.
6. An ordinary last-period calculator was used instead of the ART record.
7. One date came from an old treatment note and another from the current pregnancy record.
8. The clinic established or corrected the due date using more complete treatment information.

Do not average several due dates.

Use the current estimated due date documented by the fertility clinic or prenatal care team.

ACOG identifies first-trimester ultrasound, through 13 weeks and 6 days, as the most accurate ultrasound method to establish or confirm gestational age. ACOG also states that ART-derived gestational age should be used when assigning the due date after IVF.

An early ultrasound can assess the developing pregnancy and help the care team review the timeline. It does not replace the need to use the correct embryo age and transfer record.

Once the due date is established, ACOG recommends that later changes be reserved for rare circumstances and documented. ACOG’s obstetric data definitions likewise state that a pregnancy should not be redated by a later ultrasound after the best obstetric EDD has been established.

An online calculator cannot decide whether a discrepancy requires clinical review or redating.

The two-day difference reflects embryo age at transfer. It does not rank the embryos or compare treatment success.

• Use the IVF Due Date Calculator when you have a documented Day-3 or Day-5 embryo transfer date.
• Use the Gestational Age Calculator when the clinic has already established a due date and you want pregnancy weeks and days on a selected date.
• Use the Pregnancy Due Date Calculator for a non-ART estimate from a last period, well-supported ovulation date, or documented fertilization date.
• Use the Conception Date Calculator only for a general calendar estimate from a due date, last period, or dated pregnancy-weeks record. It does not reconstruct an IVF laboratory timeline.

An IVF due-date estimate cannot determine:

• whether an embryo implanted;
• whether a biochemical or clinical pregnancy occurred;
• pregnancy location;
• pregnancy viability;
• fetal cardiac activity;
• embryo quality;
• chromosome status;
• treatment success;
• live-birth probability;
• the number of fetuses;
• fetal growth or wellbeing;
• medication timing;
• whether treatment should be changed or stopped;
• the cause or urgency of symptoms;
• whether a due date should be revised; or
• the exact day of birth.

Do not use this page to decide when to test, stop progesterone or other medication, change treatment, or delay urgent care.

Follow the fertility clinic’s instructions and seek qualified medical care for symptoms or concerns.

1. ACOG — Methods for Estimating the Due Date

   States that ART-derived gestational age should be used to assign the estimated due date; gives 261 days from transfer for a Day-5 embryo and 263 days for a Day-3 embryo; identifies first-trimester ultrasound as the most accurate ultrasound dating method; and recommends that later due-date changes be uncommon and documented. The document is marked reaffirmed in 2025.

2. ASRM — The International Glossary on Infertility and Fertility Care, 2025

   Defines ART gestational age by adding 14 days to time since in vitro insemination or ICSI; explains how estimated insemination timing is derived for frozen-thawed embryo transfer cycles; and defines embryo stages, embryo transfer, fresh transfer, and frozen-thawed transfer terminology.

3. CDC — ART Glossary of Terms

   Defines embryo transfer, fresh and frozen embryo cycles, gestational age in ART, ICSI, donor cycles, and gestational carriers.

4. MedlinePlus — In Vitro Fertilization

   Describes the sequence of egg retrieval, insemination or ICSI, embryo culture, embryo transfer, implantation, and pregnancy testing.

5. HFEA — Decisions to Make About Your Embryos

   Distinguishes cleavage-stage embryos commonly selected on day two or three from blastocyst-stage embryos selected on day five.

6. ACOG — reVITALize Obstetrics Data Definitions

   Defines the best estimated due date using the strongest obstetric information, including known fertilization dates from ART, and states that later ultrasound should not redate a pregnancy after the best obstetric EDD has been established.

These sources do not endorse Pregnancy Metrics.

Pregnancy Metrics provides educational calendar estimates only. This page does not confirm transfer completion, implantation, pregnancy, pregnancy location, viability, fetal growth, treatment success, or the exact day of birth. Use the due date, embryo record, medication instructions, and follow-up plan established by your fertility clinic or prenatal care team.