IVF transfer due date calculator

When transfer_date or embryo_age_days is missing or invalid, the task fails with invalid_input instead of inventing a date.

What the IVF transfer formula computes and why LMP is not required

Natural-cycle pregnancy dating usually starts from the first day of the last menstrual period and counts about two hundred eighty days to term. In IVF the conception moment is known through fertilization and culture, so obstetric dating is anchored to transfer instead of a possibly absent or irrelevant period date. The conventional length from conception to term is two hundred sixty-six days (thirty-eight weeks). If the embryo is already three days old at transfer, only two hundred sixty-three days remain after transfer; if it is a day-five blastocyst, two hundred sixty-one days remain. In general this endpoint implements EDD equals transfer_date plus two hundred sixty-six minus embryo_age_days with pure civil calendar arithmetic: it does not call Date.now, it does not depend on the server timezone, and it does not silently change embryo age. Required fields are transfer_date, an ISO calendar day written as YYYY-MM-DD naming the transfer, and embryo_age_days, a whole integer from zero through seven inclusive. The response also echoes normalized transfer_date and embryo_age_days, reports gestational_age_at_transfer_days as fourteen plus embryo age (the conventional LMP-equivalent gestational age at transfer), labels method as ivf_transfer, restates the formula, and lists human-readable steps so a UI can show the arithmetic without re-deriving it. This is a dating estimate only: it is not a diagnosis, not a guarantee of delivery on that day, and not a substitute for clinical ultrasound dating when that is available.

Input contract, validation, response shape, and deterministic errors

Month must fall between one and twelve; day must be real for that month, so values such as two thousand twenty-six February thirtieth are rejected. Do not send wall-clock timestamps, time zones, or LMP to this capability when you only need transfer-based IVF dating—those belong to other tools; this page is intentionally the transfer-plus-embryo-age formula only. POST a JSON object with required transfer_date as a string matching four digits, hyphen, two-digit month, hyphen, two-digit day, and required embryo_age_days as a whole integer from zero to seven. Aliases transfer, et_date, and embryo_transfer_date map to the date field; aliases embryo_day, day, and embryo_age map to the age field so forms can keep preferred names. Missing either required field, null, empty string, non-matching date strings, non-integer ages, and ages outside zero through seven all throw invalid_input naming the field and the expected shape. On success the body always includes transfer_date, embryo_age_days, due_date, days_added, gestational_age_at_transfer_days, method, formula, and steps; optional null fields are never padded in. Example: transfer_date two thousand twenty-six March fifteenth with embryo_age_days five yields days_added two hundred sixty-one and a due_date of two thousand twenty-six December first under the standard offset. Failed validation is not billed, so you can probe incomplete payloads without spending prepaid balance.

Where an IVF transfer due date API earns its keep in product and education

Fertility clinic portals and post-transfer care apps often need a first-pass estimated due date the moment the lab records transfer day and embryo stage, before any dating scan is uploaded. Embedding this calculator gives a transparent IVF baseline with a published formula and step list that nurses and product copy can quote without reverse-engineering a black-box date library. Prefer ultrasound-based dating when clinical policy requires it, and treat IVF transfer output as the conventional calendar estimate it has always been: simple, explainable, and deterministic.