Gestational age from due date calculator

Invalid calendars, ages before estimated LMP, and ages beyond forty-two weeks return a clear invalid_input error and are not charged.

How gestational age is derived from an estimated due date

This calculator performs that integer identity with proleptic Gregorian serial day counts: each ISO date is validated as a real calendar day (including leap years), converted with the well-known days_from_civil mapping, and combined without floating-point day fractions, network lookups, or the host clock. On success you receive the normalized edd and as_of strings, the term_days assumption, estimated_lmp, gestational_days as a non-negative integer, weeks and days remainder, a human gestational_age string such as "18 weeks + 1 days", days_until_edd (negative when past due), trimester as one, two, or three using common clinical cut-points at thirteen and twenty-eight completed weeks, is_post_term when gestational days exceed the chosen term, and a short formula reminder.

Inputs, aliases, term length, and error contract

Both must be real Gregorian days in YYYY-MM-DD form with years from one through nine thousand nine hundred ninety-nine; impossible days such as twenty twenty-three February twenty-nine are rejected. After the math, gestational age must land between zero and two hundred ninety-four days inclusive—zero through forty-two completed weeks. The required edd field accepts aliases due_date, estimated_due_date, and due; the required as_of field accepts reference_date, on, date, and today so spreadsheets and forms can map columns without renaming. Optional term_days defaults to two hundred eighty and must be an integer between two hundred fifty-nine and two hundred ninety-four inclusive (thirty-seven through forty-two weeks) when you model an early or late full-term assumption. If as_of falls before estimated LMP, gestational days go negative and the API returns invalid_input with a message that names the fields to check. If as_of is more than two hundred ninety-four days after estimated LMP, the request is likewise rejected so post-forty-two-week outliers never invent a continuing schedule. Missing fields, non-ISO shapes, and non-integer term_days produce the same invalid_input code; failed validation is never charged. Pricing for successful calls is a flat $0.002 per request with unit item.

Practical uses, limits, and how this differs from related tools

Prefer a dedicated days-between tool when you only need calendar distance without the obstetric term model; prefer this capability when the output must be gestational weeks, days, trimester, and days until EDD under an explicit term length. Pair examples deliberately: EDD two thousand twenty-six October fifteenth with as_of two thousand twenty-six May fifteenth for a mid-second-trimester result; the same EDD with as_of equal to the EDD for a clean forty weeks and zero days at term; and a missing or inverted pair to demonstrate invalid_input. This landing targets searches such as gestational age from due date calculator, how far along from EDD, and weeks pregnant from estimated delivery date. It is not a due-date-from-LMP calculator (that is a different search intent served by other KIT tools), not a pregnancy weight-gain table, not an ultrasound biometry engine, and not medical advice. The free browser tool runs entirely offline in your session; the API charges only successful solves at $0.002, keeps no durable copy of your dates after the response, and returns the same rounded integer fields every time so local goldens match production.