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Pregnancy Due Date Calculator

Estimate an LMP-based due date with usual-cycle adjustment and reproducible as-of gestational age, with clinical dating limits.

Use this result well

Inputs that matter
First LMP calendar date, whole usual cycle length from 20–45 days, and an explicit gestational-age as-of date
Output to expect
Cycle-adjusted LMP due-date estimate, preserved dates, estimated ovulation date, elapsed LMP-based weeks/days and distance from the estimate
How it works
Adds 280 days plus the entered cycle-length difference from 28 on a UTC-stable calendar-day axis; it never shifts the LMP through local midnight or silently assumes today
  • Treat this as a planning estimate only: uncertain LMP, irregular cycles, ART/IVF, ultrasound findings or clinical redating require a qualified prenatal clinician.
  • Do not use the result to diagnose pregnancy, assess symptoms, time tests or treatment, or delay urgent care; record the clinician-established obstetric EDD separately.

Choose your path

Built around the job you need to finish

Produce a calendar-stable, cycle-adjusted LMP planning estimate and reproducible as-of gestational age while keeping clinical dating, ART and diagnosis outside the calculator.

Adult with a known LMP and regular cycle

Record a planning estimate without a one-day timezone shift.

Enter the exact LMP, usual whole-day cycle length and explicit as-of date.

Sees preserved ISO dates, cycle adjustment and elapsed weeks/days.

Person with uncertain or irregular dates

Avoid false precision from a weak LMP assumption.

Review the method limitation and seek prenatal ultrasound/clinician dating.

Does not treat the browser result as the obstetric EDD.

Person after IVF or another ART procedure

Use embryo age and transfer records rather than an LMP shortcut.

Skip the LMP worksheet and use the fertility/prenatal team’s documented dating.

Preserves the clinician-established ART due date instead of recalculating it here.

Authoritative checks for this tool

Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.

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Reference & details

How it works

Conventional LMP estimate

ACOG describes the conventional estimated due date as 280 days after the first day of the LMP. This convention assumes a regular 28-day cycle and ovulation around day 14.

base EDD = first LMP day + 280 calendar days

Usual-cycle adjustment

The entered whole-day cycle difference from 28 is added to or subtracted from the base estimate. The estimated ovulation date is only the corresponding cycle assumption.

adjusted EDD = LMP + 280 + (cycle length − 28)

Calendar-stable as-of age

Strict YYYY-MM-DD fields are compared on a whole-calendar-day axis, preserving the entered LMP exactly. Clinical gestational age and EDD may be confirmed or revised using ultrasound or ART records.

Updated: August 2026

Example Scenarios

An adult enters 2026-01-01, a 30-day cycle and 2026-08-24 as the reference date, then records the two-day adjustment as a planning estimate.

A person sees that the input assumption is weak and uses prenatal care and ultrasound rather than presenting the browser estimate as an obstetric date.

A patient keeps the clinic's embryo-transfer-derived EDD and does not overwrite it with an LMP formula.

Common Mistakes to Avoid

Treating the estimated date as a guaranteed delivery date

Use it for planning only; a clinician establishes the best obstetric estimate and delivery timing varies.

Using the LMP worksheet for ART or to assess symptoms

Use embryo-transfer records and qualified care for ART; seek appropriate medical care for symptoms or concerns rather than relying on this calculator.

FAQ

It is an LMP-based planning estimate. The conventional 280-day method assumes a known LMP, a 28-day cycle and ovulation near day 14; irregular cycles, uncertain recall and variable ovulation reduce confidence. First-trimester ultrasound is the most accurate method to establish or confirm gestational age.

The worksheet adds the whole-day difference from 28 to the conventional 280-day estimate. This simple adjustment does not model irregular cycles or prove an ovulation date.

An explicit date makes the displayed LMP-based weeks and days reproducible. The calculator never silently assumes the device's current date.

Use the fertility or prenatal team's date based on embryo age and transfer records. ACOG recommends ART-derived gestational age rather than an LMP shortcut for these pregnancies.

No. Clinical redating depends on ultrasound timing, LMP reliability, ART records and professional assessment. Keep the documented obstetric EDD and discuss discrepancies with the prenatal team.

About Pregnancy Due Date Calculator

Enter the first day of the last menstrual period, usual whole-day cycle length, and an explicit as-of date. This is a planning estimate, not a clinical due date, pregnancy test, diagnosis, or substitute for prenatal care.