Pregnancy Due Date

This pregnancy due date calculator estimates a delivery date from the first day of the last menstrual period (LMP) using the common obstetric rule: add 280 days (40 weeks) to LMP. It is a calendar planning aid only — not medical advice, not a substitute for prenatal care, and not adjusted for ultrasound dating or individual health factors. Always confirm timing with a qualified clinician.

What LMP-based dating means

Healthcare providers often date pregnancies from LMP because the first day of the last period is usually easier to recall than conception date. The 280-day (40-week) convention assumes a 28-day cycle with ovulation around day 14. Real cycles vary; ovulation timing shifts the true gestational age even when LMP math is standard on paper.

Enter the LMP date shown on intake forms or pregnancy apps that use the same rule. The tool returns one estimated due date plus a plain-language note that clinical confirmation is required.

When this estimate is useful

Expectant parents rough-plan parental leave, notify employers, and coordinate family travel around a target month. Partners mark milestones on a shared calendar before the first prenatal visit. Teachers and coaches planning around a due season can see which month window is likely — understanding that only about five percent of babies arrive on the exact estimated date.

Use days until for a live countdown once you have a due date from your care team. Measure spans between prenatal appointments with days between dates.

Limits of LMP math

Ultrasound dating in the first trimester often revises the due date when it differs from LMP by more than a few days. Irregular cycles, recent hormonal contraception, and assisted reproduction break the default 280-day assumption. This calculator does not accept conception date, IVF transfer day, or crown-rump length — those require clinician-specific formulas.

Do not use this page for medical decisions about induction, medication timing, or emergency symptoms. It performs civil-date addition only in your browser; nothing is stored on a server.

280 days vs 40 weeks

Forty weeks times seven days equals 280 days on the calendar. Some sources describe pregnancy as ten lunar months; others cite 266 days from conception. This tool follows the LMP + 280-day convention used on many patient handouts in the US. If your clinic quotes a different due date, trust their chart — they may have adjusted for ultrasound or cycle length.

Leap day is handled automatically when the 280-day span crosses February 29. For week-based planning (“32 weeks today”), divide elapsed days by seven on the weeks between dates tool using LMP as the start date.

Planning around a due month

Treat the due date as the center of a four-week window, not a single guaranteed day. Mark the month on monthly calendars and note federal holidays on 2026 holidays if travel or hospital logistics matter. Employer paperwork may ask for “expected week of delivery” — round to the week containing the estimated date rather than quoting a false precision.

Half-birthday and age milestones for siblings can be checked on the age calculator separately from pregnancy timing.

Worked example

LMP was January 10. Enter that date; the tool adds 280 calendar days to reach an estimated due date in mid-October. If the first ultrasound shifts dating by one week, replace the displayed date with the clinic’s figure for leave forms while keeping this page as a record of the original LMP-based estimate.

Leave paperwork and HR forms

Employer leave forms may ask for “expected delivery date” or “due date per provider.” Use the clinic’s figure when you have one; use this LMP estimate only when filling a draft before the first visit. Short-term disability policies sometimes measure eligibility from a different anchor — read the policy booklet rather than assuming LMP + 280 matches insurance language.

Partners coordinating shared leave can mark both the estimated date and a two-week window on monthly calendars, then update after anatomy scan dating without treating this page as a medical record.

Childcare waitlists often ask for “due month” rather than a single day. Round to the calendar month containing the estimate and renew the month if ultrasound shifts dating — avoid quoting false precision in forms that only need seasonal planning.

Gestational age vs LMP dating

Clinic conversations often cite “12 weeks” gestational age while this page outputs a due date from LMP. Gestational weeks typically count from LMP as well in US obstetric convention, but ultrasound re-dating can shift both the displayed due date and the week number. Track the clinician’s chart as authoritative when week-based milestones (screening windows) matter more than a single calendar due day.

Related tools

General date arithmetic lives on the date calculator and date tools hub. Recurring prenatal visit schedules can be drafted on recurring dates. This site does not provide medical guidance — contact your healthcare provider for all clinical questions.