Skip to calculator
Veomark

Free · Instant · No signup

Pregnancy Due Date Calculator (Naegele's Rule)

Due date as LMP plus 280 days, plus gestational weeks from Date.now().

Page updated 2026-09-04.

Pregnancy Due Date Calculator (Naegele's Rule) visual
Sponsored
QuotVid free YouTube Shorts automation trial - get Shorts posted for you daily

Calculator

First day of LMP. Default 2026-01-15.

Calculated Results

Weeks pregnant

--

Days until due

--

Sponsored
QuotVid AI quote video studio - turn words into viral videos

Naegele's Rule, applied to one specific date

With a last menstrual period (LMP) of January 15, 2026, the estimated due date is October 22, 2026 -- as of today, that's roughly 34.8 weeks pregnant, with about 36 days remaining until the due date.

Naegele's Rule calculates the due date as LMP plus 280 days (40 weeks), based on the standard assumption of a 28-day cycle with ovulation around day 14 -- it's a widely used starting estimate precisely because LMP is a date most people can identify precisely, even though actual conception timing varies.

Weeks pregnant (34.8) is calculated from LMP to today's date, not to the due date -- pregnancy is conventionally counted from the start of the last period, not from the estimated conception date, which is why 'weeks pregnant' starts counting about 2 weeks before conception typically even occurs in a standard cycle.

Why this is a planning estimate, not a diagnosis

Naegele planning only. Ultrasound dating can differ. Not medical advice. Naegele's Rule assumes a standard 28-day cycle with ovulation on day 14 -- for anyone with a shorter, longer, or irregular cycle, actual conception and true due date can differ meaningfully from what this LMP-based formula estimates.

Early ultrasound dating (measuring fetal size, typically most accurate in the first trimester) is generally considered more precise than LMP-based dating alone, and many clinicians adjust the estimated due date based on ultrasound measurements rather than relying purely on Naegele's Rule.

Only a small percentage of babies are actually born exactly on their calculated due date -- the due date is a statistical midpoint estimate for a range of normal delivery timing (roughly a 5-week window is considered full-term), not a precise prediction of the actual birth day.

Related pregnancy planning tools

For estimating the fertile window and likely ovulation date in a planning or tracking context (before pregnancy, or for the next cycle), the Ovulation & Fertile Window Estimator uses related calendar-based logic.

Frequently Asked Questions (FAQ)

How is the October 22, 2026 due date calculated?

Naegele's Rule adds 280 days (40 weeks) to the last menstrual period date: January 15, 2026 + 280 days = October 22, 2026, based on the standard assumption of a 28-day cycle.

Why does 'weeks pregnant' start counting from the LMP rather than conception?

This is standard obstetric convention -- pregnancy is counted from the first day of the last menstrual period, not from the actual estimated conception date, which typically occurs about 2 weeks later in a standard cycle. This is why 'weeks pregnant' always runs about 2 weeks ahead of true fetal age.

How accurate is this if my cycle isn't exactly 28 days?

Naegele planning only. Ultrasound dating can differ. Not medical advice. Less accurate for irregular or non-28-day cycles, since Naegele's Rule assumes a standard 28-day cycle with ovulation on day 14. A different cycle length shifts actual conception timing away from this formula's assumption, which changes the true due date.

Is ultrasound dating more accurate than this LMP-based calculation?

Naegele planning only. Ultrasound dating can differ. Not medical advice. Generally considered more precise, especially when performed early in the first trimester, since it measures actual fetal size rather than relying purely on a calendar assumption from the last period. Clinicians often adjust the due date based on ultrasound findings.

Will the baby actually be born on the calculated due date?

Only a small percentage of babies are born exactly on their calculated due date -- it's a statistical estimate representing the middle of a normal delivery timing range (roughly a 5-week window is considered full-term), not a precise prediction of the actual birth day.

You might also need