Why is pregnancy counted from my last period?

Because the LMP is a date you can pin down, while the exact conception day usually isn't known. That's why "40 weeks" actually includes about 2 weeks before conception.

What are the trimesters?

First trimester is weeks 1–12, second is 13–26, and third is 27 until birth. This tool labels your current trimester from the weeks elapsed.

Pregnancy Due Date Calculator

Estimate your due date, current week, and trimester from your last period.

UPDATED · MAY 2026

First day of last period (LMP)

Naegele's rule: LMP + 280 days

Estimated due date

Oct 22, 2026

WEEKS ALONG—

TRIMESTER—

CONCEPTION ≈Jan 29, 2026

Due date

Oct 22, 2026

Weeks along

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Trimester

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How to use the Pregnancy Due Date Calculator

01
Enter your LMP. The first day of your last menstrual period.
02
Read your due date. Estimated using Naegele's rule (LMP + 280 days).
03
See your progress. Current week, trimester, and estimated conception date.

How is it calculated?

The standard estimate adds 280 days (40 weeks) to the first day of your last menstrual period — Naegele's rule. Gestational age is counted from that same LMP date, so "weeks along" is the time since your last period, and conception is estimated around 14 days after LMP (typical ovulation).

Frequently asked

The questions readers ask most about the pregnancy due date calculator.

Only about 4% of babies arrive exactly on the due date; most come within a week either side. An early ultrasound gives a more precise date than LMP alone.

How to use the Pregnancy Due Date Calculator

How is it calculated?

Frequently asked

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