Pregnancy Calculator

Find your due date, current week of pregnancy, and trimester from your last menstrual period.

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  • Works on all devices
Enter the first day of your last menstrual period to find your due date, current week, and trimester.
Defaults to today — change this to see the status on a different date.

Your result

14 weeks

Current week

Plus days5 days
Trimester2
Estimated due date08-03-2027
Days remaining177 days

AI explanation

Formula

Due date = last period date + 280 days (Naegele's rule). Current week = days since last period / 7

Worked example

LMP 2026-01-01, as of 2026-01-01

Worked example: LMP 2026-01-01, as of 2026-01-01
FieldValue
First day of last menstrual period01-01-2026
As of date01-01-2026
Estimated due date08-10-2026
Current week0
Trimester1

Assumptions

  • Uses Naegele's rule (280 days / 40 weeks from the last menstrual period), which assumes a regular 28-day cycle with ovulation on day 14 — actual due dates vary, especially with irregular cycles.
  • Trimesters are divided at week 13 (end of first trimester) and week 27 (end of second trimester), a common convention.
  • Informational only — always confirm dates and progress with your healthcare provider, especially if an ultrasound-based due date differs from this estimate.

Frequently asked questions

How is my due date calculated?

Using Naegele's rule: 280 days (40 weeks) after the first day of your last menstrual period, assuming a typical 28-day cycle.

Why might my ultrasound due date differ from this calculation?

Naegele's rule assumes a regular 28-day cycle with ovulation on day 14 — if your cycle is longer, shorter, or irregular, an early ultrasound (which measures fetal size directly) is generally more accurate.

When does each trimester start and end?

First trimester: weeks 1-13. Second trimester: weeks 14-27. Third trimester: weeks 28 until birth (around week 40).

Related calculators

Due Date CalculatorPregnancy Week CalculatorOvulation Calculator

Related articles

Health & Fitness1 min read

How a Pregnancy Due Date and Current Week Are Calculated

A pregnancy due date is simply the first day of the last menstrual period plus 280 days — and the current week and trimester follow from counting how many days have passed since that same starting date.

Read guide
Health & Fitness2 min read

Why the Pregnancy Due Date Formula Already Assumes a Specific Ovulation Day

Feeding the same last-period date into both the ovulation calculator and the pregnancy calculator shows exactly why Naegele's 280-day rule works for a typical 28-day cycle but drifts for a longer one — the due-date formula silently assumes ovulation on day 14, every time.

Read guide

Sources

This calculator provides a general estimate only and does not constitute personalized medical advice. Always confirm dates and monitor your pregnancy with a qualified healthcare provider.

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