Pregnancy Week Calculator

Calculate the pregnancy week and due date from the last menstrual period (LMP).

Note: A medical-reference date calculation. The actual pregnancy week and due date can vary by ultrasound, individual condition, and a clinician's judgment.

Category: Date & Time

When to use?

Use it to find how many weeks and days pregnant you are based on the last menstrual period, and to see the due date.

How to use

  • Enter the last menstrual period (LMP) start date.
  • The current pregnancy week (weeks and days) is shown.
  • The due date (LMP + 280 days) is shown too.

Input Explanation

Enter the last menstrual period (LMP) start date accurately.

Calculation Basis

Pregnancy week = (today − LMP) ÷ 7. Due date = LMP + 280 days (40 weeks).

Usage Examples

  • Check pregnancy week - See the weeks and days as of a reference date, plus the due date.
  • Find the due date - Calculate the expected delivery date from the LMP.
  • Plan checkups - Check your current week to gauge prenatal checkup timing.

Examples

  • LMP 2023-01-01 → due date 2023-10-08
  • 70 days since LMP → 10 weeks 0 days

Cautions

  • This is a date-based reference. Confirm the exact pregnancy week and due date with an obstetric ultrasound.
  • Time-zone settings can cause a one-day difference in some cases.

Guides

Based on the last menstrual period

Pregnancy week is generally calculated from the last menstrual period start date, with the due date estimated about 280 days later.

Difference from medical judgment

The actual week and due date can differ from a clinician's judgment based on ultrasound, cycle, and individual condition.

FAQ

Is this for medical diagnosis?

No. It is a date-based reference; consult a clinician for accurate judgment.

How is the pregnancy week calculated?

It treats the LMP as 0 weeks 0 days and converts elapsed days into weeks and days.

How is the due date set?

It adds 280 days (40 weeks) to the LMP.

What if my cycle is irregular?

An irregular cycle increases the error of LMP-based calculation, so confirm with ultrasound results.

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