RapidCheck

Pregnancy Due Date Calculator

Estimate your due date from your last menstrual period.

Last updated: 21 Aug 2026

Quick answer

The estimated due date is about 280 days (40 weeks) from the first day of your last menstrual period (LMP) — Naegele's rule. Enter your LMP above to get the due date and how many weeks along you are. This is an estimate; your doctor's dating scan is more precise.

Estimate your due date using the first day of your last menstrual period (LMP): due date ≈ LMP + 280 days (40 weeks). This is an estimate and not a substitute for medical advice or a dating scan.

How to calculate your due date

  1. 1 Enter the first day of your last menstrual period.
  2. 2 We add 280 days (40 weeks).
  3. 3 You see the estimated due date and how far along you are.

Frequently asked questions

How is the due date calculated?
By Naegele's rule: about 280 days (40 weeks) from the first day of your last period.
How accurate is it?
It is an estimate; only about 4% of babies arrive on the exact date. An early ultrasound gives more accurate dating.
Does it work with irregular cycles?
The LMP method assumes a ~28-day cycle; with irregular cycles, a scan-based due date is more reliable.

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