Pregnancy Due Date Calculator

Calculate your estimated due date from your last menstrual period. See key milestones and trimester progress.

Last updated: April 2026 · Source: NHS — Due date calculator

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

The estimated due date (EDD) is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is known as Nägele's rule: add 7 days to the LMP date, then add 9 calendar months (or subtract 3 months and add 1 year). The method assumes a 28-day cycle with ovulation on day 14.

If you know the conception date, the calculator adds 266 days (38 weeks) instead. For cycles longer or shorter than 28 days, the due date is adjusted accordingly — for example, a 35-day cycle shifts the EDD forward by 7 days.

The NHS offers all pregnant women a dating scan between 8 and 14 weeks, which measures the baby's crown-rump length to refine the due date. Only about 4% of babies arrive on their exact due date; most are born within two weeks either side. The NHS considers pregnancies overdue at 42 weeks.

Example: LMP 1 January 2026, 28-day cycle

  1. LMP: 1 January 2026
  2. Add 7 days: 8 January 2026
  3. Add 9 months: 8 October 2026
  4. Estimated due date: 8 October 2026
  5. First trimester ends: ~27 March 2026 (week 12)

Source: NHS — Due date calculator

Frequently Asked Questions

What does the Pregnancy Due Date Calculator do?
Calculate your estimated due date from your last menstrual period. See key milestones and trimester progress. All calculations are performed in your browser using official UK rates and thresholds.
Is this medical advice?
No. This calculator is for informational purposes only and does not constitute medical advice. Always consult your GP or an appropriate healthcare professional for medical guidance.
Are the reference values from the NHS?
Where applicable, this calculator uses reference values and guidelines from the NHS and other UK health authorities. Individual needs may vary based on personal health circumstances.