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UK pregnancy reference

UK Pregnancy Due Date Calculator

Estimate a pregnancy due date from the first day of the last period. NHS or maternity care may confirm a different date.

Estimated due date

CalculatingNHS-style 40-week estimate from LMP.

Inputs

Formula basis
  • Estimated due date = first day of last period + 280 days, adjusted by cycle length.
  • Pregnancy dating may be changed by a scan or clinical review.

Calculation Basis and Official Sources

Uses the common 280-day or 40-week estimate from the first day of the last period.

Official rules change often. Before filing, borrowing, signing, paying or relying on a result, check GOV.UK, HMRC, your lender, contract party or a qualified adviser.

Medical and Legal Disclaimer

This calculator gives a rough pregnancy dating estimate only. It is not medical advice, diagnosis, treatment, antenatal care guidance, emergency guidance, legal advice, insurance advice or any other professional advice.

Actual dating can change after ultrasound, ovulation timing, cycle irregularity, IVF dating, multiple pregnancy, miscarriage history, medical risk factors or clinician review. Use the date given by your midwife, GP, NHS service or maternity team as the official reference.

Calcitda does not guarantee accuracy, completeness, timeliness or suitability. To the fullest extent permitted by law, Calcitda and its operator are not responsible for losses, injuries, claims or decisions arising from use of, or reliance on, this calculator. Nothing here limits liability that cannot legally be limited.