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Pregnancy Due Date Calculator

Estimate a due date from the last period, conception or embryo transfer, with gestational age at a reference date.

Your numbers

Make it your own
Updates as you type
Estimated due date
2026-10-08

Calculated from your inputs · rounded for display

Gestational age at reference date10 weeks 0 days
Days until estimated due date210

An educational estimate, not a diagnosis or a delivery prediction. A clinician’s established due date, ultrasound dating and IVF records take priority. Cycle adjustment assumes a regular cycle.

Your calculation, step by step

No black boxes
  1. Last menstrual period + 280 days + (28 − 28) cycle adjustment.
  2. Gestational age is measured from estimated due date minus 280 days.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

LMP + 280 + (cycle−28) days; conception + 266; IVF transfer + 266 − embryo age

Calendar dating is an estimate. LMP adjustment assumes a regular cycle; known conception and embryo transfer have separate offsets. Clinical dating and ultrasound assessment take priority. A due date does not predict the exact day of delivery. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.

A worked example

With an LMP of January 1, 2026 and a 28-day cycle, estimated due date is October 8, 2026. At March 12, estimated gestational age is 10 weeks, 0 days.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

What assumptions does this calculation use?

Calendar dating is an estimate. LMP adjustment assumes a regular cycle; known conception and embryo transfer have separate offsets. Clinical dating and ultrasound assessment take priority. A due date does not predict the exact day of delivery.

Can I save or check a scenario?

The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.

Sources & methodology

NHS: due date estimation ↗

Formula review: October 24, 2026. Read our methodology.