Sumyard

Due date calculator

Compare menstrual dating and a due date already established by your clinician.

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Calendar estimate only. Assumes a regular cycle with ovulation approximately 14 days before the next period. Menstrual dating is uncertain with irregular cycles.

Your inputs

Updates as you type

estimated due date

2027-05-08

Basis
Cycle-adjusted menstrual estimate

A calendar estimate; your maternity team's established date takes priority.

Calculations happen in your browser. Saving is optional.

How to use this tool

Choose menstrual dating or a clinician-established due date as the basis.

For menstrual dating, enter the period start and usual cycle length. For ultrasound or IVF dating, use the established clinical date rather than inferring one here.

Menstrual estimate = LMP + 280 days + (cycle−28); established dating is used unchanged

Worked example

2027-05-08 · estimated due date

Fixed example using the settings below. Monetary examples use USD; dates and times use their stated reference values. This example stays unchanged when you edit your calculation.

Example inputs
  • Dating basis: Last menstrual period
  • First day of last menstrual period: 2026-08-01
  • Usual cycle length (days): 28
  • Clinician-established due date: 2027-05-08

Method illustration: LMP 2026-08-01 with a 28-day cycle estimates 2027-05-08.

Assumptions and limits

  • Calendar estimate only. Assumes a regular cycle with ovulation approximately 14 days before the next period. Menstrual dating is uncertain with irregular cycles.
  • Ultrasound and clinical dating can change the estimated due date. Use the date established by your maternity team; a due date is not an exact birth date.
  • This tool does not independently date an ultrasound or IVF pregnancy. Enter the established clinical due date for those cases.

Method reference: NHS due date information

Check or report a result

Check the units, selected calculation and assumptions first. Compare the fixed example above with your inputs to identify what changed.

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