Reverse Due Date Calculator

Enter the due date to estimate conception date or last menstrual period (LMP).

Please select a valid due date.
Typical range 20-45 days.
Default 14 days.
Results

Conception Date:

Last Menstrual Period (LMP):

Estimated Gestational Age at Due Date:

How it's calculated:

  • Due date is typically 280 days (40 weeks) from LMP.
  • Conception occurs approximately 14 days after LMP (adjusted for cycle length).
  • LMP = Due date - 280 days (adjusted for cycle length).
  • Conception = LMP + (cycleLength / 2) but limited to luteal phase.