Due Date Calculator: Pregnancy, IVF and Gestational Age

Due Date Calculator

Estimate a pregnancy due date and gestational age from the last menstrual period, conception or ovulation, an IVF embryo transfer, or a known due date.

Estimate only: pregnancy dating can change after clinical assessment or ultrasound. Contact a qualified clinician for medical decisions, unusual symptoms, or uncertainty about dates.


How the estimated due date is calculated

Pregnancy dating normally counts 40 weeks, or 280 days, from the first day of the last menstrual period. A conception or ovulation date starts about two weeks later, so the equivalent estimate is 266 days from conception.

  • LMP: first day of the last period + 280 days, adjusted by the entered cycle length minus 28 days.
  • Conception or ovulation: entered date + 266 days.
  • IVF transfer: transfer date + 263 days for a day-3 embryo or +261 days for a day-5 embryo.
  • Known due date: counts backward 280 days for an estimated gestational start and 266 days for estimated conception.

Examples

  • An LMP of January 1, 2026 with a 28-day cycle gives an estimated due date of October 8, 2026.
  • The same LMP with a 30-day cycle gives October 10, 2026.
  • A conception date of January 15, 2026 gives October 8, 2026.
  • A day-5 embryo transfer on January 20, 2026 gives October 8, 2026.
  • A day-3 embryo transfer on January 18, 2026 also gives October 8, 2026.
  • A known due date of October 8, 2026 corresponds arithmetically to an estimated LMP of January 1, 2026.

Important medical limits

  • A due date is an estimate, not a prediction of the delivery day.
  • Irregular cycles, uncertain bleeding dates, assisted reproduction details, and ultrasound findings can change clinical dating.
  • The cycle-length adjustment is a simple calendar assumption and does not confirm ovulation.
  • Do not use this calculator to diagnose pregnancy, assess fetal health, or decide when to seek care.
  • Urgent symptoms require prompt professional medical assessment regardless of the calculated week.

Sources and related calculators

Dating conventions and term definitions follow the general framework described by the American College of Obstetricians and Gynecologists and its definition of term pregnancy. These references do not make the calculator a clinical assessment.

Use the Ovulation Calculator for cycle-based fertile-window estimates or the Date Calculator for general calendar arithmetic.