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Health & Fitness · Pregnancy

Pregnancy Due Date Calculator — Week by Week

Estimate your baby's due date from the first day of your last period (adjusted for your cycle length), the conception date, or an IVF embryo transfer (day 3, 5 or 6). See how many weeks pregnant you are today, your trimester, the estimated conception date, and the dates of key milestones through to full term.

How this is calculated

Due date = last period + 280 days + (cycle − 28) · = conception + 266 · = IVF transfer + 266 − embryo age (day 3 → 263, day 5 → 261)

Gestational age
Time since the first day of the last period (or the equivalent date for conception/IVF dating)
Term (ACOG)
Early term 37⁺⁰–38⁺⁶ weeks, full term 39⁺⁰–40⁺⁶, late term 41⁺⁰–41⁺⁶, post-term from 42⁺⁰

A pregnancy lasts about 280 days (40 weeks) from the first day of the last period — Naegele's rule. Longer or shorter cycles shift ovulation, so the date moves by the difference from 28 days. With a known conception or IVF transfer date the estimate is more precise: 266 days from fertilisation, so an embryo transferred at day 5 has 261 days to go.

Assumptions & sources

  • Singleton pregnancy; dates in your local calendar.
  • Ultrasound dating, when available, takes precedence.
  1. 1Methods for Estimating the Due Date (Committee Opinion No. 700) — American College of Obstetricians and Gynecologists
  2. 2Definition of Term Pregnancy (Committee Opinion No. 579) — American College of Obstetricians and Gynecologists
  3. 3How to calculate due date from embryo transfer date — San Diego Fertility Center

Calculator ID HLTH-PREG-DUE-001 · version 1.1.0

Common questions

How is the due date calculated?

Add 280 days (40 weeks) to the first day of your last period. If your cycle is longer than 28 days, add the extra days too.

How do I calculate my IVF due date?

Add 266 days minus the embryo's age to the transfer date: 263 days for a day-3 transfer, 261 for day 5, 260 for day 6.

How many weeks pregnant am I?

Count the weeks since the first day of your last period. This calculator shows it in weeks and days for today.