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Due Date Calculator

Estimate your baby’s due date from the first day of your last period, a known conception date or an IVF transfer date. You also get how many weeks pregnant you are on any date you pick, which trimester that is, and when the next ones begin.

Quick examples
days
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Estimated due dateSun, Jul 18, 2027
Gestational age
0 weeks 0 days
Trimester
First
Days until due date
280 days
Estimated conception
Sun, Oct 25, 2026
Second trimester starts (14 weeks)
Sun, Jan 17, 2027
Third trimester starts (28 weeks)
Sun, Apr 25, 2027
Early term begins (37 weeks)
Sun, Jun 27, 2027

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    Results you calculate here are kept on this device so you can come back to them.

      Formula

      Naegele’s rule: due date = first day of last period + 280 days (40 weeks)
      Cycle adjustment: add (cycle length − 28) days
      From conception: due date = conception date + 266 days
      From IVF transfer: due date = transfer date + 266 days − embryo age in days (day-5 transfer: + 261 days)
      Gestational age = days since the (adjusted) last period ÷ 7

      How to use it

      1. Choose what you know: last period, conception date or IVF transfer date.
      2. Enter the date. For a last period, set your usual cycle length if it is not 28 days; for IVF, choose the embryo age.
      3. Leave “as of” on today, or change it to see how far along you will be on another date.
      4. Read the due date, gestational age and trimester dates.

      Worked examples

      Last period began January 1, 2026 on a 28-day cycle; checked on April 1, 2026

      Estimated due date
      Thu, Oct 8, 2026
      Gestational age
      12 weeks 6 days
      Trimester
      First
      Days until due date
      190 days
      Estimated conception
      Thu, Jan 15, 2026
      Second trimester starts (14 weeks)
      Thu, Apr 9, 2026
      Third trimester starts (28 weeks)
      Thu, Jul 16, 2026
      Early term begins (37 weeks)
      Thu, Sep 17, 2026

      The same last period with a 32-day cycle (four days later)

      Estimated due date
      Mon, Oct 12, 2026

      A day-5 embryo transfer on March 10, 2026; checked on June 1, 2026

      Estimated due date
      Thu, Nov 26, 2026
      Gestational age
      14 weeks 4 days
      Trimester
      Second
      Second trimester starts (14 weeks)
      Thu, May 28, 2026

      Conception on February 14, 2026

      Estimated due date
      Sat, Nov 7, 2026

      How pregnancy is dated

      Pregnancy is counted from the first day of the last menstrual period, about two weeks before conception, which is why a full-term pregnancy is called 40 weeks even though the baby develops for about 38. Naegele’s rule assumes a 28-day cycle with ovulation on day 14; if your cycles are longer or shorter the calculator shifts the date by the difference.

      Trimesters here follow the usual convention: the first runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks. A pregnancy is early term from 37 weeks and full term from 39 weeks.

      How exact is a due date

      Only about 1 in 20 babies arrives on the estimated date; most are born within two weeks either side. An early ultrasound measurement is more reliable than period dates, and if the two disagree your care team may change your due date.

      This is an estimate for general information, not medical advice. Talk to a doctor or other qualified clinician before making health decisions based on it.

      Questions people ask

      How do I calculate my due date?

      Add 280 days to the first day of your last period — or count back three months and add a year and seven days. A last period that began on January 1 gives a due date of October 8.

      How is an IVF due date calculated?

      Add 266 days to the transfer date and subtract the embryo’s age. For a day-5 blastocyst transferred on March 10, the due date is 261 days later, November 26.

      What if my cycle is longer than 28 days?

      Ovulation is likely later, so the due date moves later by the same number of days. With a 32-day cycle, add four days to the standard date.

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