Due Date Calculator
Enter the first day of your last period (with your cycle length), the conception date, the embryo transfer date after IVF, or the date of an ultrasound and the gestational age it measured, to get your estimated due date, the dates of the early, full and late term periods (37 0/7 to before 42 0/7 weeks), the pregnancy week on a chosen day and the time left.
- Gestational age on the chosen day10 weeks, 0 days · week 11 · 1st trimester
- Time to the due date210 days (30 weeks, 0 days)
- Early, full and late term (37 0/7 – 41 6/7 weeks)09.05.2027 – 12.06.2027
- Postterm begins (42 0/7 weeks)13.06.2027
Birth timing classes and their dates
How it is calculated
The estimated due date (EDD) is the day gestational age reaches 40 weeks 0 days. Under the joint opinion of the American College of Obstetricians and Gynecologists (ACOG), the American Institute of Ultrasound in Medicine and the Society for Maternal–Fetal Medicine (Committee Opinion 700), it is by convention 280 days after the first day of the last period, a rule that assumes a regular 28-day cycle with ovulation on day 14. When a cycle differs from 28 days the difference lies mostly in the phase before ovulation, so the tool shifts the dates by the difference (a modified Naegele rule). That shift is a convention, not an ACOG recommendation. ACOG considers an ultrasound measurement in the first trimester (before 14 weeks 0 days) the most accurate way to date a pregnancy; when it differs markedly from the last period the doctor redates the pregnancy by the scan, while an ultrasound after 28 weeks is the least reliable method. For IVF, ACOG says the due date should be assigned from the embryo’s age and the transfer date: 261 days after transfer for a day-5 embryo, 263 days for a day-3 embryo. ACOG Committee Opinion 579 discourages using the single label “term” for all births from 37 0/7 to before 42 0/7 weeks and splits the period into three: early term 37 0/7 to before 39 0/7, full term 39 0/7 to before 41 0/7, late term 41 0/7 to before 42 0/7, postterm from 42 0/7 weeks; a birth before 37 completed weeks is preterm under the World Health Organization’s definition. The date is an average: in a study of 18,708 singleton pregnancies with spontaneous labour in Australia (Khambalia et al. 2013), only 5% of births fell on the due date and about 66% within 7 days either side. This page is for information only and is not medical advice; your doctor confirms your due date.
Start = LMP + (Cycle − 28) or Conception − 14 or Transfer − Embryo age − 14 or Scan date − Gestational age at the scan; EDD = Start + 280 days; Early–late term = Start + 37 × 7 … Start + 42 × 7 − 1LMP: first day of the last menstrual period. Start: the day gestational age is 0 weeks 0 days (the LMP of a 28-day cycle). EDD: estimated due date (40 weeks 0 days). Embryo age: days since fertilisation on the day the embryo was transferred (3 or 5). Early–late term: from 37 weeks 0 days to the day before 42 weeks 0 days (early, full and late term together).- From the last period: if your cycle is longer than 28 days, move the LMP forward by the difference; if shorter, back. With a 28-day cycle EDD = LMP + 280 days (Naegele’s rule).
- From conception: go back 14 days; conception is gestational day 14.
- After IVF: subtract the embryo’s age and 14 days from the transfer date. This matches ACOG’s rule: for a day-5 embryo EDD = transfer + 261 days, for a day-3 embryo transfer + 263 days.
- From an ultrasound: subtract the gestational age measured that day (weeks × 7 + days) from the scan date. The count starts from the day of the scan, not from today.
- Add 280 days to the start for the due date. Adding 37 × 7 days gives the first day of the early term period, 42 × 7 days the first postterm day.
- Divide the days from the start to the chosen day by 7: the quotient is completed weeks, the remainder days.
Example
The last period started on 17.08.2026 and the cycle is 28 days. The due date is 17.08.2026 + 280 days = 24.05.2027. Early to late term runs from 17.08.2026 + 259 days = 03.05.2027 to 17.08.2026 + 293 days = 06.06.2027; from 07.06.2027 the pregnancy is postterm. On 28.10.2026 it is 72 days = 10 weeks, 2 days, with 208 days to go. After IVF with a day-5 embryo transferred on 08.09.2026, the due date is 08.09.2026 + 261 days = 27.05.2027.
Frequently asked questions
Will my baby be born on the due date?
Usually not. In Khambalia and colleagues’ 2013 study only 5% of births fell on the due date and about 66% within a week either side. ACOG Committee Opinion 579 splits 37 0/7 to before 42 0/7 weeks into early, full and late term rather than one “term”; the tool gives the dates of those periods too.
How is the due date worked out after IVF?
Under ACOG Committee Opinion 700, from the embryo’s age and the transfer date: for a day-5 embryo (blastocyst) EDD = transfer + 261 days, for a day-3 embryo transfer + 263 days. This is the same as treating fertilisation as gestational day 14.
The ultrasound date differs from the one by my last period. Which counts?
Under ACOG, a first-trimester ultrasound measurement is more accurate than the date of the last period, and if they differ markedly the pregnancy is redated by the scan; your doctor makes that decision. If your doctor has redated the pregnancy, use the “Ultrasound measurement” option with that scan’s date and measured age. The calculation is anchored on the day of the scan, so the result does not change with today’s date.
Does the due date change if my cycle is not 28 days?
The tool shifts the dates by the difference from 28 days: 4 days forward for a 32-day cycle, 3 days back for a 25-day one. If your cycle is outside the 24–38 days FIGO counts as normal, or irregular, the estimate from the last period is weak and your doctor will date the pregnancy by ultrasound.
What if I am past my due date?
ACOG counts 41 0/7 to before 42 0/7 weeks as late term and 42 0/7 weeks and beyond as postterm. If you are past the due date, talk to your doctor about monitoring and timing; seek care without delay for fewer baby movements, leaking fluid or bleeding.
Source
- ACOG, AIUM, SMFM — Committee Opinion No. 700, Methods for Estimating the Due Date, Obstet Gynecol 2017;129(5):e150–e154, doi:10.1097/AOG.0000000000002046 (reaffirmed 2025): Background (EDD = LMP + 280 days; 28-day cycle, ovulation on day 14), “Clinical Considerations in the First Trimester” (first-trimester ultrasound most accurate; ART: “for a day-5 embryo, the EDD would be 261 days from the embryo replacement date … for a day-3 embryo … 263 days”), “Third Trimester” (least reliable) — archived copy of ACOG’s page
- ACOG, SMFM — Committee Opinion No. 579, Definition of Term Pregnancy, Obstet Gynecol 2013;122(5):1139–40, doi:10.1097/01.AOG.0000437385.88715.4a (reaffirmed 2025), Box 1 and text (the single label “term” for 37 0/7–41 6/7 is discouraged): early term 37 0/7–38 6/7, full term 39 0/7–40 6/7, late term 41 0/7–41 6/7, postterm 42 0/7 and beyond — archived copy of ACOG’s page
- ACOG Committee Opinion No. 700 — current ACOG page (abstract, “Reaffirmed 2025”)
- Khambalia AZ, Roberts CL, Nguyen M, Algert CS, Nicholl MC, Morris J, Predicting date of birth and examining the best time to date a pregnancy, Int J Gynaecol Obstet 2013;123(2):105–9, doi:10.1016/j.ijgo.2013.05.007, abstract “Results”: 5% of births on the estimated date, about 66% within 7 days (18,708 singleton pregnancies, spontaneous labour, Australia 2007–2011) — PubMed
- World Health Organization, Preterm birth fact sheet (10 May 2023), “Overview”: born alive before 37 completed weeks is preterm
- Darwish NA, Thabet SM, Aboul Nasr AL, El Sharkawy S, El Tamamy MN, Modified Naegele’s rule for determination of the expected date of delivery irrespective of the cycle length, Med J Cairo Univ 1994;62(1):39–47, p. 46 (Discussion): LMP + 7 days + 9 months, plus or minus the days by which the cycle exceeds or falls short of 28; the variation mostly affects the follicular phase (WHO EMRO IMEMR copy)
- Republic of Türkiye Ministry of Health, General Directorate of Public Health, Antenatal Care Management Guideline (Doğum Öncesi Bakım Yönetim Rehberi), publication no. 925, Ankara 2018: item 2.6 (p. 9: LMP, gestational age by ultrasound when unknown, due date) and item 6.2 (p. 16: danger signs in pregnancy) — copy in WHO’s policy database
- Munro MG et al. (FIGO), The FIGO ovulatory disorders classification system, Int J Gynaecol Obstet 2022;159(1):1–20, doi:10.1002/ijgo.14331, section 6.1.1: normal cycle 24–38 days at ages 18–45