Due Date Calculator
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Results
Estimated due date: Thursday, July 8, 2027. Full term runs Jul 1–14, 2027.
| Category | Gestational age | Your dates |
|---|---|---|
| Preterm | Before 37 weeks 0 days | Before Jun 17, 2027 |
| Early term | 37 weeks 0 days to 38 weeks 6 days | Jun 17–30, 2027 |
| Full term | 39 weeks 0 days to 40 weeks 6 days | Jul 1–14, 2027 |
| Late term | 41 weeks 0 days to 41 weeks 6 days | Jul 15–21, 2027 |
| Post-term | 42 weeks 0 days and beyond | From Jul 22, 2027 |
Only about 1 in 20 women give birth on their due date (ACOG), so treat it as the middle of a window rather than a deadline. Your care provider may adjust the date after an ultrasound.
Pregnancy dates are estimates, not medical advice. Follow the dates and care plan from your doctor or midwife, and talk to them about anything that worries you.
How to use the due date calculator
- Choose what you know: your last period, the date you conceived, or the date of an IVF embryo transfer.
- Enter the date. For your last period, also enter your usual cycle length (28 days if you are not sure). For IVF, choose a day-3 or day-5 embryo.
- Read the estimated due date and your term windows. If you want to know how far along you are today, use the pregnancy calculator.
Due date formula (Naegele's rule)
cycle adjustment = + (cycle length − 28) days
from conception: due date = conception + 266 days
from IVF: due date = transfer + 261 days (day-5 embryo) or + 263 days (day 3)
calendar shortcut: last period + 1 year − 3 months + 7 days
Naegele's rule, named after the 19th-century obstetrician Franz Naegele, puts the due date 40 weeks (280 days) after the first day of the last period. ACOG uses the same 280-day convention. It assumes ovulation about 14 days into a 28-day cycle, so a longer cycle moves the date later and a shorter one earlier. Conception happens about two weeks after the period starts, which is why a known conception date adds 266 days (38 weeks). For IVF, ACOG counts from the transfer and the embryo's age. The old calendar shortcut is quick to do in your head, but months have different lengths, so it can land a few days away from the 280-day count.
Worked example
Your last period started on Oct 1, 2026 and your cycles are 28 days. Adding 280 days gives Thursday, July 8, 2027. With a 32-day cycle the date moves 4 days later, to Jul 12, 2027. A conception date of October 15, 2026 gives Jul 8, 2027, and a day-5 embryo transferred on October 20, 2026 gives Jul 8, 2027. For the first example, full term runs Jul 1–14, 2027.
Term definitions and your dates
ACOG and the Society for Maternal-Fetal Medicine define these categories. The dates are for the worked example.
| Category | Gestational age | Dates for a period on Oct 1, 2026 |
|---|---|---|
| Early term | 37 weeks 0 days to 38 weeks 6 days | Jun 17–30, 2027 |
| Full term | 39 weeks 0 days to 40 weeks 6 days | Jul 1–14, 2027 |
| Late term | 41 weeks 0 days to 41 weeks 6 days | Jul 15–21, 2027 |
| Post-term | 42 weeks 0 days and beyond | From Jul 22, 2027 |
Birth before 37 weeks 0 days is preterm. Only about 1 in 20 women give birth on their due date, according to ACOG, so think of it as the middle of a window rather than a deadline.
Due dates by month
Due dates for a last period on the first of each month in 2026 (28-day cycle), by the 280-day count and by the calendar shortcut.
| Last period | Due date (280 days) | Calendar shortcut | Difference |
|---|---|---|---|
| Jan 1, 2026 | Oct 8, 2026 | Oct 8, 2026 | Same |
| Feb 1, 2026 | Nov 8, 2026 | Nov 8, 2026 | Same |
| Mar 1, 2026 | Dec 6, 2026 | Dec 8, 2026 | +2 days |
| Apr 1, 2026 | Jan 6, 2027 | Jan 8, 2027 | +2 days |
| May 1, 2026 | Feb 5, 2027 | Feb 8, 2027 | +3 days |
| Jun 1, 2026 | Mar 8, 2027 | Mar 8, 2027 | Same |
| Jul 1, 2026 | Apr 7, 2027 | Apr 8, 2027 | +1 days |
| Aug 1, 2026 | May 8, 2027 | May 8, 2027 | Same |
| Sep 1, 2026 | Jun 8, 2027 | Jun 8, 2027 | Same |
| Oct 1, 2026 | Jul 8, 2027 | Jul 8, 2027 | Same |
| Nov 1, 2026 | Aug 8, 2027 | Aug 8, 2027 | Same |
| Dec 1, 2026 | Sep 7, 2027 | Sep 8, 2027 | +1 days |
How cycle length changes the date
| Cycle length | Due date for a period on Oct 1, 2026 |
|---|---|
| 24 days | Jul 4, 2027 |
| 26 days | Jul 6, 2027 |
| 28 days | Jul 8, 2027 |
| 30 days | Jul 10, 2027 |
| 32 days | Jul 12, 2027 |
| 35 days | Jul 15, 2027 |
Things to know about due dates
- An early scan can change it. ACOG calls a first-trimester ultrasound the most accurate way to set the due date, and your provider may revise the date after one.
- Irregular cycles reduce accuracy. The cycle adjustment assumes the same length every month and a 14-day gap between ovulation and the next period.
- Twins and other multiples often arrive earlier than the due date; your care team will plan with you.
All dates here are estimates. This is not medical advice; talk to your doctor or midwife. To estimate when you conceived, use the pregnancy conception calculator.
Sources
- ACOG, AIUM and SMFM, Committee Opinion 700: Methods for Estimating the Due Date (2017).
- ACOG and SMFM, Committee Opinion 579: Definition of Term Pregnancy (2013).
- ACOG FAQ, How Your Fetus Grows During Pregnancy (January 2024).
Frequently asked questions
How is a due date calculated?
By Naegele’s rule: add 280 days (40 weeks) to the first day of your last period. A period that started on October 1, 2026 gives a due date of July 8, 2027. With a cycle longer or shorter than 28 days, move the date by the difference.
How does cycle length change my due date?
The rule assumes ovulation on about day 14 of a 28-day cycle. A longer cycle usually means later ovulation, so each extra day moves the due date a day later: for a period on October 1, 2026, a 32-day cycle gives July 12, 2027 instead of July 8.
Can I work out my due date from the conception date?
Yes. Add 266 days (38 weeks) to the conception date. Conception on October 15, 2026 gives a due date of July 8, 2027. For IVF, ACOG adds 261 days to a day-5 embryo transfer date or 263 days to a day-3 transfer.
What do early term, full term and late term mean?
ACOG and SMFM define early term as 37 weeks 0 days to 38 weeks 6 days, full term as 39 weeks 0 days to 40 weeks 6 days, late term as 41 weeks 0 days to 41 weeks 6 days, and post-term as 42 weeks or more. Birth before 37 weeks is preterm.
How likely is it that my baby arrives on the due date?
Not very: ACOG says only about 1 in 20 women give birth on their due date. The due date marks 40 weeks, the middle of the full-term window, which runs for two weeks from 39 weeks 0 days.