When is my due date?
Enter the first day of your last period, your conception date, or the result of an ultrasound. See your estimated due date and how many weeks pregnant you are.
- Estimated due date
- Tuesday, May 11, 2027
Your estimated due date is Tuesday, May 11, 2027.
- How far along
- 8 weeks
- Trimester
- First trimester
- Days until the due date
- 224
- Likely conception date
- August 18, 2026
- Full term from
- May 4, 2027
- Full term to
- May 17, 2027
- Pregnancy counted from
- August 4, 2026
Answer for the example date Tuesday, September 29, 2026. It changes to today's date when the page loads.
Estimated due date: Tuesday, May 11, 2027. Your estimated due date is Tuesday, May 11, 2027.
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Estimates a pregnancy due date: 280 days after the first day of the last period (adjusted for cycle length), 266 days after conception, or from an ultrasound, with how far along the pregnancy is.
Example with the default inputs (Based on Last period, First day of your last period August 4, 2026, Cycle length (days) 28, Work out on September 29, 2026) on the example date Tuesday, September 29, 2026: Your estimated due date is Tuesday, May 11, 2027.
Method: Due date = start + 280 days, where the start is the first day of the last period + (cycle length − 28) days, the conception date − 14 days, or the ultrasound date − the gestational age it gave.
- A pregnancy is counted from the first day of the last period and lasts 280 days (40 weeks) to the due date (ACOG).
- Ovulation and conception happen 14 days before the next period would start, so a cycle longer or shorter than 28 days moves the dates by the difference.
- Trimesters: first to 13 weeks 6 days, second to 27 weeks 6 days, third after. Full term is 39 weeks 0 days to 40 weeks 6 days.
- How far along is left out before the start or more than 44 weeks after it, and a note says to check the dates.
- An estimate, not medical advice: a first-trimester ultrasound is the most accurate way to date a pregnancy.
Worked examples
Each example is checked against the calculator on every build.
- Based on Last period, First day of your last period 2026-01-01, Cycle length (days) 28, Work out on 2026-03-15 gives Estimated due date 2026-10-08, How far along 10 weeks, 3 days, Trimester First trimester, Days until the due date 207, Date of conception 2026-01-15, Full term from 2026-10-01, Full term to 2026-10-14.Source: ACOG Committee Opinion 700 (LMP + 280 days); ACOG CO 579 (full term); hand calculation in content.mdx
- Based on Last period, First day of your last period 2027-12-01, Cycle length (days) 35, Work out on 2027-12-01 gives Pregnancy counted from 2027-12-08, Estimated due date 2028-09-13, Date of conception 2027-12-22.Source: ACOG CO 700 with the cycle-length adjustment in content.mdx; hand calculation in content.mdx
- Based on Conception date, Date of conception 2026-06-10, Work out on 2026-09-27 gives Pregnancy counted from 2026-05-27, Estimated due date 2027-03-03, How far along 17 weeks, 4 days, Trimester Second trimester.Source: ACOG CO 700 (280 days from the LMP, conception on day 14, so 266 days from conception); hand calculation in content.mdx
- Based on Ultrasound, Ultrasound date 2026-08-20, Weeks at the scan 12, And days 3, Work out on 2026-08-20 gives Pregnancy counted from 2026-05-25, Estimated due date 2027-03-01, How far along 12 weeks, 3 days, Days until the due date 193.Source: ACOG CO 700 (dating by ultrasound); hand calculation in content.mdx
How it works
The calculator first finds the start of the pregnancy count (day 0, week 0), then adds 280 days.
- Last period: start = first day of the last period + (cycle length − 28) days
- Conception date: start = conception date − 14 days
- Ultrasound: start = ultrasound date − (weeks × 7 + days) the scan gave
Due date = start + 280 days (40 weeks). With a 28-day cycle, this is Naegele's rule: the first day of the last period plus 280 days. From a conception date, it is conception + 266 days.
The cycle adjustment comes from two facts: a pregnancy dated from the last period assumes ovulation (and conception) on day 14 of a 28-day cycle (ACOG), and ovulation happens about 14 days before the next period would start. So in a cycle of C days, ovulation is on day C − 14, which is C − 28 days later than in a 28-day cycle. Cycle length can be 21 to 45 days.
The calculator also shows, on the work-out date (today unless you change it under "Use another date"):
- How far along: days = work-out date − start, shown as whole weeks and days (days ÷ 7, and the remainder). It is left out if the date is before the start or more than 308 days (44 weeks) after it. Then a note says to check the dates: "Before the pregnancy count starts" for a last period after the work-out date, and "More than 44 weeks after the pregnancy count starts" when the due date is long past.
- Trimester: "First trimester" under 98 days (to 13 weeks 6 days), "Second trimester" under 196 days (to 27 weeks 6 days), "Third trimester" under 294 days, then "Past 42 weeks (post-term)".
- Days until the due date: 280 − days, shown up to the due date.
- Likely conception date: start + 14 days.
- Full term (ACOG): start + 273 days (39 weeks 0 days) to start + 286 days (40 weeks 6 days).
All dates are calendar dates with no time of day, so time zones and daylight saving do not change them.
Assumptions
- Cycles are regular. Real cycles and ovulation days vary (Bull and others, 2019), which is why a first-trimester ultrasound dates a pregnancy best.
- IVF due dates use the embryo's age and transfer date instead.
- This calculator gives an estimate. It is not medical advice. Your obstetric provider sets your due date; talk to them about your pregnancy.
Worked examples by hand
Last period January 1, 2026, 28-day cycle, worked out on March 15, 2026. Start = January 1 + 0 days. Due date = January 1 + 280 days. January has 31 days, so counting on: February 1 is day 31, March 1 day 59, and so on to October 8, 2026 (day 280). On March 15 (day 73): 73 = 10 × 7 + 3, so 10 weeks 3 days, first trimester, 280 − 73 = 207 days to go. Likely conception: January 15. Full term: October 1 to October 14, 2026.
Last period December 1, 2027, 35-day cycle. Start = December 1 + (35 − 28) = December 8, 2027. Due date = December 8, 2027 + 280 days = September 13, 2028 (2028 is a leap year, so February has 29 days). Likely conception: December 22, 2027.
Conception June 10, 2026, worked out on September 27, 2026. Start = June 10 − 14 = May 27, 2026. Due date = May 27 + 280 days = March 3, 2027 (266 days after June 10). On September 27: 123 days = 17 weeks 4 days, second trimester.
Ultrasound on August 20, 2026 at 12 weeks 3 days. 12 × 7 + 3 = 87 days, so start = August 20 − 87 days = May 25, 2026. Due date = May 25, 2026 + 280 days = March 1, 2027. On the scan date, 280 − 87 = 193 days are left.
Other questions people ask
How is a due date calculated?
A due date is 280 days (40 weeks) after the first day of your last menstrual period. This is Naegele's rule, and it is how the American College of Obstetricians and Gynecologists (ACOG) describes dating from the last period. For example, a last period that started on January 1, 2026 gives a due date of October 8, 2026.
What if my cycle is not 28 days?
The 280-day rule assumes a 28-day cycle with ovulation on day 14. Ovulation usually happens about 14 days before the next period, so in a longer cycle it happens later. The calculator moves the dates by your cycle length minus 28 days: a 35-day cycle moves the due date 7 days later.
How do I calculate my due date from the conception date?
Add 266 days (38 weeks) to the conception date. This is the same as counting 280 days from a last period 14 days before conception.
Why does my ultrasound give a different due date?
ACOG says an ultrasound in the first trimester (up to 13 weeks 6 days) is the most accurate way to date a pregnancy. If your provider changed your due date after a scan, choose "Ultrasound" and enter the scan date and the weeks and days it gave.
How accurate is a due date?
It is an estimate. Only a small share of babies arrive on the exact day, and most are born in the weeks around it. ACOG calls 39 weeks 0 days to 40 weeks 6 days full term, and the calculator shows those dates too.
What are the trimesters?
The first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days until birth. Weeks are counted from the first day of the last period, so you are about 2 weeks pregnant at conception.