Health
Due Date Calculator
Estimated due date from your last period or conception date, how many weeks pregnant you are, trimester and timeline.
Updated: ACOG CO 700
Result
Updates as you typeEstimated due date (Monday)
17 May 2027
- Today
- 11 weeks 2 days (day 79)
- Trimester
- first
- Days to go
- 201 days (28 weeks)
- Pregnancy start (week 0)
- 10 August 2026
- Estimated conception
- 24 August 2026
- Second trimester starts (14+0)
- 16 November 2026
- Third trimester starts (28+0)
- 22 February 2027
- Term window (37+0 to 41+6)
- 26 April 2027 – 31 May 2027
How it's calculated
Pregnancy is dated from the first day of the last menstrual period and lasts 280 days (40 weeks) on average. The due date is that day plus 280 days (Naegele's rule), shifted by the difference when the cycle is not 28 days. From a conception or embryo-transfer date, 266 days are added. Today's week is the number of days since the adjusted start divided by 7. A first-trimester ultrasound that disagrees takes precedence.
Worked example
Last period started 10 August 2026, 28-day cycle, today 28 October 2026:
- Due date: 10 August 2026 + 280 days = 17 May 2027
- Today: day 79 = 11 weeks 2 days, first trimester; 201 days to go
- Second trimester 16 November 2026, third 22 February 2027, term from 26 April 2027
Week-by-week timeline
| Week | Date | Note |
|---|---|---|
| Week: 4+0 | Date7 September 2026 | NoteMissed period; a test may be positive |
| Week: 8+0 | Date5 October 2026 | Note |
| Week: 12+0 | Date2 November 2026 | NoteFirst-trimester screening (11–14 weeks) |
| Week: 14+0 | Date16 November 2026 | NoteSecond trimester starts |
| Week: 20+0 | Date28 December 2026 | NoteAnomaly scan (18–22 weeks) |
| Week: 24+0 | Date25 January 2027 | NoteGlucose test (24–28 weeks) |
| Week: 28+0 | Date22 February 2027 | NoteThird trimester starts |
| Week: 32+0 | Date22 March 2027 | Note |
| Week: 36+0 | Date19 April 2027 | Note |
| Week: 37+0 | Date26 April 2027 | NoteTerm begins |
| Week: 40+0 | Date17 May 2027 | NoteEstimated due date |
| Week: 42+0 | Date31 May 2027 | NotePost-term |
Frequently asked questions
How is the due date calculated?
By Naegele's rule: 280 days (40 weeks) are added to the first day of your last period. For a last period starting 10 August 2026 the due date is 17 May 2027. If your cycle is longer or shorter than 28 days, the difference is added or subtracted. From a known conception date, 266 days are added.
How many weeks pregnant am I?
Pregnancy is counted from the first day of the last period, so the two weeks before conception are included. Divide the days between that date and today by 7: 104 days is 14 weeks and 6 days.
Which weeks are the trimesters?
The first trimester runs to 13 weeks 6 days, the second from 14 weeks to 27 weeks 6 days, and the third from 28 weeks to birth. From 37 weeks the baby is at term; after 42 weeks the pregnancy is post-term.
My ultrasound gave a different date. Which one counts?
A first-trimester ultrasound is the most accurate method. ACOG advises that when the ultrasound date differs from the period-based date by more than a set margin (5 to 7 days in early pregnancy), the due date is changed to the ultrasound date and then kept.
Will the baby arrive on the due date?
Rarely. The due date marks the end of week 40; most births happen between 37 and 42 weeks. The date is a reference for timing checks and tests.
What if I don't know the date of my last period?
Use the conception date if you know it. Otherwise your doctor will date the pregnancy from the first ultrasound; enter that due date here to see your week and timeline.
Sources
A calendar calculation, not a medical assessment. Ultrasound dating, irregular cycles and fertility treatment can change the date; follow your care provider's schedule. Results are for guidance only.