Due Date Calculator
Your due date is the first day of your last period plus 280 days. Enter that date and your cycle length to see it with trimester dates and weeks pregnant. How it works
Use the Due Date Calculator
About the Due Date Calculator
Your due date is the first day of your last period plus 280 days, which is 40 weeks. If your last period began on January 1, 2026, the due date is October 8, 2026. For a cycle that is not 28 days long the calculator moves the date by the difference, so a 35-day cycle adds 7 days.
Key pregnancy dates counted from the last period
| Date | Days after the last period began | Weeks and days | If the last period began January 1, 2026 |
|---|---|---|---|
| Estimated conception | 14 days | 2 weeks 0 days | January 15, 2026 |
| Second trimester starts | 98 days | 14 weeks 0 days | April 9, 2026 |
| Third trimester starts | 196 days | 28 weeks 0 days | July 16, 2026 |
| Early term begins (37 weeks) | 259 days | 37 weeks 0 days | September 17, 2026 |
| Full term begins (39 weeks) | 273 days | 39 weeks 0 days | October 1, 2026 |
| Due date | 280 days | 40 weeks 0 days | October 8, 2026 |
| End of 42 weeks | 294 days | 42 weeks 0 days | October 22, 2026 |
For a 28-day cycle. ACOG calls 37 weeks 0 days through 38 weeks 6 days early term and 39 weeks 0 days through 40 weeks 6 days full term, and the calculator labels the two start dates the same way.
Due date by cycle length
| Average cycle | Due date is the last period plus | Due date if the last period began January 1, 2026 | Estimated conception |
|---|---|---|---|
| 21 days | 273 days | October 1, 2026 | January 8, 2026 |
| 24 days | 276 days | October 4, 2026 | January 11, 2026 |
| 26 days | 278 days | October 6, 2026 | January 13, 2026 |
| 28 days | 280 days | October 8, 2026 | January 15, 2026 |
| 30 days | 282 days | October 10, 2026 | January 17, 2026 |
| 32 days | 284 days | October 12, 2026 | January 19, 2026 |
| 35 days | 287 days | October 15, 2026 | January 22, 2026 |
| 40 days | 292 days | October 20, 2026 | January 27, 2026 |
| 45 days | 297 days | October 25, 2026 | February 1, 2026 |
The calculator accepts whole cycle lengths from 21 to 45 days and shifts every date it shows by cycle length − 28 days.
Methodology
Due date = first day of the last menstrual period (LMP) + 280 days. This is the convention ACOG describes, and it assumes a 28-day cycle with ovulation on day 14. For another average cycle length the calculator adds (cycle length − 28) days to the due date and to every other date it shows, which amounts to assuming ovulation 14 days before the next period would have started. “Weeks pregnant today” is counted so that 40 weeks 0 days falls on the due date.
Frequently asked questions
- What is my due date if my last period was January 1, 2026?
- October 8, 2026, by the 280-day rule with a 28-day cycle. Some other starting dates: March 15, 2026 gives December 20, 2026; June 10, 2026 gives March 17, 2027; September 1, 2026 gives June 8, 2027.
- Is adding 280 days the same as Naegele’s rule of plus 7 days, minus 3 months?
- Not always to the day. The shortcut depends on the lengths of the months in between. For a last period that began on May 15, 2026 the shortcut gives February 22, 2027, and counting 280 days gives February 19, 2027. This calculator always counts 280 days.
- How accurate is a due date from the last period?
- It is an estimate. ACOG notes that only about half of women recall the date of their last period accurately and that the rule assumes ovulation on day 14. In an Australian study of 18,708 births after spontaneous labor, 5% happened on the estimated date and about 66% within 7 days of it.
- Will an ultrasound change my due date?
- It can. ACOG calls an ultrasound in the first trimester, up to 13 weeks 6 days, the most accurate way to establish gestational age, accurate to within about 5 to 7 days. Its guidance is to change the date when an ultrasound before 9 weeks differs from the last-period date by more than 5 days, or by more than 7 days from 9 weeks to 13 weeks 6 days. If your doctor or midwife gives you a different date from this calculator, use theirs.
- How does cycle length change the due date?
- Each day over 28 moves the due date one day later and each day under 28 moves it one day earlier. A 35-day cycle gives the last period plus 287 days, and a 24-day cycle gives plus 276. ACOG points out that the plain 280-day rule does not account for cycle length, and the shifted date is still an estimate.
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