How the Due Date Calculator works
The Due Date Calculator estimates the day your pregnancy reaches 40 weeks. Choose the method that matches what you know, enter the date, and the calculator returns your estimated due date (EDD) with the day of the week, how far along you are today, your trimester, the days remaining and a table of key dates. Four methods are available:
| Method | Calculation | Best when |
|---|---|---|
| Last period (LMP) | LMP + 280 days, adjusted for cycle length | You know the first day of your last period and cycles are fairly regular |
| Conception | Conception date + 266 days | You tracked ovulation or know the conception date |
| IVF transfer | Transfer date + 266 days − embryo age | You conceived through IVF or a frozen embryo transfer |
| Ultrasound | Scan date + (280 days − gestational age on the scan) | A scan has already measured how far along you are |
Due date by last menstrual period
This is the method most people start with, and the one used at most first appointments. The calculator adds 280 days to the first day of your last period (Naegele’s rule). If your cycle is not 28 days, open “Cycle length” and the date shifts by the difference, because ovulation usually happens about 14 days before the next period rather than on a fixed day 14.
Example: a last period that began on January 10, 2026 gives an estimated due date of October 17, 2026. With a 31-day cycle, the estimate becomes October 20, 2026.
Due date by conception date
Conception normally happens about 14 days after the start of the last period, so the due date is 280 − 14 = 266 days after conception. Enter the date you ovulated or conceived — for example from ovulation tests, temperature charting or a single possible date. Remember that sperm can survive for several days, so intercourse and conception are not always on the same day. The dedicated Due Date Calculator by Conception explains this in more detail.
IVF due date
With IVF the age of the embryo at transfer is known exactly, which makes IVF due dates the most precise. The calculator subtracts the embryo’s age from 266 days: a day-5 blastocyst transfer adds 261 days, a day-3 transfer adds 263 days, and a day-6 transfer adds 260 days. Using the egg retrieval date instead, it adds 266 days. See the IVF Due Date Calculator for fresh and frozen transfers.
Due date from an ultrasound
An ultrasound measures the embryo or fetus and reports a gestational age such as “9 weeks 2 days”. Enter the scan date and that measurement, and the calculator works out the due date: it subtracts the measured days (here 65) from 280 and adds the remaining 215 days to the scan date. First-trimester measurements, especially the crown–rump length between about 8 and 13 weeks, are considered the most reliable for dating.
Due date chart
For a quick look-up, find the month your last period started. The table shows the estimated due date for a period that began on the 1st or the 15th of each month this year, assuming a 28-day cycle. For any other day, move the due date forward by the same number of days — or simply use the calculator above.
| Last period started in | If it started on the 1st | If it started on the 15th |
|---|---|---|
| January 2026 | October 8, 2026 | October 22, 2026 |
| February 2026 | November 8, 2026 | November 22, 2026 |
| March 2026 | December 6, 2026 | December 20, 2026 |
| April 2026 | January 6, 2027 | January 20, 2027 |
| May 2026 | February 5, 2027 | February 19, 2027 |
| June 2026 | March 8, 2027 | March 22, 2027 |
| July 2026 | April 7, 2027 | April 21, 2027 |
| August 2026 | May 8, 2027 | May 22, 2027 |
| September 2026 | June 8, 2027 | June 22, 2027 |
| October 2026 | July 8, 2027 | July 22, 2027 |
| November 2026 | August 8, 2027 | August 22, 2027 |
| December 2026 | September 7, 2027 | September 21, 2027 |
Can my due date change?
Yes. It is common for a provider to adjust the due date after the first dating ultrasound if the scan measurement differs from the LMP estimate by more than a set margin — commonly around 5 to 7 days in the first trimester, with larger margins later. Once a due date has been confirmed by an early scan, it is usually not changed again by later scans, because growth varies more between babies as pregnancy progresses. IVF due dates are generally not changed.
A due date is an estimate of the middle of a window. Births from 37 weeks to the end of 41 weeks are common, and first babies are slightly more likely to arrive after the due date. The Days Until Due Date Calculator counts down to your date, and the Pregnancy Timeline lays out every week in between.
Key dates the calculator shows
- Estimated conception — about 266 days before the due date.
- End of the first trimester — 13 weeks 6 days.
- The common anatomy-scan window — around 18 to 22 weeks.
- Third trimester — from 28 weeks.
- Early term, full term and late term — 37, 39 and 41 weeks.
Want the full picture — your week, month, trimester and progress as well as the date? The main Pregnancy Calculator shows everything in one result.