Due Date Calculator
Choose how you want to date your pregnancy, enter a date, and get your estimated due date plus the dates when early term, full term, and post-term begin.
Your calculation is performed in your browser.This result is an estimate for informational and educational purposes. It isn’t a diagnosis and isn’t a substitute for advice from a doctor, registered dietitian, or other qualified professional. See our methodology and sources for the formula used and its limitations.
How it works
A full-length pregnancy is 40 weeks (280 days) counted from the first day of your last period. Depending on the method you choose, the calculator adds 280 days to your last period, 266 days to your conception date, or the days remaining in the 40 weeks to your embryo transfer or ultrasound date. Every method ends in the same 40-week timeline, so the milestones always line up.
Formula & methodology
The calculator uses Naegele’s rule for last-period dating and the standard 266-day conception-to-birth interval for conception and IVF dating. For longer or shorter cycles, the last-period due date shifts by the difference from 28 days. For an ultrasound, your measured gestational age on the scan date is subtracted from 280 days to find how many days remain.
Due date = LMP + 280 days + (cycle length − 28)Due date = Conception date + 266 daysDue date = Transfer date + 266 days − embryo age (days)Due date = Scan date + (280 days − gestational age at scan in days)What each term means
- LMP
- The first day of your last menstrual period.
- Cycle length
- Days from the first day of one period to the first day of the next. Defaults to 28.
- Embryo age
- The age of the embryo in days at transfer: 3 for a day-3 embryo, 5 for a day-5 blastocyst, 6 for a day-6 blastocyst.
- Gestational age at scan
- The weeks and days of pregnancy measured on the ultrasound report.
IVF due date by embryo age
| Embryo age at transfer | Due date = transfer date + |
|---|---|
| Day 3 | 263 days |
| Day 5 | 261 days |
| Day 6 | 260 days |
Term definitions
| Stage | Gestational age |
|---|---|
| Early term | 37 weeks 0 days – 38 weeks 6 days |
| Full term | 39 weeks 0 days – 40 weeks 6 days |
| Late term | 41 weeks 0 days – 41 weeks 6 days |
| Post-term | 42 weeks 0 days and later |
Worked example
If the first day of your last period was January 1, 2026 and your cycle is 28 days, your due date is Thursday, October 8, 2026. Early term begins on September 17, full term on October 1, and post-term on October 22. With a day-5 embryo transferred on January 15, 2026, the due date is October 3, 2026. With an ultrasound on February 12, 2026 that measured 8 weeks and 3 days, the due date is September 21, 2026.
Common uses
- —Getting a first estimate of your due date after a positive pregnancy test.
- —Working out a due date from an IVF embryo transfer date.
- —Checking your due date against the gestational age on an ultrasound report.
- —Planning leave from work, appointments, and when you will reach full term.
Important notes
- —A due date is an estimate. Only a small share of babies are born on the exact date, and most arrive within a few weeks either side of it.
- —If you have an early ultrasound that gives a different date from your last period, your doctor or midwife will usually go with the ultrasound date. Always follow the dating your care provider gives you.
- —For IVF pregnancies, the transfer date is known exactly, so IVF dating is generally more precise than dating from a last period.
- —Conception is estimated unless you enter it yourself, because the exact moment of conception is rarely known.