Free tool
Pregnancy due date calculator
Enter your last period, known conception date or IVF transfer date to get an estimated due date, your current gestational week and trimester. A general estimate only, not a diagnosis: nothing you enter is stored or sent anywhere.
Estimated due date
This is a general estimate using standard obstetric formulas (Naegele’s rule and conception-based dating), not medical advice and not a diagnosis. Your doctor’s assessment and ultrasound scan are authoritative: always confirm your dates and due date with your doctor.
Key takeaways
- Naegele’s rule adds 280 days. Your estimated due date (EDD) is 280 days, or 40 weeks, after the first day of your last period.
- Conception and IVF dating can be more precise. If you know your conception date or embryo transfer date, dating from that skips the guesswork around ovulation timing.
- Only a small share of babies arrive exactly on the EDD. Full term is generally considered 37 to 42 weeks: the EDD is the midpoint of a normal range, not a deadline.
- Your dating ultrasound overrides this calculator. If your first-trimester scan gave a different due date, follow the scan and your doctor, not this estimate.
The three trimesters
| Trimester | Weeks | General milestone |
|---|---|---|
| First trimester | Week 1 to 13 | Dating is set here, ideally confirmed by a first scan. |
| Second trimester | Week 14 to 27 | The anomaly / mid-pregnancy scan usually happens in this window. |
| Third trimester | Week 28 to birth | Full term is generally considered 37 to 42 weeks. |
FAQ
How accurate is a due date calculated from my last period?
Naegele’s rule (last period plus 280 days) is a standard estimate, not a guarantee. It assumes a textbook 28-day cycle with ovulation around day 14, so it can be off by several days to two weeks for people with irregular, longer or shorter cycles. A first-trimester dating ultrasound is generally considered more accurate than last-period dating alone.
What if I do not know my last period, or my cycles are irregular?
Use the conception date option if you know it, or the IVF transfer date option if that applies to you: both are usually more precise than last-period dating when cycles are irregular. Otherwise your doctor can estimate your due date from a first-trimester ultrasound, which measures the baby directly rather than relying on reported dates.
How is the due date calculated from an IVF embryo transfer date?
For a standard IVF cycle, the embryo’s age at transfer (commonly day 3 or day 5) is used to work back to an equivalent conception date, then 266 days are added. A day 5 (blastocyst) transfer typically adds 261 days from the transfer date, and a day 3 transfer typically adds 263 days. Confirm the exact protocol and dating with your fertility clinic.
What are the three trimesters of pregnancy?
The first trimester generally covers week 1 through week 13, the second trimester week 14 through week 27, and the third trimester week 28 through birth, usually around week 40. Full term is generally considered 37 to 42 weeks. Your doctor tracks the specific milestones for your pregnancy.
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