Due Date Calculator
Estimate your pregnancy due date from your last period (Naegele's rule with adjustable cycle length), conception date, or IVF transfer. See gestational age, trimester, conception date, and a 40-week milestone timeline.
Choose a method and enter a date to estimate the due date.
How the due date is calculated
Pregnancy is dated from the first day of the last menstrual period (LMP), not conception — that is the one date most people can identify. Naegele's rule adds 280 days (40 weeks) to the LMP.
EDD = LMP + 280 days + (cycle length − 28)
EDD = conception date + 266 days
EDD = embryo transfer + (266 − embryo age)
Naegele's rule assumes a 28-day cycle with ovulation on day 14. A longer or shorter cycle shifts ovulation, so this tool lets you set your real cycle length for a more accurate estimate. IVF removes the guesswork entirely because the embryo age and transfer date are known precisely.
The three trimesters
| Trimester | Weeks | Highlights |
|---|---|---|
| First | 0 – 13 | Organs form, heartbeat ~6 w, highest miscarriage risk |
| Second | 14 – 27 | Anatomy scan ~20 w, movement felt, viability ~24 w |
| Third | 28 – 40 | Rapid growth, full term at 37 w, birth ~40 w |
Key milestones
6 weeks
Heartbeat often detectable
12 weeks
End of first trimester
20 weeks
Anatomy ultrasound, halfway
24 weeks
Threshold of viability
28 weeks
Third trimester begins
37 weeks
Considered full term
How accurate is a due date?
Only about 4–5% of babies arrive on the exact estimated date. Most births happen within the two weeks around it — anywhere from 37 to 42 weeks is normal. A first-trimester dating ultrasound (crown–rump length) is the most accurate method and may revise the date by several days.
This calculator gives an estimate for planning only and is not medical advice. Always confirm dating with your healthcare provider.