Due Date Calculator
A due date calculator uses your last menstrual period (LMP) to predict when your baby will be born. The standard method (Naegele's Rule) adds 280 days (40 weeks) to the LMP. Due dates are estimates — only 4% of babies arrive on the exact predicted date.
Tip: Track your LMP accurately — the due date affects screening test timing, growth scan interpretation, and delivery decisions.
- 1Record the first day of your last menstrual period
- 2Add 280 days (or 9 months and 7 days) to get your due date
- 3Key milestones: conception ~day 14, heartbeat ~week 6, anatomy scan ~week 20
- 4Full term: 37–40 weeks; induced if past 41–42 weeks
IVF dating
For IVF pregnancies, the due date is calculated from the egg retrieval date: Day 3 transfer adds 263 days; Day 5 transfer adds 261 days.
Irregular cycles
Naegele's Rule assumes a 28-day cycle with ovulation on day 14. Women with longer cycles ovulate later, shifting the due date forward.
| Week | Milestone |
|---|---|
| 6 | Heartbeat detectable by ultrasound |
| 8–10 | First prenatal appointment |
| 12 | End of first trimester; risk of miscarriage drops significantly |
| 20 | Anatomy scan (fetal anomaly screening) |
| 24 | Viability threshold |
| 37 | Full term begins |
| 40 | Estimated due date |
Fun Fact
The record for the longest confirmed human pregnancy is 375 days (12.5 months), reported in a 1945 Los Angeles case.