Estimate Your Pregnancy Due Date
The average pregnancy lasts 40 weeks from the first day of your last menstrual period (LMP). This calculator gives you your due date, current trimester, and key milestone dates. Estimates only - always confirm with your OB/GYN or midwife.
How Due Dates Are Calculated
The standard method is Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period.
If you know your conception date (usually 2 weeks after LMP), add 266 days instead.
Pregnancy Timeline
| Week | Trimester | What Happens |
|---|---|---|
| Weeks 1-4 | First | Conception, implantation |
| Weeks 5-8 | First | Heartbeat detectable, organs forming |
| Weeks 9-12 | First | Fingers, toes, facial features |
| Weeks 13-27 | Second | Movement felt, anatomy scan |
| Weeks 28-40 | Third | Rapid growth, lung development |
| Week 40 | Due | Full-term delivery window |
Key Milestone Dates
- End of first trimester: LMP + 12 weeks
- Anatomy scan window: 18-22 weeks
- Viability milestone: 24 weeks
- Third trimester begins: 28 weeks
- Full term: 37-42 weeks
Accuracy of Due Dates
Only about 4% of babies are born on their exact due date. Most deliveries happen within 2 weeks before or after. First-trimester ultrasound is the most accurate method - often more accurate than LMP-based calculation.
Frequently Asked Questions
How accurate is the due date?
LMP-based estimates are accurate within 2 weeks for most women. First-trimester ultrasound is more precise, especially if your cycle is irregular.
What if I do not know my LMP?
Your doctor can use an early ultrasound to estimate gestational age more accurately.
Can my due date change?
Yes - if an early ultrasound measures a different gestational age, your doctor may adjust the due date.
What is a full-term pregnancy?
37-42 weeks. Early term: 37-38. Full term: 39-40. Late term: 41. Post term: 42+.
What is the difference between gestational age and fetal age?
Gestational age is counted from LMP (usually 2 weeks longer). Fetal age is counted from conception.
What are common pregnancy milestones?
First heartbeat: 6-8 weeks. First trimester ends: 12 weeks. Anatomy scan: 20 weeks. Viability: 24 weeks.