Pregnancy Due Date Calculator
Estimate your due date and current week of pregnancy. Choose your starting point — last menstrual period, conception date, or IVF transfer date.
Show milestone timeline
| Milestone | Date | Week |
|---|
How due date is estimated
The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP), assuming a 28-day cycle. The math works because conception typically happens about 14 days after the start of your last period, and pregnancy from conception to birth is around 266 days — adding back the 14 gives 280 from LMP.
- LMP: due date = LMP + 280 days (adjusted for cycle length)
- Conception: due date = conception date + 266 days
- IVF Day-3 transfer: due date = transfer date + 263 days
- IVF Day-5 transfer: due date = transfer date + 261 days
How accurate is the due date?
Only about 5% of babies arrive on the exact calculated date. About 80% arrive within two weeks before or after. Late-pregnancy ultrasound dating is less reliable; first-trimester ultrasounds (weeks 8–13) are the gold standard and may shift your due date by up to a week.
The trimesters
| Trimester | Weeks | What's happening |
|---|---|---|
| First | 1 – 13 | Major organ development; highest miscarriage risk; morning sickness peaks |
| Second | 14 – 27 | "Honeymoon" trimester for many; first movements; anatomy scan around 20 weeks |
| Third | 28 – 40+ | Rapid growth; final organ maturation; baby positioning for birth |
Standard prenatal milestones
- Week 12: end of first trimester; first ultrasound dating
- Week 16–20: anatomy scan, sex can be determined
- Week 24: viability threshold (with intensive NICU care)
- Week 28: third trimester begins; glucose screening for gestational diabetes
- Week 36: Group B strep test; weekly visits begin
- Week 37: early-term — baby is no longer considered preterm if born now
- Week 39–40: full-term, due date
- Week 41+: late-term; induction often discussed by week 42
This calculator is for informational purposes only and is not medical advice. Always confirm dating with your healthcare provider, who has access to ultrasound measurements.