Pregnancy Due Date Calculator
Use the method that best matches your situation for the most accurate estimate.
Educational tool only. Always confirm dating and pregnancy milestones with your OB-GYN or midwife.
How this accurate due date calculator works
This tool estimates your pregnancy due date using established obstetric formulas and the method you choose. Most pregnancies are dated to 40 weeks (280 days) from the first day of the last menstrual period, not from the day of conception. If you know conception or IVF transfer timing, those methods can be more precise than LMP alone.
A due date is an estimate, not a deadline. Many healthy births occur between 37 and 42 weeks. Still, an accurate estimate helps with prenatal scheduling, anatomy scans, leave planning, and preparing for delivery.
Which input method is most accurate?
1) Last Menstrual Period (LMP)
This is the standard method used at the start of prenatal care. The calculator applies Naegele-style dating and adjusts for cycle length. If your cycle is usually longer or shorter than 28 days, that can shift the estimate by several days.
2) Conception Date
If conception date is confidently known, due date is calculated as conception + 266 days (38 weeks). This can be very helpful for people tracking ovulation or using fertility treatment.
3) IVF Transfer Date
IVF dating is often the most precise because embryo age at transfer is known. The calculator uses transfer date and embryo age (day 3/day 5/day 6) to generate a clinical estimate.
What your result includes
- Estimated due date
- Current gestational age in weeks and days
- Trimester status
- Days remaining (or days overdue)
- Milestone dates, including full-term threshold
Why due dates can change later
Early ultrasound may revise your due date if fetal measurements differ meaningfully from menstrual dating. In clinical practice, first-trimester ultrasound can improve dating accuracy, especially if LMP is uncertain or cycles are irregular.
- Irregular cycles can make LMP less reliable.
- Late ovulation can make pregnancy seem “younger” than expected.
- Early ultrasound can provide a better biologic estimate.
Planning with a due date calculator
Medical appointments
Knowing gestational age helps you schedule routine prenatal visits, screening windows, and the anatomy scan timeline. Bring your calculator estimate to appointments, then follow your provider’s official dating after ultrasound review.
Practical planning
- Estimate parental leave and handoff timelines at work.
- Plan childcare transitions for older children.
- Spread out budget decisions for maternity, delivery, and postpartum essentials.
- Set reminder milestones for hospital bag prep and birth plan discussions.
Quick FAQ
Is a due date exact?
No. It is a best estimate of timing, and spontaneous labor can safely happen before or after that date.
Can this replace medical care?
No. This calculator is informational and should not replace diagnosis, ultrasound, or clinical advice.
What if I do not remember my exact LMP date?
Use the method you know best (conception or IVF) and confirm with your prenatal provider.
Final note
A reliable gestational age calculator is a practical starting point, especially early in pregnancy. For the most accurate timeline, pair this estimate with professional prenatal care and ultrasound-based confirmation.