How is due date calculated?

Using Naegele's Rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP). If cycle length differs from 28 days, the due date is adjusted accordingly. For conception date, add 266 days. For IVF, based on embryo transfer day.

How accurate is the due date?

Only about 5% of babies arrive on the exact due date, but approximately 80% are born within two weeks (before or after). First‑trimester ultrasound dating improves accuracy.

What if my cycles are irregular?

Irregular cycles make LMP‑based estimates less accurate. Use the conception date method if you tracked ovulation, or adjust the average cycle length field. An early ultrasound provides the most reliable dating.

Can I use metric units?

This calculator uses standard calendar dates (YYYY‑MM‑DD), which are universal. Cycle length is in days.

Professional Due Date Calculator — Pregnancy Timeline & Milestones

Understanding Your Due Date

Your estimated due date (EDD) marks the expected arrival of your baby, calculated as 40 weeks from the first day of your last menstrual period (LMP). This Professional Due Date Calculator uses Naegele's rule—the standard obstetric method—adjusting for your individual cycle length. It also supports conception date and IVF transfer methods, and provides a detailed timeline of trimesters and key pregnancy milestones.

Calculation Methods

Last Menstrual Period (LMP): Adds 280 days (40 weeks) to LMP, adjusted by cycle length (cycles longer than 28 days add extra days; shorter subtract).
Conception Date: Adds 266 days (38 weeks) from the estimated date of conception.
IVF Transfer: For Day 3 embryos, adds 263 days; for Day 5 embryos, adds 261 days from transfer date.

💡 When Is a Pregnancy Considered Full Term?

Early term: 37‑38 weeks. Full term: 39‑40 weeks. Late term: 41 weeks. Post‑term: 42+ weeks. Delivery between 39 and 40 weeks is associated with the best outcomes.

Your Pregnancy Timeline

The calculator shows your current gestational age (weeks + days) and progress through the three trimesters. It also highlights key milestones: viability (24 weeks), full term (39 weeks), and the end of each trimester.

Frequently Asked Questions

Can my due date change?

Yes. Your healthcare provider may adjust it based on ultrasound measurements, especially in the first trimester.

What if I have irregular periods?

Use the conception date method if you know it, or enter your best estimate of average cycle length. An early ultrasound is recommended for accurate dating.

How is IVF due date different?

IVF dating is more precise because the date of fertilization/transfer is known. The calculator adjusts based on whether a Day 3 or Day 5 embryo was transferred.

What percentage of babies arrive on their due date?

Only about 5%. Most babies (80%) are born within two weeks (before or after) the estimated date.

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