Pregnancy Due Date Calculator
Pregnancy Due Date Calculator
This calculator estimates your pregnancy due date and current gestational age. It is for informational purposes only and does not replace clinical assessment. Due dates are estimates — only about 5% of babies are born on their exact due date. Always confirm with your healthcare provider.
Conversion Formula
LMP method (Naegele's rule): Due Date = LMP + 280 days. Conception method: Due Date = conception date + 266 days. IVF 5-day transfer: Due Date = transfer date + 261 days. All methods estimate the same biological endpoint: 40 weeks of pregnancy.
Step-by-Step Examples
LMP: 2026-01-05, mode: LMP = Due Date: 2026-10-12; ~40 weeks from LMP
Jan 5 + 280 days = Oct 12, 2026. This is standard Naegele's rule. Gestational age and trimester are calculated based on how many weeks have passed since Jan 5.
Transfer Date: 2026-02-20, mode: IVF 5-day = Due Date: 2026-11-08
Feb 20 + 261 days = Nov 8, 2026. The 261-day offset accounts for the embryo being 5 days old at transfer and the 14-day offset between LMP and ovulation.
History
Naegele's rule was formulated by Franz Karl Naegele (1778-1851), a German obstetrician. It has remained the standard calculation for due dates for nearly 200 years despite its simplifying assumptions.
Common Use Cases
- Pregnancy planning
- Birth preparation timeline
- Maternity leave planning
- OB appointment scheduling
- IVF cycle planning
Frequently Asked Questions
What is Naegele's rule?
Naegele's rule calculates the estimated due date (EDD) by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). For example, if your LMP was January 1, 2026, the due date is October 8, 2026. This assumes a 28-day cycle with ovulation on day 14.
What is the difference between LMP and conception date?
The LMP date is 2 weeks before conception in a typical cycle, because ovulation occurs around day 14. Gestational age is counted from LMP, so a pregnancy is "4 weeks along" at the point of a missed period, even though the embryo is only about 2 weeks old (fertilization age). Due dates from LMP add 280 days; from conception, they add 266 days.
Why might my doctor change my due date?
Ultrasound measurements (especially in the first trimester) are more accurate than cycle-based calculations, particularly if your cycles are irregular. A first-trimester ultrasound can be accurate to within 5-7 days. Your OB may adjust the due date if ultrasound dating differs significantly from LMP dating.
How accurate is the estimated due date?
Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the EDD. The due date is a 40-week midpoint estimate, not a deadline. Full-term pregnancy is 37-42 weeks.
How is an IVF due date calculated?
For a 5-day blastocyst transfer, the due date is 261 days (37 weeks + 2 days) from the transfer date. This accounts for the fact that a 5-day embryo is already 5 days past fertilization, so the gestational clock started 14 days before the LMP equivalent, minus 5 days already elapsed = LMP + 280 - 14 - 5 = transfer + 261.