Due Date Calculator
Calculate your estimated due date (EDD) from your last menstrual period (LMP), conception date or ultrasound dating.
How to use the Due Date Calculator
- Enter your inputs into the Due Date Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The EDD formulas
Naegele's rule (LMP): EDD = LMP + 280 days · · · From conception: EDD = Conception + 266 days · · · Adjust for cycle length variation
The 280-day standard assumes a 28-day cycle ovulating on day 14. For cycle lengths X, add (X − 28) days to the LMP-based due date.
Worked example
LMP February 10 with regular 28-day cycle: EDD = November 16 (280 days later). LMP February 10 with 32-day cycle: EDD = November 20 (add 4 days for the longer cycle).
Frequently asked questions
Why is my ultrasound EDD different from my LMP EDD?
Early ultrasound (8–14 weeks) is more accurate than LMP-based dating, especially if cycle length is irregular or LMP date is uncertain. Most obstetricians adjust EDD to match ultrasound when they differ by more than 5–7 days.
What is "term" vs. "preterm" vs. "post-term"?
Term: 37–41 weeks 6 days. Preterm: before 37 weeks. Post-term: after 42 weeks. Most deliveries happen between 37 and 41 weeks.
How often is the EDD actually correct?
Only ~4% of babies are born on the exact EDD. About 70% deliver within ±10 days of EDD. About 80% deliver between 38 and 42 weeks.