Due Date Calculator
Calculate EDD, current gestational age, and trimester based on last menstrual period.
Important Medical Disclaimer
This calculator is an educational and clinical decision support tool. Results DO NOT replace professional medical evaluation, laboratory tests, or clinical judgment. Always consult a qualified healthcare professional for diagnosis, treatment, and clinical decisions. Calculations are based on scientifically validated formulas but may not be applicable to all patients.
Calculate Due Date
What is Due Date?
Estimated Due Date (EDD) is the estimate of when baby will be born, calculated by adding 280 days (40 weeks) to last menstrual period (LMP). Naegele's rule: LMP + 7 days - 3 months + 1 year. Only 5% of babies are born exactly on EDD. Full term: 37-42 weeks.
When to use Due Date?
Use to estimate delivery date in pregnancies with regular 28-day cycle and reliable LMP. If 1st trimester ultrasound differs >5-7 days from LMP-based EDD, adjust by ultrasound (more accurate). Useful for tracking gestational age, planning prenatal exams, and defining term. Don't use if LMP uncertain or irregular cycles.
Limitations and Considerations
LMP-based EDD assumes ovulation on 14th day of 28-day cycle. Irregular, short, or long cycles alter calculation. 1st trimester ultrasound (up to 13w6d) is gold standard for pregnancy dating (±5-7 days error). After 14 weeks, ultrasound less accurate. EDD doesn't predict exact delivery date, just probable window (37-42 weeks).
Frequently Asked Questions about Due Date
What if LMP-based EDD differs from ultrasound?
If 1st trimester ultrasound (up to 13w6d) differs >5-7 days from LMP-based EDD, use ultrasound EDD (more accurate). Example: LMP indicates 10 weeks, but ultrasound shows 12 weeks → consider 12 weeks. 2nd/3rd trimester ultrasound should not change already established EDD (less precision, reflects variable fetal growth).
How to calculate if cycle isn't 28 days?
Adjust EDD: if cycle is 35 days (+7 days from 28), add 7 days to EDD. If cycle is 21 days (-7 days), subtract 7 days. Formula: EDD = LMP + 280 days + (cycle days - 28). However, 1st trimester ultrasound is more reliable in these cases.
When to induce if past EDD?
Guidelines recommend offering induction between 41-42 weeks (post-dates). Stillbirth risk increases after 42 weeks. Between 39-41 weeks, individualized decision (maternal age, comorbidities, preference). Before 39 weeks, elective induction not recommended (except medical indication).
Does EDD work for twins?
EDD calculated same way, but twins usually born earlier. Average: 37 weeks (twins), 33 weeks (triplets). Don't expect 40 weeks. Obstetricians plan twin delivery for 37-38 weeks. More frequent monitoring in 3rd trimester.