Due Date Calculator
Forecast expected date of delivery using Naegele's rule adjusted for your cycle length.
Parameters & Inputs
Summary & Breakdown
Delivery Window Expectations
About the Due Date Calculator
Calculating your Estimated Date of Delivery (EDD) is one of the earliest milestones of pregnancy, establishing your calendar for prenatal checkups, screening tests, and maternity planning.
While German obstetrician Franz Naegele established the standard rule in the 19th century based on a 280-day cycle, modern clinical calculators must adjust for varying cycle lengths, known conception days, or assisted reproductive technology (IVF transfers).
This calculator supports all three methods and provides a real-time countdown to your baby's arrival.
How the Calculations Work
Computes delivery date using Naegele's rule: add 1 year, subtract 3 months, add 7 days to LMP, plus cycle correction (cycle length - 28 days). For conception, adds 266 days.
EDD = LMP + 280 days + (Cycle Days - 28) | IVF Day 5: Transfer Date + 261 days
Variables & Definitions
- Naegele rule: LMP + 1 year - 3 months + 7 days
- Cycle delta: Compensates for cycles longer or shorter than 28 days
- IVF Day 5: Transfer date + 266 - 5 = 261 days
For an LMP on May 10, 2026 with a 28-day cycle: Add 1 year (May 10, 2027), subtract 3 months (Feb 10, 2027), add 7 days -> Due date is February 17, 2027.
Key Terms Explained
Estimated Date of Delivery (EDD)
The projected delivery date corresponding to exactly 40 weeks 0 days gestational age.
Naegele's Rule
The historical standard formula: LMP plus one year, minus three months, plus seven days.
Early Term
Infants delivered between 37 weeks 0 days and 38 weeks 6 days of gestation.
IVF Embryo Transfer Dating
Dating based on the exact laboratory embryo transfer date (Day 3 or Day 5 blastocyst), offering absolute precision.
Practical Tips & Pitfalls to Avoid
View the due date as a window
Only 4-5% of births occur on the exact date; 80% arrive within two weeks before or after.
First trimester ultrasound is definitive
If your dating scan differs by more than a week, your doctor will adjust your official clinical EDD.
Schedule maternity leave flexibly
First-time mothers frequently deliver between 40 weeks 3 days and 41 weeks.
Pack your hospital bag by week 36
Having essentials ready a month in advance minimizes stress if baby arrives early term.
Frequently Asked Questions
Naegele's rule is accurate within a few days for regular 28-day cycles, but first-trimester crown-rump length ultrasound remains the gold standard.
A day-5 blastocyst is already 5 days old at transfer; therefore, remaining gestation is 266 - 5 = 261 days.
Most obstetricians monitor fetal heart rate and amniotic fluid volume closely past 40 weeks, and recommend induction between 41 and 42 weeks.
Late-pregnancy ultrasounds are not used to change due dates because fetal growth variations increase in the second and third trimesters.
At 40 weeks (280 days), pregnancy is 9 calendar months plus 1 week, or roughly 10 lunar (28-day) months.