Due Date Calculator
Enter the last menstrual period (LMP) date and cycle length to estimate the pregnancy due date (EDD) and current weeks of gestation.
Input Data
Results
At a glance:The due date (expected date of delivery, EDD) is estimated from the last menstrual period by Naegele's rule: 280 days (40 weeks) after LMP, with a correction of (cycle − 28) days for cycles other than 28 days. Gestational age counts from LMP (about two weeks before conception). The result is an estimate; ultrasound dating is more accurate, especially in the first trimester.
Formula
Due date = LMP + 280 days + (cycle − 28) days.
Gestational age (weeks) = (today − LMP) ÷ 7.
$$EDD = LMP + 280 + (c - 28)$$$$GA = \frac{t - LMP}{7}$$How to Use
- Enter the first day of the last menstrual period.
- Enter your average cycle length (default 28 days).
- The tool shows the due date and current weeks of gestation.
Case Studies
Standard 28-day cycle
LMP 2026-01-01, cycle 28 days.
Due date = 2026-01-01 + 280 days = 2026-10-08.
If today is 2026-03-12, gestational age ≈ 10.4 weeks.
FAQ
Is the due date exact?
No. It is a statistical estimate; only about 4–5% of babies arrive on the exact due date. A normal range is ±2 weeks.
Why adjust for cycle length?
Naegele's rule assumes a 28-day cycle. Longer cycles usually mean later ovulation, so the due date shifts later by (cycle − 28) days.
What is more accurate than LMP?
An early ultrasound (first-trimester crown-rump length) is the most accurate way to date a pregnancy.
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References
Content review: Calculatorism Health Team. Results are for reference only; please refer to the relevant authorities for the official figures.