Pregnancy Due Date & Gestational Age Calculator
A pregnancy due date is calculated from the first day of the last menstrual period (LMP) using Naegele's Rule, which assumes a 280-day (40-week) gestation period.
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📐 Formula
💡 Practical Example
LMP Date Jan 1, 2026 with standard 28-day cycle: Estimated Due Date (EDD) = October 8, 2026 (40 full weeks). Estimated Conception Date = January 15, 2026.
📖 About Pregnancy Due Date & Gestational Age Calculator
A pregnancy due date is calculated from the first day of the last menstrual period (LMP) using Naegele's Rule, which assumes a 280-day (40-week) gestation period.
To use the Pregnancy Due Date & Gestational Age Calculator, enter your Calculation Method, Input Date (YYYY-MM-DD), Average Menstrual Cycle Length. The calculator instantly computes Estimated Due Date (EDD), Current Gestational Age and more. Results update in real time as you change any input — no submit button needed.
How to Use This Calculator
Enter your Calculation Method — select from First Day of Last Menstrual Period (LMP), Known Conception Date, Input Date (YYYY-MM-DD) (e.g. 2026-01-01), and Average Menstrual Cycle Length (e.g. 28 in days). Results update instantly — no submit button needed. Use metric or imperial units as labeled. For the most accurate result, measure height and weight in the morning without shoes.
The Formula
Naegele's Rule (EDD): LMP Date + 280 Days (40 Weeks) + (Cycle Length - 28 Days)
From Conception Date: Conception Date + 266 Days (38 Weeks)
Gestational Age = Current Date - LMP Date in Weeks & Days
Worked Example
LMP Date Jan 1, 2026 with standard 28-day cycle:
Estimated Due Date (EDD) = October 8, 2026 (40 full weeks).
Estimated Conception Date = January 15,
2026.
Understanding Your Result
Naegele's Rule (LMP + 280 days) gives the estimated due date — only about 5% of babies arrive on their exact due date. The normal delivery window is 37–42 weeks gestation. Babies born 37–38+6 weeks are "early term" and may have higher risk of respiratory and feeding difficulties than babies born 39–40 weeks. Ovulation typically occurs 12–16 days before the next menstrual period, not necessarily on day 14 — cycle length variation shifts this window significantly.
💡 Expert Health Guidance & Clinical Context
- This calculator uses clinically validated formulas and population reference data published by the WHO and NIH. Results are screening estimates, not medical diagnoses.
- Consult a licensed healthcare provider before making any changes to diet, medication, or exercise based on these results — individual variation is significant.
- Genetics, chronic conditions, and concurrent medications can dramatically affect what a "normal" result means for a specific individual.
- Track your results over time: a single data point is less meaningful than a trend measured consistently across multiple weeks or months.
- The CDC recommends adults receive routine health screenings at least annually. Use these calculations to prepare informed questions for your physician.
- Body composition, lifestyle factors, and stress levels all interact with the metrics shown here. No single number captures your full health picture.
- For pediatric or geriatric populations, reference ranges may differ significantly from the adult standards used in general calculators.
- Always cross-reference results with laboratory tests, clinical examinations, and professional medical evaluation before acting on any finding.
Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.